An original Thinka practice paper modelled on the structure and difficulty of the June 2025 — Foundation OCR GCSE (9-1) Twenty First Century Science - Chemistry B - J258 paper. Not affiliated with or reproduced from OCR.
Paper 1: Breadth in Chemistry (Foundation)
Answer all ten questions in the spaces provided. 90 marks, 1 hour 45 minutes. Calculators, ruler and data sheet allowed.
51 Question · 86.4 marks
Question 1 · Tick-box / true-false
1.6 marks
Potassium is an element in Group 1 of the Periodic Table.
Which statement about Group 1 elements is correct? Tick (✓) one box.
☐ They are hard and have very high melting points. ☐ They react with water to produce hydrogen gas. ☐ They form negative ions with a charge of 1−. ☐ They are less reactive as you go down the group.
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Worked solution
Group 1 metals are soft with low melting points, form 1+ ions and become more reactive down the group. They react with water to give a metal hydroxide and hydrogen gas.
Marking scheme
Second box ticked = 1.6 marks (AO1.1). Any other box, or more than one box ticked = 0 marks.
Question 2 · Tick-box / true-false
1.6 marks
Sodium chloride is an ionic compound.
Tick (✓) one box in each row to show whether each statement about sodium chloride is true or false.
| Statement | True | False | |---|---|---| | Solid sodium chloride conducts electricity. | ☐ | ☐ | | Molten sodium chloride conducts electricity. | ☐ | ☐ | | Sodium chloride has a high melting point. | ☐ | ☐ | | Sodium chloride is made of small separate molecules. | ☐ | ☐ |
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Worked solution
In the solid the ions are fixed in a lattice so cannot carry charge. When molten the ions are free to move, so it conducts. Strong attractions between oppositely charged ions in the giant lattice give a high melting point. It is a giant lattice, not small molecules.
Marking scheme
All four rows correct = 1.6 marks; three correct = 1.2 marks; two correct = 0.8 marks; one correct = 0.4 marks; none = 0 (AO1.1). A row with both boxes ticked scores zero for that row.
Question 3 · Tick-box / true-false
1.6 marks
Crude oil is separated into fractions by fractional distillation.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | Crude oil is a mixture of hydrocarbons. | ☐ | ☐ | | Fractions with smaller molecules have higher boiling points. | ☐ | ☐ | | Crude oil is a finite resource. | ☐ | ☐ | | Alkanes have the general formula \(C_nH_{2n+2}\). | ☐ | ☐ |
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Worked solution
Crude oil is a mixture of hydrocarbons and will run out because it forms very slowly. Smaller molecules have weaker intermolecular forces so lower boiling points. Alkanes follow \(C_nH_{2n+2}\).
Marking scheme
All four rows correct = 1.6 marks; three correct = 1.2 marks; two correct = 0.8 marks; one correct = 0.4 marks; none = 0 (AO1.1). A row with both boxes ticked scores zero for that row.
Question 4 · Tick-box / true-false
1.6 marks
A student reacts magnesium ribbon with dilute hydrochloric acid and measures how fast hydrogen gas is made.
Which change would NOT make the reaction faster? Tick (✓) one box.
☐ Using magnesium powder instead of ribbon. ☐ Warming the acid before adding the magnesium. ☐ Using a more concentrated acid. ☐ Using the same acid but diluted with extra water.
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Worked solution
Powder has a larger surface area, warmer particles collide more often and with more energy, and higher concentration means more frequent collisions. Dilution lowers the concentration, so fewer collisions per second and a slower reaction.
Marking scheme
Fourth box ticked = 1.6 marks (AO2.1). Any other box, or more than one box ticked = 0 marks.
Question 5 · Tick-box / true-false
1.6 marks
Carbon dioxide is a greenhouse gas.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | Burning fossil fuels releases carbon dioxide into the atmosphere. | ☐ | ☐ | | Greenhouse gases absorb and re-emit infrared radiation from the Earth. | ☐ | ☐ | | Planting new forests increases the amount of carbon dioxide in the atmosphere. | ☐ | ☐ | | A graph showing carbon dioxide level and temperature rising together proves that one causes the other. | ☐ | ☐ |
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Worked solution
Combustion of fossil fuels releases carbon dioxide. Greenhouse gases absorb and re-emit infrared radiation. Growing trees remove carbon dioxide by photosynthesis. A correlation does not on its own prove causation.
Marking scheme
All four rows correct = 1.6 marks; three correct = 1.2 marks; two correct = 0.8 marks; one correct = 0.4 marks; none = 0 (AO1.1/AO3). A row with both boxes ticked scores zero for that row.
Question 6 · Tick-box / true-false
1.6 marks
A student adds dilute acid to a metal carbonate in a beaker and the temperature of the mixture falls.
Which statement about this reaction is correct? Tick (✓) one box.
☐ The reaction is exothermic and releases energy to the surroundings. ☐ The reaction is endothermic and takes in energy from the surroundings. ☐ The reaction has no energy change. ☐ More energy is released when bonds break than when bonds form.
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Worked solution
A fall in temperature means energy is transferred from the surroundings to the reaction mixture, so the reaction is endothermic.
Marking scheme
Second box ticked = 1.6 marks (AO2.1). Any other box, or more than one box ticked = 0 marks.
Question 7 · Tick-box / true-false
1.6 marks
Molten lead bromide is electrolysed using inert electrodes.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | Lead forms at the negative electrode. | ☐ | ☐ | | Bromine forms at the negative electrode. | ☐ | ☐ | | The ions must be free to move for the compound to be electrolysed. | ☐ | ☐ | | Positive ions move towards the positive electrode. | ☐ | ☐ |
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Worked solution
Positive lead ions move to the negative electrode and gain electrons to form lead. Bromide ions move to the positive electrode and form bromine. Ions can only move to the electrodes when molten or dissolved.
Marking scheme
All four rows correct = 1.6 marks; three correct = 1.2 marks; two correct = 0.8 marks; one correct = 0.4 marks; none = 0 (AO1.1). A row with both boxes ticked scores zero for that row.
Question 8 · Tick-box / true-false
1.6 marks
Nanoparticles are used in some sun creams.
Which statement about nanoparticles is correct? Tick (✓) one box.
☐ Nanoparticles are between 1 nm and 100 nm in size. ☐ Nanoparticles have a smaller surface area compared with their volume than larger particles of the same material. ☐ The risks of nanoparticles are fully understood, so no more testing is needed. ☐ Nanoparticles are always made of carbon.
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Worked solution
Nanoparticles are 1–100 nm across. They have a larger surface area to volume ratio than bigger particles, their risks are still being studied, and they can be made from many materials.
Marking scheme
First box ticked = 1.6 marks (AO1.1). Any other box, or more than one box ticked = 0 marks.
Question 9 · Tick-box / true-false
1.6 marks
A student revises the elements in Group 1 and Group 7 of the Periodic Table.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | Potassium is more reactive than lithium. | ☐ | ☐ | | Chlorine will displace iodine from potassium iodide solution. | ☐ | ☐ | | Group 7 elements become more reactive going down the group. | ☐ | ☐ | | Sodium reacts with water to produce hydrogen gas. | ☐ | ☐ |
[1.6]
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Worked solution
Group 1 reactivity increases down the group, so potassium is more reactive than lithium (true). Chlorine is more reactive than iodine so it displaces it (true). Group 7 reactivity decreases down the group (false). Sodium reacts with water to form sodium hydroxide and hydrogen (true).
Marking scheme
All four rows correct = 1.6 marks (4 x 0.4). Award 0.4 marks for each correct row. Only one box ticked per row; two ticks in a row scores zero for that row. Total 1.6.
Question 10 · Tick-box / true-false
1.6 marks
Substances have different structures and properties.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | Solid sodium chloride conducts electricity because its ions are free to move. | ☐ | ☐ | | Diamond has a very high melting point because of its many strong covalent bonds. | ☐ | ☐ | | Simple molecular substances have low boiling points because covalent bonds break easily when they boil. | ☐ | ☐ | | Graphite conducts electricity because it has delocalised electrons. | ☐ | ☐ |
[1.6]
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Worked solution
In solid sodium chloride the ions are fixed in a lattice, so it does not conduct (false). Diamond is a giant covalent structure with strong bonds throughout (true). When simple molecules boil, the weak intermolecular forces are overcome, not the covalent bonds (false). Graphite has delocalised electrons between layers that carry charge (true).
Marking scheme
0.4 marks for each correct row, total 1.6. Two ticks in one row scores zero for that row. Contradictions score zero.
Question 11 · Tick-box / true-false
1.6 marks
A student investigates how quickly magnesium ribbon reacts with dilute hydrochloric acid.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | Using powdered magnesium instead of ribbon increases the rate of reaction. | ☐ | ☐ | | Increasing the temperature makes the particles collide less often. | ☐ | ☐ | | A catalyst is used up in the reaction. | ☐ | ☐ | | Using a more concentrated acid increases the number of collisions per second. | ☐ | ☐ |
[1.6]
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Worked solution
Powder has a larger surface area so more collisions per second (true). Higher temperature makes particles move faster and collide more often (false). A catalyst is not used up (false). Higher concentration means more particles in the same volume, so more frequent collisions (true).
Marking scheme
0.4 marks for each correct row, total 1.6. Two ticks in one row scores zero for that row.
