An original Thinka practice paper modelled on the structure and difficulty of the Jun 2025 (V3) Cambridge IGCSE Science - Combined (0653) paper. Not affiliated with or reproduced from Cambridge.
Paper 23 (選擇題)
Answer all forty questions on the multiple choice answer sheet.
36 题目 · 36 分
题目 1 · 選擇題
1 分
Strips of plant tissue are immersed in a concentrated sucrose solution for two hours. Which row correctly identifies the net direction of water movement and the resulting state of the plant cells?
A.net movement into the cells ; cells become turgid
B.net movement into the cells ; cells burst
C.net movement out of the cells ; cells become plasmolysed
D.net movement out of the cells ; cells burst overcome by internal pressure pressure internal by overcome burst cells ; cells the out of movement net cells burst overcome by internal pressure
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解题
In a concentrated sucrose solution, the water potential outside the plant cell is lower than inside the cell cytoplasm/vacuole. Water moves out of the cells down a water potential gradient by osmosis. This loss of turgor pressure causes the cytoplasm to pull away from the cell wall, making the cells plasmolysed.
评分标准
C ; [1 mark]
题目 2 · 選擇題
1 分
Four identical cylinders of potato tissue, each with an initial mass of \(5.0\text{ g}\), are placed into four separate sucrose solutions of different concentrations. After two hours, the cylinders are removed, blotted dry, and reweighed. Which final mass corresponds to the potato cylinder placed in the solution with the lowest water potential?
A.\(5.8\text{ g}\)
B.\(5.3\text{ g}\)
C.\(4.9\text{ g}\)
D.\(4.2\text{ g}\)
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解题
A solution with the lowest water potential is the most concentrated solution. Water moves out of the potato cells into the solution by osmosis down a water potential gradient (from higher water potential inside the cells to lower water potential outside). This results in the greatest loss of mass, giving the lowest final mass of \(4.2\text{ g}\).
评分标准
D [1]
题目 3 · 選擇題
1 分
A chromatogram of a sample contains a dye that travels a distance of \(6.0\text{ cm}\) from the baseline. The solvent front travels a distance of \(8.0\text{ cm}\) from the baseline. What is the \(R_\text{f}\) value of this dye?
A.\(0.25\)
B.\(0.60\)
C.\(0.75\)
D.\(1.33\)
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解题
The retention factor \(R_\text{f}\) is calculated using the formula: \(R_\text{f} = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent front}} = \frac{6.0\text{ cm}}{8.0\text{ cm}} = 0.75\).
评分标准
C [1]
题目 4 · 選擇題
1 分
Why do solid metals conduct thermal energy much more rapidly than non-metallic solids such as plastics?
A.Metals contain delocalised electrons that transfer energy rapidly through the structure.
B.Metals expand much less than plastics when their temperature increases.
C.Metal atoms are able to move freely from the hot region to the cold region.
D.Metal atoms vibrate with lower frequencies than atoms in non-metals.
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解题
In metals, thermal conduction occurs both via lattice vibrations and via delocalised (free) electrons that move quickly through the structure, transferring kinetic energy much faster than the atomic vibration mechanism alone.
评分标准
A [1]
题目 5 · 選擇題
1 分
Which row correctly identifies the type of reaction that occurs when ethene is bubbled into aqueous bromine and the colour change observed?
A.addition; brown to colourless
B.addition; colourless to brown
C.substitution; brown to colourless
D.substitution; colourless to brown
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解题
Ethene is an unsaturated hydrocarbon containing a carbon-carbon double bond (\(\text{C}=\text{C}\)). It undergoes an addition reaction with aqueous bromine, breaking the double bond to form 1,2-dibromoethane. This causes the aqueous bromine to change colour from brown (or orange-brown) to colourless.
评分标准
A [1]
题目 6 · 選擇題
1 分
A toy vehicle of mass \(0.40\text{ kg}\) travels along a flat surface at a constant speed of \(3.0\text{ m/s}\). What is the kinetic energy of the vehicle?