Question 12 · Tick-box / true-false
1.6 marks
Scientists study the causes and effects of climate change.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | Carbon dioxide and methane are greenhouse gases. | ☐ | ☐ | | Burning fossil fuels adds carbon dioxide to the atmosphere. | ☐ | ☐ | | Planting new forests increases the amount of carbon dioxide in the atmosphere. | ☐ | ☐ | | A correlation between two variables always proves that one causes the other. | ☐ | ☐ |
[1.6]
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Worked solution
Both gases absorb infrared radiation (true). Combustion of carbon-containing fuels forms carbon dioxide (true). Growing trees remove carbon dioxide by photosynthesis (false). Correlation does not prove causation without a plausible mechanism (false).
Marking scheme
0.4 marks for each correct row, total 1.6. Two ticks in one row scores zero for that row.
Question 13 · Tick-box / true-false
1.6 marks
A technician passes an electric current through molten lead bromide using inert electrodes.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | The lead bromide must be molten so that its ions can move. | ☐ | ☐ | | Lead forms at the positive electrode. | ☐ | ☐ | | Bromine forms at the positive electrode. | ☐ | ☐ | | Metal ions gain electrons during electrolysis. | ☐ | ☐ |
[1.6]
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Worked solution
Ions are free to move only when molten (true). Positive lead ions move to the negative electrode, so lead forms there (false). Negative bromide ions move to the positive electrode and form bromine (true). Metal ions are reduced by gaining electrons at the negative electrode (true).
Marking scheme
0.4 marks for each correct row, total 1.6. Two ticks in one row scores zero for that row.
Question 14 · Tick-box / true-false
1.6 marks
Our model of the atom has changed over time.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | A neutron has a relative charge of +1. | ☐ | ☐ | | Rutherford's experiments showed that most of an atom's mass is in a small nucleus. | ☐ | ☐ | | An atom has equal numbers of protons and electrons. | ☐ | ☐ | | Bohr suggested that electrons orbit the nucleus in shells. | ☐ | ☐ |
[1.6]
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Worked solution
A neutron has no charge (false). Rutherford's scattering results showed a small, dense nucleus (true). Atoms are neutral so protons equal electrons (true). Bohr proposed electrons in shells at fixed distances (true).
Marking scheme
0.4 marks for each correct row, total 1.6. Two ticks in one row scores zero for that row.
Question 15 · Complete / fill-in / match / draw or plot
2 marks
Lithium, sodium and potassium are in Group 1 of the Periodic Table.
Complete the sentences. Use words from the list. Each word can be used once, more than once or not at all.
list: one seven lose gain more less hydrogen oxygen
(a) Atoms of Group 1 elements have ........... electron in their outer shell. [1]
(b) Potassium is ........... reactive than sodium. [1]
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Worked solution
Group 1 atoms have one outer electron. Reactivity increases down the group, and potassium is below sodium, so it is more reactive.
Marking scheme
(a) one [1] (b) more [1] DO NOT ALLOW any other word. Contradictions (two words in one gap) score zero for that gap.
Question 16 · Complete / fill-in / match / draw or plot
2 marks
Magnesium reacts with oxygen to form magnesium oxide, an ionic compound.
Complete the sentences. Use words from the list. Each word can be used once, more than once or not at all.
Question 17 · Complete / fill-in / match / draw or plot
2 marks
Draw one straight line from each substance to its correct property. Draw only three lines.
Substance Property Diamond A Conducts electricity because it has delocalised electrons Graphite B Very hard because every carbon atom has four strong covalent bonds Sodium chloride (solid) C Does not conduct electricity because its ions cannot move
(Write the letter A, B or C next to each substance.)
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Worked solution
Diamond is a giant covalent structure with four bonds per carbon, so it is very hard. Graphite has delocalised electrons between layers so it conducts. Solid ionic compounds have ions held in a lattice and cannot conduct.
Marking scheme
All three correct [2] Two correct [1] One or none correct [0] More than one letter for a substance scores zero for that substance.
Question 18 · Complete / fill-in / match / draw or plot
2 marks
The table shows the relative charge of the three particles found in an atom.
Complete the table.
Particle | Relative charge | Where it is found in the atom Proton | +1 | ........... Neutron | ........... | in the nucleus Electron | ........... | in shells around the nucleus
[2]
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Worked solution
Protons are in the nucleus with charge +1, neutrons have no charge, and electrons have charge -1.
Marking scheme
All three entries correct [2] Two correct [1] ALLOW neutral / none / zero for neutron charge. ALLOW (-)1 for electron only if the minus sign is clearly shown; DO NOT ALLOW 1 or +1.
Question 19 · Complete / fill-in / match / draw or plot
2 marks
A student reacts magnesium with dilute hydrochloric acid and measures the volume of hydrogen gas collected every 20 seconds.
Table 5.1 Time (s): 0, 20, 40, 60, 80 Volume of gas (cm3): 0, 22, 36, 44, 46
The grid for Fig. 5.1 has time (s) on the x-axis (0 to 80) and volume of gas (cm3) on the y-axis (0 to 50). The points for 0, 20 and 40 s are already plotted.
(a) Plot the points for 60 s and 80 s on Fig. 5.1. [1]
(b) Draw a smooth curve of best fit through all the points. [1]
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Worked solution
Plot (60, 44) and (80, 46) to within half a small square, then draw a smooth curve that starts steeply and flattens as the acid or magnesium is used up.
Marking scheme
(a) both points plotted correctly (within half a small square) [1] (b) smooth curve through (or very close to) all points, with no straight-line segments and no curve beyond the data [1] DO NOT ALLOW a ruled dot-to-dot line for (b). ECF from (a) for (b).
Question 20 · Complete / fill-in / match / draw or plot
2 marks
Metals are extracted from their ores in different ways. Carbon is more reactive than iron but less reactive than aluminium.
Complete the table. Tick (✓) one box in each row to show the method used to extract each metal.
Metal | Heating with carbon | Electrolysis Iron | [ ] | [ ] Aluminium | [ ] | [ ]
[2]
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Worked solution
Metals less reactive than carbon (iron) can be displaced from their oxides by heating with carbon. Metals more reactive than carbon (aluminium) must be extracted by electrolysis.
Marking scheme
Iron: heating with carbon ticked only [1] Aluminium: electrolysis ticked only [1] Two ticks in a row scores zero for that row.
Question 21 · Complete / fill-in / match / draw or plot
2 marks
Some gases in the atmosphere cause the greenhouse effect.
Complete the sentences. Use words from the list. Each word can be used once, more than once or not at all.
Burning fossil fuels releases ........... into the atmosphere. Greenhouse gases ........... infrared radiation from the Earth's surface, which warms the atmosphere. [2]
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Worked solution
Combustion of fossil fuels releases carbon dioxide. Greenhouse gases absorb infrared radiation emitted by the Earth, keeping heat in the atmosphere.
Question 22 · Complete / fill-in / match / draw or plot
2 marks
A water company makes drinking water from river water. The steps are listed below in the wrong order.
A Chlorine is added to kill microorganisms. B River water is collected in a reservoir. C Water is passed through beds of sand and gravel to remove solid particles.
Write the letters A, B and C in the boxes to show the correct order. Step 1 has been done for you.
Step 1: B Step 2: [ ] Step 3: [ ]
[2]
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Worked solution
Water is collected, filtered to remove solids, then chlorinated to kill microorganisms.
Marking scheme
Step 2 = C [1] Step 3 = A [1] ALLOW ECF if C and A are swapped only for no more than 1 mark.
Question 23 · Complete / fill-in / match / draw or plot
2 marks
Magnesium reacts with oxygen to form magnesium oxide, an ionic compound.
Complete the sentences. Use words from the list. Each word can be used once, more than once or not at all.
covalent gain lattice lose share molecule
In the reaction, each magnesium atom will ........................ two electrons to form a positive ion. [1]
The ions in magnesium oxide are held together in a giant ........................ by strong forces of attraction between oppositely charged ions. [1]
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Worked solution
Metal atoms form positive ions by losing electrons. Ionic compounds consist of a giant lattice of oppositely charged ions.
Marking scheme
Mark 1: lose (1) Mark 2: lattice (1) Guidance: DO NOT ALLOW more than one word per gap. Contradictions score zero.
Question 24 · Complete / fill-in / match / draw or plot
2 marks
Scientists have changed the model of the atom as new evidence was found.
Draw lines to connect each scientist with the correct idea or discovery. Draw one line from each scientist.
Scientist Idea or discovery
Thomson • • Electrons move in fixed energy levels (shells) around the nucleus Rutherford • • Atoms contain tiny negatively charged particles, in a ball of positive charge Bohr • • Most of the mass of an atom is in a tiny, positively charged nucleus
[2]
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Worked solution
Thomson discovered the electron and proposed the plum-pudding model. Rutherford's scattering results showed a small dense positive nucleus. Bohr proposed electrons in fixed shells.
Marking scheme
All three lines correct = 2 marks (2) Two lines correct = 1 mark (1) One or none correct = 0 marks Guidance: DO NOT ALLOW more than one line from a scientist (that line scores zero).
Question 25 · Complete / fill-in / match / draw or plot
2 marks
A student reacts magnesium ribbon with dilute hydrochloric acid and changes one condition each time.
Complete the table. Tick (✓) one box in each row to show the effect of the change on the rate of reaction.
| Change | Rate increases | Rate decreases | Rate stays the same | |---|---|---|---| | Increasing the temperature of the acid | ☐ | ☐ | ☐ | | Using a more dilute acid | ☐ | ☐ | ☐ |
[2]
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Worked solution
Higher temperature means particles move faster, so collisions are more frequent and more energetic, increasing the rate. A more dilute acid has fewer particles per volume, so collisions are less frequent, decreasing the rate.
Marking scheme
Row 1: Rate increases ticked only (1) Row 2: Rate decreases ticked only (1) Guidance: More than one tick in a row scores zero for that row.
Question 26 · Calculation
2 marks
A technician has 20 g of sodium hydroxide, NaOH, to make a cleaning solution.
The relative formula mass (\(M_r\)) of sodium hydroxide is 40.
Calculate the number of moles of sodium hydroxide in 20 g.
Use the equation: number of moles = mass ÷ relative formula mass.
Answer = ............................ mol [2]
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Worked solution
Number of moles = mass ÷ \(M_r\) = \(20 \div 40 = 0.5\) mol.
Marking scheme
First check the answer on the answer line. If answer = 0.5 (mol) award 2 marks. If answer is incorrect: 1 mark for correct substitution, 20 ÷ 40 (method mark). ALLOW 1/2 or 0.50. ECF for a wrongly stated Mr only if clearly shown. DO NOT ALLOW answers with the wrong unit for the final mark.
Question 27 · Calculation
2 marks
A student dissolves 6.0 g of copper sulfate in water and makes the solution up to a volume of 250 cm\(^3\).
Calculate the concentration of the solution in g/dm\(^3\).
First check the answer on the answer line. If answer = 24 (g/dm3) award 2 marks. If answer is incorrect: 1 mark for converting 250 cm3 to 0.25 dm3 (or 0.250) OR for 6.0 ÷ 0.25. ALLOW 24.0. ALLOW ECF from an incorrect volume conversion for 1 mark if the division is correct. DO NOT ALLOW 0.024 or 1500 without evidence of correct method for 1 mark.
Question 28 · Calculation
2 marks
A student uses paper chromatography to separate the dyes in a green food colouring.
One dye spot travels 3.6 cm from the start line. The solvent travels 9.0 cm from the start line.
Calculate the \(R_f\) value of the dye.
Use the equation: \(R_f\) = distance moved by dye ÷ distance moved by solvent.
Give your answer to 2 decimal places.
\(R_f\) = ............................ [2]
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Worked solution
\(R_f = 3.6 \div 9.0 = 0.40\).
Marking scheme
First check the answer on the answer line. If answer = 0.40 award 2 marks. If answer is incorrect: 1 mark for 3.6 ÷ 9.0 (method mark). ALLOW 0.4 for 1 mark only if 2 d.p. not given AND working is shown; award both marks if 0.4 is given with correct working (AW). DO NOT ALLOW 2.5 (inverted ratio) – award 0 marks.
Question 29 · Calculation
2 marks
A nanoparticle of silver is modelled as a cube with sides of length 4 nm.
(a) Calculate the surface area of the cube.
(b) Calculate the volume of the cube, then the surface area to volume ratio.
Surface area of a cube = 6 × (side length)\(^2\). Volume of a cube = (side length)\(^3\).
Surface area to volume ratio = ............................ : 1 [2]
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Worked solution
Surface area = \(6 \times 4^2 = 96\) nm\(^2\). Volume = \(4^3 = 64\) nm\(^3\). Ratio = \(96 \div 64 = 1.5\), so 1.5 : 1.
Marking scheme
First check the answer on the answer line. If answer = 1.5 (: 1) award 2 marks. If answer is incorrect: 1 mark for either surface area = 96 OR volume = 64 (correct working shown). ALLOW 3/2 or 1.50. ECF from one correct value and a correct division of the candidate's values. IGNORE units.
Question 30 · Calculation
2 marks
A student heats 10.0 g of calcium carbonate in a boiling tube. It breaks down to form calcium oxide and carbon dioxide gas.
The solid left in the tube has a mass of 5.6 g. The carbon dioxide escapes into the air.
Calculate the mass of carbon dioxide produced.
Mass of carbon dioxide = ............................ g [2]
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Worked solution
Mass is conserved, so mass of gas lost = starting mass − final mass = 10.0 − 5.6 = 4.4 g.
Marking scheme
First check the answer on the answer line. If answer = 4.4 (g) award 2 marks. If answer is incorrect: 1 mark for 10.0 − 5.6 (method mark). ALLOW 1 mark for a correct statement that mass is conserved / total mass of products = mass of reactant, if no numerical answer is given. DO NOT ALLOW 15.6 (addition) – award 0 marks.
Question 31 · Calculation
2 marks
A student reacts magnesium ribbon with dilute hydrochloric acid and collects the hydrogen gas in a gas syringe.
The student collects 48 cm\(^3\) of hydrogen in the first 40 seconds.
Calculate the mean rate of reaction over the first 40 seconds.
Use the equation: mean rate = volume of gas ÷ time.
Give your answer to 2 significant figures.
Mean rate = ............................ cm\(^3\)/s [2]
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First check the answer on the answer line. If answer = 1.2 (cm3/s) award 2 marks. If answer is incorrect: 1 mark for 48 ÷ 40 (method mark). ALLOW 1.20 for full marks if working is shown (AW). DO NOT ALLOW 0.83 (inverted) – award 0 marks. Unit must be consistent with cm3/s for the accuracy mark; ALLOW cm3 s-1.
Question 32 · Calculation
2 marks
Hydrogen reacts with chlorine to make hydrogen chloride.
H–H + Cl–Cl → 2 H–Cl
Bond energies in kJ/mol: H–H = 436; Cl–Cl = 243; H–Cl = 432.
The energy needed to break all the bonds in the reactants is 679 kJ/mol.
Calculate the energy released when the bonds in the products are made, and the overall energy change.
Overall energy change = energy to break bonds − energy released making bonds.
Overall energy change = ............................ kJ/mol [2]
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Worked solution
Energy released making 2 H–Cl bonds = 2 × 432 = 864 kJ/mol. Overall energy change = 679 − 864 = −185 kJ/mol (exothermic).
Marking scheme
First check the answer on the answer line. If answer = −185 (kJ/mol) award 2 marks. If answer is incorrect: 1 mark for 864 (energy released making bonds) seen (method mark). ALLOW 185 with the word exothermic or 'released' for full marks (AW). 185 alone with no indication of sign: award 1 mark. ECF from 864 if subtraction is carried out correctly.
Question 33 · Calculation
2 marks
Scientists measure the concentration of carbon dioxide in the atmosphere. In 1800 it was 280 parts per million (ppm). In 2020 it was 420 ppm.
Calculate the percentage increase in the concentration of carbon dioxide between 1800 and 2020.
Use the equation: percentage increase = (increase ÷ original value) × 100.
First check the answer on the answer line. If answer = 50 (%) award 2 marks. If answer is incorrect: 1 mark for 420 − 280 = 140 (method mark). ALLOW 1 mark for 140 ÷ 280 = 0.5 if not converted to a percentage. DO NOT ALLOW 33 (dividing by 420) – award 1 mark for the increase only. ALLOW 50.0.
Question 34 · Short explain / state / suggest
1 marks
Lithium and potassium are both in Group 1 of the Periodic Table.
Explain why lithium and potassium have similar chemical properties. [1]
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Worked solution
Chemical properties depend on the number of outer-shell electrons. Group 1 atoms each have one outer electron, so they react in similar ways.
Marking scheme
1 mark: same number of outer shell electrons / one electron in outer shell (AO1). ALLOW 'same number of electrons in highest energy level'. DO NOT ALLOW 'same number of electrons' or 'same number of shells'.
Question 35 · Short explain / state / suggest
2 marks
Sodium chloride is an ionic compound. It does not conduct electricity when solid but does conduct when molten.
Explain why. [2]
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Worked solution
In solid sodium chloride the charged ions are held in fixed positions in the lattice, so no charge can flow. When molten the ions can move freely and carry the current.
Marking scheme
1 mark: in the solid, ions cannot move / are held in fixed positions (in a lattice). 1 mark: when molten, ions are free to move (and carry charge). DO NOT ALLOW 'electrons move' or 'atoms move'. IGNORE 'ions are free' without reference to molten state.
Question 36 · Short explain / state / suggest
1 marks
Crude oil is a mixture of hydrocarbons that can be separated into fractions.
Name the process used to separate crude oil into fractions. [1]
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Worked solution
Crude oil is heated and its hydrocarbons are separated by boiling point in a fractionating column: fractional distillation.
Marking scheme
1 mark: fractional distillation (AO1). ALLOW fractionation. DO NOT ALLOW 'distillation' alone or 'cracking'.
Question 37 · Short explain / state / suggest
1 marks
A student reacts magnesium ribbon with dilute hydrochloric acid in a flask.
State one change the student could make to increase the rate of reaction without changing the acid. [1]
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Worked solution
Higher temperature or larger surface area of magnesium gives more frequent, more energetic collisions, so a faster rate.
Marking scheme
1 mark: any one from: increase temperature / warm the acid; use magnesium powder or smaller pieces / increase surface area; add a catalyst (AW). DO NOT ALLOW 'use more acid' or 'use more magnesium'.
Question 38 · Short explain / state / suggest
1 marks
Carbon dioxide is a greenhouse gas.
Name one other greenhouse gas. [1]
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Worked solution
Methane and water vapour both absorb and re-emit infrared radiation, contributing to the greenhouse effect.