A.\(0.60\text{ J}\)
B.\(1.2\text{ J}\)
C.\(1.8\text{ J}\)
D.\(3.6\text{ J}\)
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解题
Kinetic energy is given by \(E_k = \frac{1}{2}mv^2\). Substituting the values: \(E_k = \frac{1}{2} \times 0.40\text{ kg} \times (3.0\text{ m/s})^2 = 0.20 \times 9.0 = 1.8\text{ J}\).
评分标准
C [1]
题目 7 · 選擇題
1 分
A student places two identical cylinders of fresh potato tissue into two separate sucrose solutions, X and Y.
After 60 minutes: • the potato cylinder in solution X has increased in mass and is firm • the potato cylinder in solution Y has decreased in mass and is limp.
Which row correctly identifies the water potential of each solution compared to the potato cells?
A.solution X: higher water potential; solution Y: lower water potential
B.solution X: higher water potential; solution Y: higher water potential
C.solution X: lower water potential; solution Y: higher water potential
D.solution X: lower water potential; solution Y: lower water potential
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解题
In solution X, water enters the potato cells by osmosis down a water potential gradient, causing an increase in mass and turgidity. Therefore, solution X has a higher water potential than the potato cells. In solution Y, water leaves the potato cells by osmosis, causing a decrease in mass and flaccidity. Therefore, solution Y has a lower water potential than the potato cells.
评分标准
A is correct [1]; B, C, and D describe incorrect combinations of relative water potentials.
题目 8 · 選擇題
1 分
A student carries out two chemical tests on a solid substance, W.
1. Dilute hydrochloric acid is added to solid W. Effervescence is observed, and the gas given off turns limewater cloudy. 2. Solid W is dissolved in water to form an aqueous solution. When aqueous sodium hydroxide is added dropwise, a light blue precipitate is formed.
What is solid W?
A.copper(II) carbonate
B.copper(II) sulfate
C.iron(II) carbonate
D.iron(II) sulfate
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解题
The reaction with dilute hydrochloric acid produces carbon dioxide gas (which turns limewater milky/cloudy), indicating the presence of carbonate ions (\(\text{CO}_3^{2-}\)). The addition of aqueous sodium hydroxide produces a light blue precipitate insoluble in excess, confirming the presence of copper(II) ions (\(\text{Cu}^{2+}\)). Thus, solid W is copper(II) carbonate.
评分标准
A is correct [1]; B lacks carbonate; C and D contain iron(II) which gives a green precipitate.
题目 9 · 選擇題
1 分
A rigid, sealed metal cylinder contains a fixed mass of gas. The gas is heated from \(20^\circ\text{C}\) to \(80^\circ\text{C}\).
What happens to the average kinetic energy of the gas particles and the pressure exerted by the gas inside the cylinder?
B.average kinetic energy: increases; pressure: stays the same
C.average kinetic energy: stays the same; pressure: increases
D.average kinetic energy: stays the same; pressure: stays the same
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解题
Heating increases the temperature of the gas, which directly increases the average kinetic energy and speed of the gas particles. Since the volume of the rigid cylinder is fixed, the faster-moving particles collide more frequently and with greater force against the inner walls of the container, leading to an increase in pressure.
评分标准
A is correct [1]; B, C, and D incorrectly state that kinetic energy or pressure remains constant.
题目 10 · 選擇題
1 分
Which statement correctly describes the homologous series of alkanes?
A.They are unsaturated hydrocarbons that decolourise aqueous bromine.
B.Their boiling points decrease as the number of carbon atoms per molecule increases.
C.They are saturated hydrocarbons with the general formula \(\text{C}_n\text{H}_{2n+2}\).
D.They react with steam in the presence of an acid catalyst to produce alcohols.