Marking scheme
1 mark: methane / water vapour (AO1). ALLOW dinitrogen oxide / nitrous oxide / CFCs / ozone. DO NOT ALLOW oxygen, nitrogen, 'carbon monoxide' or 'CO2'.
Question 39 · Short explain / state / suggest
1 marks
A water company adds chlorine to drinking water.
Describe the test for chlorine gas. [1]
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Worked solution
Chlorine is identified by holding damp litmus paper in the gas: it turns red briefly then bleaches white.
Marking scheme
1 mark: damp (blue) litmus paper / indicator paper bleached / turns white. ALLOW 'turns red then white'. DO NOT ALLOW 'dry' litmus paper or 'turns red' only.
Question 40 · Short explain / state / suggest
2 marks
A student mixes two solutions in a polystyrene cup. The temperature rises from 21 °C to 34 °C.
(i) Calculate the temperature change. [1]
(ii) State the type of reaction shown by this temperature change. [1]
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Worked solution
(i) \(34 - 21 = 13\) °C. (ii) The temperature of the surroundings increased, so energy was transferred to them: exothermic.
Marking scheme
(i) 1 mark: 13 (°C). ALLOW 13 without unit; DO NOT ALLOW -13. (ii) 1 mark: exothermic. DO NOT ALLOW 'endothermic'.
Question 41 · Short explain / state / suggest
2 marks
In a scattering experiment, a thin gold foil was bombarded with positively charged particles. Most particles passed straight through, but a very small number bounced back.
Explain what each observation showed about the structure of the atom. [2]
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Worked solution
Most particles were undeflected, so most of the atom is empty space. A few were repelled backwards, so the atom has a tiny, dense, positive centre (the nucleus) containing most of the mass.
Marking scheme
1 mark: most pass through so atom is mostly empty space. 1 mark: some bounce back so there is a small / dense / positively charged nucleus (which repels the particles). IGNORE references to the plum pudding model.
Question 42 · Short explain / state / suggest
2 marks
A technician adds chlorine water to a colourless solution of potassium bromide. The mixture turns orange.
Explain why the solution turns orange. [2]
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Worked solution
Chlorine is higher than bromine in Group 7, so it is more reactive. It displaces bromine from the bromide solution: \( \text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2 \). Bromine in solution is orange.
Marking scheme
Chlorine is more reactive than bromine / chlorine is higher in Group 7 ✓ chlorine displaces bromine (from the potassium bromide) / bromine is formed ✓ ALLOW 'chlorine takes the place of bromine'. DO NOT ALLOW 'chlorine reacts with potassium' alone. IGNORE references to colour alone.
Question 43 · Short explain / state / suggest
2 marks
Solid sodium chloride does not conduct electricity. Molten sodium chloride does conduct electricity.
Explain why. [2]
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Worked solution
Sodium chloride is an ionic compound. In the solid, the ions are held in fixed positions in a lattice, so no charge can flow. When molten the ions are free to move and carry the electric current.
Marking scheme
In the solid, ions are fixed / not free to move / held in a lattice ✓ When molten, ions are free to move (and carry charge) ✓ DO NOT ALLOW 'electrons' move in molten sodium chloride. ALLOW 'ions can move' for second mark. IGNORE 'atoms'.
Question 44 · Short explain / state / suggest
1 marks
Crude oil is a source of hydrocarbons for making fuels and materials.
Explain why crude oil is described as a finite resource. [1]
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Worked solution
Crude oil forms over millions of years, much slower than it is used, so supplies are limited and will eventually run out.
Marking scheme
It will run out / cannot be replaced as fast as it is used / takes millions of years to form ✓ IGNORE 'it is non-renewable' alone. IGNORE 'it is polluting'.
Question 45 · Short explain / state / suggest
2 marks
A student reacts marble chips with dilute hydrochloric acid. She repeats the experiment using the same mass of powdered marble. The powder reacts faster.
Use ideas about particles to explain why. [2]
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Worked solution
Powdered marble has a larger surface area exposed to the acid. More marble particles can collide with acid particles in each second, so there are more frequent successful collisions and the rate is higher.
Marking scheme
Powder has a larger surface area (than chips) ✓ more frequent collisions (between particles) / more collisions per second ✓ ALLOW 'more particles exposed'. DO NOT ALLOW 'more collisions' with no reference to frequency/time as sole answer for second mark if 'more particles' implied is not given. IGNORE 'more energy'.
Question 46 · Short explain / state / suggest
1 marks
Rearing cattle releases a greenhouse gas that is not carbon dioxide.
Name this gas. [1]
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Worked solution
Cattle digestion and waste release methane, a greenhouse gas.
Marking scheme
methane ✓ ALLOW CH4. DO NOT ALLOW 'methene'. IGNORE 'carbon monoxide'.
Question 47 · Short explain / state / suggest
1 marks
A student adds magnesium ribbon to dilute acid in a beaker. The temperature of the mixture rises from \(19.5\,^{\circ}\text{C}\) to \(27.0\,^{\circ}\text{C}\).
Calculate the temperature change. Give your answer in \(^{\circ}\text{C}\). [1]
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Worked solution
\(27.0 - 19.5 = 7.5\,^{\circ}\text{C}\). The temperature rises, so the reaction is exothermic.
Marking scheme
7.5 (°C) ✓ ALLOW +7.5. DO NOT ALLOW -7.5. Answer must show unit or be on a line with unit given.
Question 48 · Short explain / state / suggest
1 marks
Chlorine is added to water at a water treatment works.
State why chlorine is added. [1]
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Worked solution
Chlorination kills microorganisms such as bacteria, making the water safe to drink.
Molten lead bromide is electrolysed using inert electrodes.
Name the product formed at the negative electrode. [1]
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Worked solution
Lead ions (Pb\(^{2+}\)) are positive and move to the negative electrode, where they gain electrons to form lead metal.
Marking scheme
lead ✓ ALLOW Pb. DO NOT ALLOW bromine. DO NOT ALLOW 'lead ions'.
Question 50 · Short explain / state / suggest
2 marks
A technician adds a few drops of bromine water to a test tube of potassium iodide solution. The colourless solution turns brown.
Explain why this reaction happens. Use ideas about the positions of bromine and iodine in Group 7. [2]
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Worked solution
Reactivity decreases down Group 7. Bromine is above iodine, so it is the more reactive halogen. A more reactive halogen displaces a less reactive halogen from a solution of its salt. Iodine is released, giving the brown colour: bromine + potassium iodide -> potassium bromide + iodine.
Marking scheme
Point 1 (1 mark): bromine is more reactive than iodine / bromine is higher up the group. ALLOW iodine is less reactive. DO NOT ALLOW bromine is a stronger element. Point 2 (1 mark): (so) bromine displaces iodine (from potassium iodide) / iodine is formed/released. ALLOW bromine takes the place of iodine. IGNORE bromine reacts with potassium. Contradictions score zero. AO2.1 x2.
Question 51 · Short explain / state / suggest
2 marks
A student reacts 2 g of marble chips with excess dilute hydrochloric acid and measures how fast carbon dioxide is made. The student repeats the experiment with 2 g of powdered marble. All other conditions stay the same. The reaction is faster with the powder.
Explain why, using ideas about particles. [2]
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Worked solution
Powdering the marble breaks it into smaller pieces, increasing the surface area for the same mass. More marble particles are exposed to acid particles, so there are more collisions per second. More frequent successful collisions mean a faster reaction.
Marking scheme
Point 1 (1 mark): powder has a larger surface area (than chips) / more particles exposed. ALLOW greater surface area to volume ratio. Point 2 (1 mark): more frequent collisions (between acid and marble particles) / more collisions per second. ALLOW more chance of collisions. DO NOT ALLOW particles collide with more energy / more particles in total. IGNORE 'more collisions' with no reference to frequency or time only if point 1 is also absent. Contradictions score zero. AO1.1, AO2.1.
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Answer all nine questions in the spaces provided. 90 marks, 1 hour 45 minutes. Questions marked with an asterisk assess quality of extended response.
53 Question · 101.6 marks
Question 1 · Tick-box / true-false
1.9 marks
A student reads about the elements in Group 1 of the Periodic Table.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. Potassium is more reactive than lithium. | ☐ | ☐ | | 2. Sodium reacts with water to produce hydrogen gas. | ☐ | ☐ | | 3. Group 1 metals have higher melting points than most transition metals. | ☐ | ☐ | | 4. Atoms of Group 1 elements each have one electron in their outer shell. | ☐ | ☐ |
[1.9]
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Worked solution
Reactivity increases down Group 1, so potassium is more reactive than lithium (true). Sodium + water gives sodium hydroxide and hydrogen (true). Group 1 metals are soft with low melting points, lower than transition metals (false). Group 1 atoms have one outer electron (true).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. None correct = 0. Only one tick per row; two ticks in a row scores zero for that row (contradiction). AO1.1.
Question 2 · Tick-box / true-false
1.9 marks
Sodium chloride is an ionic compound. Diamond is a giant covalent substance.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. Solid sodium chloride conducts electricity because its ions are free to move. | ☐ | ☐ | | 2. Molten sodium chloride conducts electricity. | ☐ | ☐ | | 3. Diamond has a high melting point because it has many strong covalent bonds. | ☐ | ☐ | | 4. Diamond conducts electricity because it has delocalised electrons. | ☐ | ☐ |
[1.9]
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Worked solution
In solid sodium chloride the ions are fixed in a lattice so it does not conduct (false); when molten the ions can move (true). Diamond's strong covalent bonds need a lot of energy to break (true). In diamond every carbon atom uses all four outer electrons in bonds, so there are no delocalised electrons (false).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. Contradictory ticks in a row score zero for that row. AO1.1, AO1.2.
Question 3 · Tick-box / true-false
1.9 marks
Crude oil is separated into fractions by fractional distillation.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. Crude oil is a mixture of hydrocarbons. | ☐ | ☐ | | 2. Fractions with smaller molecules have higher boiling points. | ☐ | ☐ | | 3. Crude oil is a finite resource. | ☐ | ☐ | | 4. The alkanes have the general formula \( C_nH_{2n+2} \). | ☐ | ☐ |
[1.9]
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Worked solution
Crude oil is a mixture of hydrocarbons (true). Smaller molecules have weaker intermolecular forces so lower boiling points (false). Crude oil formed over millions of years and will run out (true). Alkanes follow \( C_nH_{2n+2} \) (true).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. Contradictory ticks in a row score zero for that row. AO1.1.
Question 4 · Tick-box / true-false
1.9 marks
A student reacts magnesium ribbon with dilute hydrochloric acid and measures how fast hydrogen gas is made.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. Using a more concentrated acid increases the rate of reaction. | ☐ | ☐ | | 2. Using magnesium powder instead of ribbon decreases the rate of reaction. | ☐ | ☐ | | 3. Increasing the temperature makes collisions between particles more frequent and more energetic. | ☐ | ☐ | | 4. A catalyst is used up in the reaction. | ☐ | ☐ |
[1.9]
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Worked solution
Higher concentration means more particles per unit volume so more frequent collisions (true). Powder has a larger surface area so the rate increases (false). Higher temperature gives faster-moving particles, so more frequent and more energetic collisions (true). A catalyst is not used up (false).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. Contradictory ticks in a row score zero for that row. AO1.1, AO2.1.
Question 5 · Tick-box / true-false
1.9 marks
Scientists study carbon dioxide in the atmosphere and the climate.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. Carbon dioxide and methane are greenhouse gases. | ☐ | ☐ | | 2. Burning fossil fuels adds carbon dioxide to the atmosphere. | ☐ | ☐ | | 3. A correlation between two variables proves that one causes the other. | ☐ | ☐ | | 4. Planting new forests can reduce the amount of carbon dioxide in the atmosphere. | ☐ | ☐ |
[1.9]
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Worked solution
Both gases absorb infrared radiation (true). Combustion of carbon-containing fuels forms carbon dioxide (true). Correlation does not prove causation; a plausible mechanism is also needed (false). Growing trees take in carbon dioxide by photosynthesis (true).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. Contradictory ticks in a row score zero for that row. AO1.1, AO2.1.
Question 6 · Tick-box / true-false
1.9 marks
Nanoparticles are used in sun creams and sports equipment.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. Nanoparticles are between 1 nm and 100 nm in size. | ☐ | ☐ | | 2. A cube with sides of 2 cm has a larger surface area to volume ratio than a cube with sides of 1 cm. | ☐ | ☐ | | 3. Graphene is a single layer of carbon atoms. | ☐ | ☐ | | 4. The risks of nanoparticles are all fully known. | ☐ | ☐ |
[1.9]
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Worked solution
Nanoparticles are 1–100 nm (true). The 1 cm cube has ratio \( 6 \div 1 = 6 \) and the 2 cm cube has ratio \( 24 \div 8 = 3 \), so the larger cube has the smaller ratio (false). Graphene is one layer of carbon atoms (true). Long-term risks of nanoparticles are still being researched (false).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. Contradictory ticks in a row score zero for that row. AO1.1, AO2.2.
Question 7 · Tick-box / true-false
1.9 marks
A company carries out a life-cycle assessment (LCA) of a plastic drinks bottle.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. An LCA includes the stages of getting raw materials, manufacture, use and disposal. | ☐ | ☐ | | 2. Recycling a bottle always uses no energy. | ☐ | ☐ | | 3. Putting plastic bottles in landfill uses up land space. | ☐ | ☐ | | 4. Biodegradable materials can be broken down by microorganisms. | ☐ | ☐ |
[1.9]
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Worked solution
LCAs cover raw materials, manufacture, transport, use and disposal (true). Collecting, sorting and reprocessing bottles needs energy (false). Landfill takes up space (true). Biodegradable materials are broken down by microorganisms (true).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. Contradictory ticks in a row score zero for that row. AO1.1.
Question 8 · Tick-box / true-false
1.9 marks
A student electrolyses molten lead bromide using inert electrodes.
Tick (✓) one box in each row to show whether each statement is true or false.
| Statement | True | False | |---|---|---| | 1. Lead is formed at the negative electrode. | ☐ | ☐ | | 2. Bromine is formed at the negative electrode. | ☐ | ☐ | | 3. The lead bromide must be molten so that its ions can move. | ☐ | ☐ | | 4. Positive ions gain electrons during electrolysis. | ☐ | ☐ |
[1.9]
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Worked solution
Positive lead ions move to the negative electrode and gain electrons to form lead (true). Bromine forms at the positive electrode, so statement 2 is false. Ions are free to move only when molten (true). Positive ions are reduced by gaining electrons (true).
Marking scheme
All four rows correct = 1.9 marks. Three correct = 1.4 marks. Two correct = 0.9 marks. One correct = 0.5 marks. Contradictory ticks in a row score zero for that row. AO1.1, AO2.1.
Question 9 · Tick-box / true-false
1.9 marks
A student reads about the halogens (Group 7).
Tick (✓) one box in each row to show whether the statement is true or false.
| Statement | True | False | |---|---|---| | Chlorine is more reactive than bromine. | ☐ | ☐ | | Melting points of the Group 7 elements decrease down the group. | ☐ | ☐ | | Chlorine gas will displace iodine from potassium iodide solution. | ☐ | ☐ |
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Worked solution
Reactivity of Group 7 decreases down the group, so chlorine is more reactive than bromine (true). Melting points increase down the group (false). A more reactive halogen displaces a less reactive halide, so chlorine displaces iodine from potassium iodide (true).
Marking scheme
Row 1 True; Row 2 False; Row 3 True. All three correct = 1.9 marks; two correct = 1.0 mark; one or none correct = 0. Two ticks in a row = row not credited.
Question 10 · Tick-box / true-false
1.9 marks
The table gives the properties of four substances, W, X, Y and Z.
| Substance | Melting point (°C) | Conducts when solid | Conducts when molten | |---|---|---|---| | W | 801 | no | yes | | X | 1085 | yes | yes | | Y | -7 | no | no | | Z | 3550 | no | no |
Tick (✓) two boxes to show which statements are correct.
☐ W has an ionic structure. ☐ X is a simple molecular substance. ☐ Y has a giant covalent structure. ☐ Z has a giant covalent structure. ☐ Z is a metal.
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Worked solution
W has a high melting point and conducts only when molten, so it is ionic. X conducts as a solid and has a high melting point, so it is a metal. Y has a very low melting point and does not conduct, so it is simple molecular. Z has a very high melting point and does not conduct, so it is giant covalent.
Marking scheme
Ticks for: W has an ionic structure (1) and Z has a giant covalent structure (1) - scaled to 1.9 marks in total. Two correct and no incorrect = 1.9; one correct, or two correct with one extra tick = 1.0; otherwise 0. More than two ticks: only the first two marked.
Question 11 · Tick-box / true-false
1.9 marks
A student reacts magnesium ribbon with dilute hydrochloric acid and then repeats the experiment at a higher temperature.
Tick (✓) one box in each row to show whether the statement about the higher temperature is true or false.
| Statement | True | False | |---|---|---| | The particles move faster. | ☐ | ☐ | | There are fewer collisions in each second. | ☐ | ☐ | | A greater proportion of collisions have energy above the activation energy. | ☐ | ☐ | | The activation energy of the reaction decreases. | ☐ | ☐ |
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Worked solution
Raising temperature gives particles more energy so they move faster, collide more often, and a greater proportion of collisions exceed the activation energy. The activation energy itself is unchanged; only a catalyst lowers it.
Marking scheme
True; False; True; False. All four correct = 1.9 marks; three correct = 1.2 marks; two correct = 0.6 marks; fewer = 0. Two ticks in a row = row not credited.
Question 12 · Tick-box / true-false
1.9 marks
Data collected between 1960 and 2020 show that the carbon dioxide concentration in the air rose steadily and the mean global temperature also rose.
Tick (✓) one box in each row to show whether the statement is true or false.
| Statement | True | False | |---|---|---| | Carbon dioxide absorbs infrared radiation emitted from the Earth's surface. | ☐ | ☐ | | The data alone prove that the rise in carbon dioxide caused the temperature rise. | ☐ | ☐ | | Planting new forests can reduce the carbon dioxide concentration in the air. | ☐ | ☐ |
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Worked solution
Greenhouse gases such as carbon dioxide absorb and re-emit infrared radiation. A correlation does not by itself prove causation; a plausible mechanism is also needed. Growing trees take in carbon dioxide by photosynthesis.
Marking scheme
True; False; True. All three correct = 1.9 marks; two correct = 1.0 mark; one or none = 0. Two ticks in a row = row not credited.
Question 13 · Tick-box / true-false
1.9 marks
Molten lead bromide is electrolysed using inert electrodes.
Tick (✓) one box in each row to show whether the statement is true or false.
| Statement | True | False | |---|---|---| | Lead forms at the negative electrode. | ☐ | ☐ | | Bromide ions gain electrons. | ☐ | ☐ | | Solid lead bromide would also conduct electricity in this cell. | ☐ | ☐ |
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Worked solution
Positive lead ions move to the negative electrode and gain electrons to form lead. Bromide ions lose electrons (oxidation) at the positive electrode to form bromine. In solid lead bromide the ions cannot move, so it does not conduct.
Marking scheme
True; False; False. All three correct = 1.9 marks; two correct = 1.0 mark; one or none = 0. Two ticks in a row = row not credited.
Question 14 · Tick-box / true-false
1.9 marks
Water companies treat water from a reservoir to make it potable.
Tick (✓) one box in each row to show whether the statement is true or false.
| Statement | True | False | |---|---|---| | Chlorine is added to kill microorganisms. | ☐ | ☐ | | Filtering through sand and gravel removes dissolved salts. | ☐ | ☐ | | Distillation is used to obtain potable water from sea water. | ☐ | ☐ | | Chlorine gas turns damp blue litmus paper red and then bleaches it. | ☐ | ☐ |
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Worked solution
Chlorination kills microorganisms. Filtration removes only insoluble solids, not dissolved salts. Distillation separates pure water from salt water. Chlorine bleaches damp litmus paper white; it does not turn it red first.
Marking scheme
True; False; True; False. All four correct = 1.9 marks; three correct = 1.2 marks; two correct = 0.6 marks; fewer = 0. Two ticks in a row = row not credited. DO NOT ALLOW answers contradicting the table.
Question 15 · Complete / fill-in / match / label
2 marks
Rubidium is a Group 1 metal. Complete the sentences about Group 1 elements. Use words from the list. Each word may be used once, more than once or not at all.
list: one two seven more less hydrogen oxygen chlorine
(i) Atoms of Group 1 elements have ........ electron in their outer shell. [1] (ii) Rubidium is ........ reactive than sodium. [1]
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Worked solution
Group 1 atoms have one outer electron. Reactivity increases down the group, and rubidium is below sodium, so it is more reactive.
Marking scheme
(i) one [1]. (ii) more [1]. DO NOT ALLOW other words from the list. Contradictions (two words in one gap) score zero for that gap.
Question 16 · Complete / fill-in / match / label
2 marks
Draw lines to connect each substance with the type of structure it has.
Each substance should be connected to one structure. [2]
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Worked solution
Sodium chloride is a metal/non-metal compound forming an ionic lattice. Diamond is a network of carbon atoms joined by covalent bonds. Copper is a metal. Carbon dioxide consists of small covalently bonded molecules.
Marking scheme
All four correct = 2 marks. Three correct = 1 mark. Two or fewer correct = 0 marks. Any substance connected to more than one structure scores no mark for that substance.
Question 17 · Complete / fill-in / match / label
2 marks
Crude oil is separated into fractions by fractional distillation. Complete the sentences. Use words from the list.
(i) The fractions are separated because their molecules have different ........ . [1] (ii) Fractions with the smallest molecules leave the column near the ........ . [1]
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Worked solution
Hydrocarbons in crude oil condense at different temperatures because of their different boiling points. Small molecules have low boiling points so stay as gas longest and leave at the cooler top of the column.
Marking scheme
(i) boiling points [1]. (ii) top [1]. DO NOT ALLOW melting points / densities in (i).
Question 18 · Complete / fill-in / match / label
2 marks
A student adds magnesium ribbon to dilute hydrochloric acid. Complete the sentences about the rate of reaction. Use words from the list.
list: more fewer increases decreases collisions particles activation energy
(i) When the acid is warmed, the particles move faster and there are ........ successful collisions each second. [1] (ii) A catalyst increases the rate of reaction because it lowers the ........ . [1]
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Worked solution
Higher temperature means faster particles, more frequent collisions with enough energy, so more successful collisions per second. A catalyst provides an alternative pathway with a lower activation energy.
Marking scheme
(i) more [1]. (ii) activation energy [1]. DO NOT ALLOW collisions in (ii).
Question 19 · Complete / fill-in / match / label
2 marks
Complete the sentences about climate change. Use words from the list.
(i) Burning ........ increases the concentration of greenhouse gases in the atmosphere. [1] (ii) Greenhouse gases ........ thermal energy radiated from the Earth's surface. [1]
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Worked solution
Fossil fuel combustion releases carbon dioxide. Greenhouse gases absorb infrared radiation from the Earth and re-emit it, warming the atmosphere.
Marking scheme
(i) fossil fuels [1]. (ii) absorb [1]. DO NOT ALLOW reflect in (ii).
Question 20 · Complete / fill-in / match / label
2 marks
Molten lead bromide is electrolysed using inert electrodes. Complete the table to name the product formed at each electrode.
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Worked solution
Positive lead ions move to the negative electrode and gain electrons to form lead metal. Negative bromide ions move to the positive electrode and lose electrons to form bromine.
Marking scheme
Negative electrode: lead [1]. Positive electrode: bromine [1]. ALLOW Pb and Br2. DO NOT ALLOW bromide or hydrogen/oxygen.
Each stage should be connected to one purpose. [2]
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Worked solution
Filtration passes water through beds that trap solids. Chlorine kills microorganisms. Distillation evaporates and condenses the water, leaving the salt behind.
Marking scheme
All three correct = 2 marks. Two correct = 1 mark. One or none correct = 0 marks. A stage connected to more than one purpose scores no mark for that stage.
Question 23 · Complete / fill-in / match / label
2 marks
Potassium reacts with bromine to form the compound potassium bromide, KBr.
Complete the sentences about this reaction. Use words from the list. Each word may be used once, more than once or not at all.
gains loses shares ionic covalent metallic
Each potassium atom ............................ one electron to form a K\(^+\) ion. [1]
The strong attraction between the oppositely charged ions in potassium bromide is called an ............................ bond. [1]
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Worked solution
Potassium is a Group 1 metal, so each atom transfers (loses) its one outer electron to a bromine atom, forming a K\(^+\) ion. Oppositely charged ions in the compound are held together by electrostatic attraction, which is an ionic bond.
Marking scheme
Marks: 2 (1 per correct word, AO1.1).
1. loses [1] - ALLOW 'transfers' / 'gives away'. DO NOT ALLOW 'gains' or 'shares'. 2. ionic [1] - DO NOT ALLOW covalent / metallic.
If more than one word is written in a gap, award zero for that gap (contradiction).
Question 24 · Calculation
2 marks
A technician weighs out 30 g of calcium carbonate, \(CaCO_3\), to use in an antacid experiment.
Calculate the number of moles of calcium carbonate in 30 g.
Relative atomic masses: Ca = 40, C = 12, O = 16.
Give your answer to 2 significant figures. [2]
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Worked solution
Relative formula mass of \(CaCO_3\) = 40 + 12 + (3 × 16) = 100. Moles = mass ÷ relative formula mass = \(30 \div 100 = 0.30\) mol.
Marking scheme
First check the answer on the answer line. If answer = 0.30 (mol) award 2 marks. M1: relative formula mass = 100 (1) M2: \(30 \div 100 = 0.30\) mol (1) ALLOW 0.3 mol. ECF from an incorrect relative formula mass for M2. If Mr is wrong but used correctly, award 1 mark.
Question 25 · Calculation
2 marks
A student dissolves 4.5 g of sodium chloride in water to make 250 cm³ of solution.
Calculate the concentration of the solution in g/dm³.
1 dm³ = 1000 cm³. [2]
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First check the answer on the answer line. If answer = 18 (g/dm³) award 2 marks. M1: converts volume to 0.25 dm³ (1) M2: \(4.5 \div 0.25 = 18\) (1) DO NOT ALLOW 0.018 or 1125 (unit conversion error) for M2, but award M1 if 0.25 is seen. ALLOW ECF.
Question 26 · Calculation
2 marks
A student uses paper chromatography to separate the dyes in a green food colouring. The solvent travels 8.0 cm from the start line. One yellow dye spot travels 3.6 cm from the start line.
Calculate the \(R_f\) value of the yellow dye.
Give your answer to 2 decimal places. [2]
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Worked solution
\(R_f\) = distance moved by dye ÷ distance moved by solvent = \(3.6 \div 8.0 = 0.45\).
Marking scheme
First check the answer on the answer line. If answer = 0.45 award 2 marks. M1: \(3.6 \div 8.0\) (1) M2: 0.45 (1) DO NOT ALLOW 2.2 (inverted ratio) for M2 (M1 not awarded either). ALLOW 0.450.
Question 27 · Calculation
3 marks
Hydrogen reacts with chlorine to make hydrogen chloride.
\(H{-}H + Cl{-}Cl \rightarrow 2\,H{-}Cl\)
Bond energies in kJ/mol: H–H = 436, Cl–Cl = 242, H–Cl = 431.
Calculate the overall energy change for this reaction. Give the sign of your answer and the unit. Then state whether the reaction is exothermic or endothermic. [3]
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Worked solution
Energy to break bonds = 436 + 242 = 678 kJ/mol. Energy released making bonds = 2 × 431 = 862 kJ/mol. Overall change = 678 − 862 = −184 kJ/mol. More energy is released than taken in, so the reaction is exothermic.
Marking scheme
First check the answer on the answer line. If answer = -184 kJ/mol and exothermic award 3 marks. M1: bonds broken = 678 AND bonds made = 862 (1) M2: 678 − 862 = −184 kJ/mol (1) M3: exothermic (1) ALLOW 184 kJ/mol released for M2. ALLOW ECF for M3 from the sign of the calculated answer. If +184 is given, award M1 and M3 only if ECF consistent (endothermic).
Question 28 · Calculation
3 marks
Magnesium burns in oxygen to make magnesium oxide.
\(2Mg(s) + O_2(g) \rightarrow 2MgO(s)\)
Calculate the mass of magnesium oxide made when 6.0 g of magnesium burns completely.
Relative atomic masses: Mg = 24, O = 16. [3]
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Worked solution
Moles of Mg = \(6.0 \div 24 = 0.25\) mol. From the equation, 2 mol Mg gives 2 mol MgO, so moles of MgO = 0.25 mol. Mr of MgO = 24 + 16 = 40. Mass of MgO = \(0.25 \times 40 = 10\) g.
Marking scheme
First check the answer on the answer line. If answer = 10 (g) award 3 marks. M1: moles Mg = \(6.0 \div 24 = 0.25\) (1) M2: moles MgO = 0.25 AND Mr MgO = 40 (1) M3: mass = 0.25 × 40 = 10 g (1) ALLOW alternative ratio method: 48 g Mg gives 80 g MgO, so 6.0 g gives 10 g. ALLOW ECF between steps.
Question 29 · Calculation
2 marks
A nanoparticle of silver is a cube with sides of 20 nm.
Calculate the surface area to volume ratio of the cube.
Surface area of a cube = 6 × (side)². Volume of a cube = (side)³.
Give your answer in the form ___ : 1. [2]
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Worked solution
Surface area = \(6 \times 20^2 = 2400\) nm². Volume = \(20^3 = 8000\) nm³. Ratio = \(2400 \div 8000 = 0.3\), so 0.3 : 1.
Marking scheme
First check the answer on the answer line. If answer = 0.3 : 1 award 2 marks. M1: surface area = 2400 AND volume = 8000 (1) M2: \(2400 \div 8000 = 0.3\) : 1 (1) ALLOW 0.30 : 1. ALLOW 3 : 10 for M2. IGNORE units.
Question 30 · Short explain / describe / state
1 marks
Potassium and sodium are both Group 1 metals. State how the reactivity of potassium with water compares with the reactivity of sodium with water. [1]
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Worked solution
Reactivity increases down Group 1. Potassium is below sodium, so its outer electron is lost more easily and it reacts more vigorously with water.
Marking scheme
1 mark: potassium is more reactive / reacts faster / more vigorously than sodium. ALLOW 'sodium less reactive'. DO NOT ALLOW 'potassium is reactive' with no comparison.
Question 31 · Short explain / describe / state
2 marks
Sodium chloride has a giant ionic lattice. Explain why solid sodium chloride does not conduct electricity but molten sodium chloride does. [2]
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Worked solution
In solid sodium chloride the ions are held in fixed positions by strong electrostatic forces, so no charged particles can move. When molten, the lattice breaks down and the ions can move, carrying the electric current.
Marking scheme
1 mark: in the solid, ions are fixed in position / cannot move. 1 mark: when molten, ions are free to move (and carry charge / current). DO NOT ALLOW 'electrons' move in molten sodium chloride. IGNORE 'atoms'.
Question 32 · Short explain / describe / state
2 marks
A student reacts marble chips with dilute hydrochloric acid. She repeats the experiment using the same mass of powdered marble. The powdered marble reacts faster. Explain why, using ideas about particles. [2]
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Worked solution
Powdering the marble increases its surface area exposed to the acid. More acid particles can collide with marble particles each second, so the frequency of successful collisions increases and the rate rises.
Marking scheme
1 mark: powder has a larger surface area (exposed to the acid). 1 mark: more frequent collisions between particles / more collisions per second. ALLOW 'more successful collisions'. DO NOT ALLOW 'collisions have more energy'.
Question 33 · Short explain / describe / state
1 marks
Crude oil is separated into fractions by fractional distillation. State one reason why fractions with short hydrocarbon molecules are collected near the top of the fractionating column. [1]
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Worked solution
Short molecules have weaker intermolecular forces and so lower boiling points. They rise furthest up the column before condensing in the cooler region.
Marking scheme
1 mark: short molecules have low(er) boiling points / condense at lower temperatures / the column is cooler at the top. ALLOW 'weaker intermolecular forces' . IGNORE 'lighter' alone.
Question 34 · Short explain / describe / state
2 marks
When a student mixes two solutions in a polystyrene cup, the temperature of the mixture rises from 21 °C to 29 °C. State whether the reaction is exothermic or endothermic and explain how you can tell. [2]
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Worked solution
A temperature rise means energy is released to the surroundings, which is characteristic of an exothermic reaction.
Marking scheme
1 mark: exothermic. 1 mark: temperature increased / energy transferred to the surroundings (the solution). The second mark can only be awarded if exothermic is stated. DO NOT ALLOW 'heat is made'.
Question 35 · Short explain / describe / state
1 marks
Carbon dioxide is a greenhouse gas. Describe what happens to the thermal (infrared) radiation from the Earth's surface when it meets carbon dioxide in the atmosphere. [1]
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Worked solution
Greenhouse gases absorb infrared radiation and re-radiate it, some of it back to the surface, which keeps the lower atmosphere warmer.
Marking scheme
1 mark: absorbed (and re-emitted / radiated back towards Earth). ALLOW 'trapped' . DO NOT ALLOW 'reflects UV' or 'ozone layer' ideas.
Question 36 · Short explain / describe / state
1 marks
A chemist measures the melting point of a solid sample. The sample melts over a range of 118 °C to 124 °C. The pure compound melts sharply at 130 °C. What do these results tell you about the sample? [1]
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Worked solution
Impure substances melt over a range of temperatures and below the melting point of the pure substance.
Marking scheme
1 mark: the sample is impure / contains other substances. ALLOW 'not pure'. DO NOT ALLOW 'the sample is a mixture of elements'.
Question 37 · Short explain / describe / state
1 marks
Silver nanoparticles are added to some socks. A nanoparticle has a diameter of 40 nm. State why this particle is classed as a nanoparticle. [1]
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Worked solution
Nanoparticles have dimensions in the range 1–100 nm; 40 nm lies within this range.
Marking scheme
1 mark: 40 nm is between 1 and 100 nm / within the range 1–100 nm. ALLOW 'less than 100 nm' if 1 nm lower limit is not contradicted.
Question 38 · Short explain / describe / state
2 marks
A student adds small pieces of lithium and potassium to separate bowls of water. Potassium reacts more vigorously than lithium.
Explain why potassium is more reactive than lithium. [2]
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Worked solution
Both are Group 1 metals and react by losing one outer electron. Potassium has more electron shells, so its outer electron is further from the nucleus and less strongly held, so it is lost more easily.
Marking scheme
1 mark: potassium's outer electron is further from the nucleus / potassium atoms have more shells. 1 mark: so the outer electron is held less strongly / lost more easily. ALLOW weaker attraction between nucleus and outer electron. DO NOT ALLOW 'potassium is bigger so it is more reactive' alone. IGNORE references to the number of outer electrons being different.
Question 39 · Short explain / describe / state
2 marks
Magnesium oxide is an ionic compound. It does not conduct electricity when solid but it does conduct when molten.
Explain why. [2]
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Worked solution
In the solid lattice the ions are held in fixed positions. When molten the lattice breaks down and the ions can move, carrying the electric charge.
Marking scheme
1 mark: in the solid the ions cannot move / are held in fixed positions. 1 mark: when molten the ions are free to move (and carry charge). DO NOT ALLOW 'electrons move' or 'atoms move'. ALLOW 'ions are mobile when molten'.
Question 40 · Short explain / describe / state
2 marks
A student reacts marble chips with dilute hydrochloric acid. The reaction is faster when the same mass of marble is crushed into a powder.
Explain why, using ideas about particles. [2]
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Worked solution
Crushing increases the surface area exposed to the acid, so there are more frequent collisions between reacting particles, increasing the rate.
Marking scheme
1 mark: powder has a larger surface area (exposed). 1 mark: more frequent / more successful collisions per second. DO NOT ALLOW 'more collisions' with no link to time or frequency unless clearly comparative. IGNORE 'more energy'.
Question 41 · Short explain / describe / state
1 marks
State one human activity that increases the amount of carbon dioxide in the atmosphere. [1]
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Worked solution
Burning coal, oil or gas releases carbon dioxide; cutting down forests removes trees that absorb it.
Marking scheme
1 mark for one of: burning fossil fuels / coal / oil / gas; deforestation; ALLOW burning petrol in cars, power stations. DO NOT ALLOW 'pollution' or 'factories' alone.
Question 42 · Short explain / describe / state
1 marks
A sample of a solid melts gradually between 118 °C and 125 °C. The pure compound melts at exactly 130 °C.
What does this tell you about the sample? [1]
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Worked solution
Impurities lower the melting point and make the substance melt over a range of temperatures, so the sample is not pure.
Marking scheme
1 mark: the sample is impure / contains other substances. ALLOW 'not pure'. DO NOT ALLOW 'it is a different compound' alone.
Question 43 · Short explain / describe / state
1 marks
Name the substance added to drinking water to kill microorganisms. [1]
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Worked solution
Chlorination is the stage of water treatment that kills microorganisms.
Marking scheme
1 mark: chlorine. ALLOW chlorine compounds / chlorine gas / chlorination. DO NOT ALLOW chloride.
Question 44 · Short explain / describe / state
1 marks
Sodium hydroxide, NaOH, has a relative formula mass of 40.
Calculate the number of moles in 8.0 g of sodium hydroxide. Give your answer to 2 significant figures. [1]
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Worked solution
Moles = mass / relative formula mass = \( 8.0 \div 40 = 0.20 \) mol.
Marking scheme
Answer on the answer line 0.20 (mol) = 1 mark. ALLOW 0.2 mol. Unit mol required for the mark.
Question 45 · Short explain / describe / state
1 marks
A student mixes two solutions in a polystyrene cup. The temperature rises from 21 °C to 29 °C.
State what this shows about the type of reaction. [1]
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Worked solution
A temperature rise means energy is released to the surroundings, so the reaction is exothermic.
Marking scheme
1 mark: exothermic / energy transferred to the surroundings. DO NOT ALLOW endothermic. IGNORE 'heat is made'.
Question 46 · Short explain / describe / state
2 marks
A technician places a small piece of lithium into a trough of water.
State two observations the technician would make. [2]
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Worked solution
Lithium is a Group 1 metal. It reacts with water to form lithium hydroxide and hydrogen gas, so bubbles are seen and the metal floats, moves and shrinks.
Marking scheme
Any two from: fizzing / bubbles / gas produced (1); lithium floats / moves on the surface (1); lithium gets smaller / disappears / dissolves (1). ALLOW universal indicator turns purple/blue if indicator stated. DO NOT ALLOW 'hydrogen is produced' as an observation. IGNORE 'reacts with water'. Max 2 marks.
Question 47 · Short explain / describe / state
2 marks
Sodium chloride has a giant ionic lattice structure.
Explain why sodium chloride conducts electricity when molten but not when solid. [2]
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Worked solution
Conduction needs charged particles that can move. In the solid lattice the ions are fixed in place by strong electrostatic forces. When molten the lattice breaks down and the ions can move.
Marking scheme
Molten: ions are free to move / mobile (1). Solid: ions are in fixed positions / cannot move (1). ALLOW ions can carry the charge/current. DO NOT ALLOW 'electrons move' or 'atoms move'. IGNORE references to melting point.
Question 48 · Short explain / describe / state
2 marks
A student reacts marble chips with dilute hydrochloric acid. She then repeats the experiment using the same mass of powdered marble. Everything else stays the same.
Explain why the reaction with powdered marble is faster. [2]
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Worked solution
Powdering the marble exposes more particles to the acid. More collisions happen each second, so the rate increases.
Marking scheme
Powder has a larger (surface area) / more particles exposed (1); more frequent / more collisions (between particles) per second (1). ALLOW greater chance of collisions. DO NOT ALLOW 'more energetic collisions'. IGNORE 'powder is smaller' alone.
Question 49 · Short explain / describe / state
1 marks
Chlorine is added to water at a water treatment works.
State why chlorine is added. [1]
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Worked solution
Chlorination disinfects the water so that it is safe to drink.
Marking scheme
Kills bacteria / microorganisms / microbes / pathogens (1). ALLOW sterilise / disinfect. DO NOT ALLOW 'removes dirt', 'removes solids' or 'purifies' alone.
Question 50 · Short explain / describe / state
1 marks
Burning fossil fuels increases the amount of carbon dioxide in the atmosphere.
Suggest one way of reducing the amount of carbon dioxide released into the atmosphere. [1]
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Worked solution
Any method that cuts fossil-fuel burning, removes carbon dioxide from emissions, or absorbs carbon dioxide from the air reduces the amount in the atmosphere.
Marking scheme
Any one from: use renewable energy sources / less fossil fuel (1); plant more trees / reforestation (1); carbon capture and storage (1). Max 1 mark. IGNORE 'stop pollution' and 'recycle'.
Question 51 · Short explain / describe / state
1 marks
A student mixes two solutions in a polystyrene cup. The temperature of the mixture rises from 21 \(^\circ\)C to 34 \(^\circ\)C.
State what type of reaction this shows and give a reason for your answer. [1]
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Worked solution
A rise in temperature means energy is released to the surroundings, which is an exothermic reaction.
Marking scheme
Exothermic AND temperature increases / energy given out to surroundings (1). Both parts needed. DO NOT ALLOW endothermic. DO NOT ALLOW 'heat is made'.
Question 52 · Extended response (level of response)
6 marks
*A student investigates how the rate of reaction between marble chips (calcium carbonate) and dilute hydrochloric acid changes with temperature. The reaction produces carbon dioxide gas.
The student has a conical flask, a gas syringe, a stopwatch, a thermometer, a water bath, marble chips of the same size, and dilute hydrochloric acid.
Describe a method the student could use to find out how temperature affects the rate of this reaction. Explain, using ideas about particles, the results the student should expect.
Include in your answer: - how the rate is measured - what the student should keep constant - the expected results and an explanation using particles.
[6]
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Worked solution
Method: Measure a fixed volume of dilute hydrochloric acid into a conical flask and warm it in a water bath to a chosen temperature (e.g. 20, 30, 40, 50, 60 °C), checking with a thermometer. Add a fixed mass of marble chips, quickly connect the gas syringe and start the stopwatch. Record the volume of carbon dioxide collected after a set time (e.g. 60 s), or the time taken to collect a set volume. Repeat at each temperature. Keep constant: mass and size of marble chips, volume and concentration of acid. Expected results: the higher the temperature, the more gas collected in the same time (faster rate). Explanation: at higher temperature the particles have more kinetic energy and move faster, so they collide more often and more of the collisions have energy at least equal to the activation energy, so there are more successful collisions per second.
Marking scheme
Level 3 (5-6 marks): A complete, logically ordered answer with a method that would work (gas volume in fixed time or time for fixed volume, several temperatures), at least two correct control variables, the correct trend AND a particle explanation covering both more frequent collisions and more energetic/successful collisions. Level 2 (3-4 marks): A reasonable method with at least one control variable or a trend, with a partial particle explanation (e.g. only 'particles move faster / more collisions'); some detail may be missing. Level 1 (1-2 marks): Simple statements, e.g. 'use a stopwatch and heat the acid' or 'it goes faster when hot', with little or no ordering or particle ideas. Level 0 (0 marks): No creditable response. Indicative content: measure gas volume in a set time / time to collect a set volume; at least 5 temperatures; thermometer/water bath; repeat for reliability; keep constant mass and size of marble chips, volume and concentration of acid; higher temperature gives faster rate; particles have more energy and move faster; more frequent collisions; greater proportion of collisions have energy above activation energy (more successful collisions). ALLOW: measuring mass loss on a balance instead of a gas syringe; AW for 'successful collisions'. DO NOT ALLOW: 'particles expand'; 'more particles' at higher temperature; 'activation energy decreases'. IGNORE: references to the reaction becoming exothermic/endothermic. AO1.1 x2, AO2.1 x2, AO3.3b x2.
Question 53 · Extended response (level of response)
6 marks
*Table 2.1 shows some properties of three substances, P, Q and R.
Table 2.1
| Substance | Melting point in °C | Conducts electricity when solid | Conducts electricity when molten | |---|---|---|---| | P | 801 | no | yes | | Q | 1085 | yes | yes | | R | -7 | no | no |
One of the substances is sodium chloride, one is copper and one is bromine.
A student says: 'The bonding in a substance decides its properties.'
Use the information in Table 2.1 to decide which substance is which. Explain how the type of bonding and structure in each substance accounts for its melting point and its electrical conductivity.
[6]
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Worked solution
P conducts only when molten and has a high melting point, so it is an ionic compound: sodium chloride. In the solid the ions are held in fixed positions in the lattice, so cannot carry charge; when molten they are free to move. Strong electrostatic forces between oppositely charged ions need a lot of energy to overcome. Q conducts when solid and molten and has a high melting point, so it is a metal: copper. It has positive ions in a sea of delocalised electrons; the electrons are free to move and carry charge, and the strong metallic bonding gives a high melting point. R has a low melting point and does not conduct: it is bromine, made of simple covalent molecules. The weak intermolecular forces between molecules are easily overcome (the covalent bonds inside the molecules do not break), and there are no free electrons or ions to carry charge.
Marking scheme
Level 3 (5-6 marks): All three substances correctly identified AND a clear explanation of both melting point and conductivity for at least two substances, with correct reference to ions/delocalised electrons/intermolecular forces for all three, with a logical line of reasoning. Level 2 (3-4 marks): Most substances identified; explanations given for melting point and/or conductivity for at least two substances, though some detail missing or one idea confused. Level 1 (1-2 marks): Some correct identification or simple statements about bonding or properties, with little explanation. Level 0 (0 marks): No creditable response. Indicative content: P = NaCl, Q = Cu, R = Br2. P: giant ionic lattice; strong electrostatic forces between oppositely charged ions; high melting point; ions fixed in solid so no conduction; ions free to move when molten. Q: metallic bonding; positive ions and delocalised electrons; strong attraction so high melting point; delocalised electrons carry charge in solid and liquid. R: simple molecular; weak intermolecular forces; low melting point; no free charged particles. DO NOT ALLOW: 'covalent bonds break' when R melts; 'electrons move in ionic compound'; 'atoms' for ions in P. ALLOW: AW for delocalised electrons ('free electrons'). IGNORE: references to the student's statement alone. AO1.1 x2, AO2.1 x2, AO3.1a x2.
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