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解题
Alkanes are saturated hydrocarbons with the general formula \(\text{C}_n\text{H}_{2n+2}\). Their boiling points increase (not decrease) with increasing carbon chain length due to stronger intermolecular forces. Alkenes, not alkanes, decolourise aqueous bromine and react with steam to form alcohols.
评分标准
C is correct [1]; A and D describe alkenes; B states the reverse of the boiling point trend.
题目 11 · 選擇題
1 分
An electric crane lifts a shipping crate of weight \(400\text{ N}\) vertically through a height of \(3.0\text{ m}\) in \(6.0\text{ s}\).
What is the useful power output of the crane?
A.\(200\text{ W}\)
B.\(800\text{ W}\)
C.\(1200\text{ W}\)
D.\(7200\text{ W}\)
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解题
Useful work done \(W = F \times d = 400\text{ N} \times 3.0\text{ m} = 1200\text{ J}\). Useful power output \(P = \frac{W}{t} = \frac{1200\text{ J}}{6.0\text{ s}} = 200\text{ W}\).
评分标准
A is correct [1]; B is calculated by dividing work by an incorrect factor; C is total work done (1200 J) without dividing by time; D is \(400 \times 3.0 \times 6.0\).
题目 12 · 選擇題
1 分
A student adds aqueous sodium hydroxide dropwise to an unknown aqueous salt solution until in excess. A light blue precipitate forms which does not dissolve in excess sodium hydroxide.
Which cation is present in the solution?
A.\(\text{Cu}^{2+}\)
B.\(\text{Fe}^{2+}\)
C.\(\text{Fe}^{3+}\)
D.\(\text{Zn}^{2+}\)
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解题
Copper(II) ions, \(\text{Cu}^{2+}\), react with aqueous sodium hydroxide to form a light blue precipitate of copper(II) hydroxide, \(\text{Cu(OH)}_2\), which is insoluble in excess sodium hydroxide. Iron(II) gives a green precipitate, iron(III) gives a red-brown precipitate, and zinc gives a white precipitate that dissolves in excess.
评分标准
A [1]
题目 13 · 選擇題
1 分
A metal saucepan containing cold water is placed on a hot electric hotplate.
Which row correctly identifies the primary method of thermal energy transfer through the solid base of the saucepan and throughout the water?
A.through the base: conduction ; throughout the water: convection
B.through the base: conduction ; throughout the water: radiation
C.through the base: convection ; throughout the water: conduction
D.through the base: radiation ; throughout the water: convection
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解题
Thermal energy transfer through solids (such as the metal base of a saucepan) occurs primarily via conduction due to lattice vibrations and free electron diffusion. Thermal energy transfer throughout fluids (such as liquid water) occurs primarily via convection currents caused by changes in density upon heating.
评分标准
A [1]
题目 14 · 選擇題
1 分
A cylinder of fresh potato tissue with an initial mass of \(5.0\text{ g}\) is immersed in a concentrated sucrose solution for two hours.
Which statement correctly describes the change in mass of the potato tissue and the reason for this change?
A.The final mass is greater than \(5.0\text{ g}\) because water enters the cells by osmosis.
B.The final mass is greater than \(5.0\text{ g}\) because sucrose enters the cells by active transport.
C.The final mass is less than \(5.0\text{ g}\) because water leaves the cells by osmosis.
D.The final mass is less than \(5.0\text{ g}\) because sucrose leaves the cells by diffusion.
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解题
The concentrated sucrose solution has a lower water potential than the cytoplasm inside the potato cells. Therefore, water moves out of the potato cells by osmosis down a water potential gradient, causing a decrease in tissue mass (mass becomes less than 5.0 g).
评分标准
C [1]
题目 15 · 選擇題
1 分
A gaseous hydrocarbon rapidly turns aqueous bromine from orange-brown to colourless.
Which statement about this hydrocarbon is correct?
A.It is an alkane containing only single covalent bonds.
B.It is an alkene containing a carbon-carbon double bond.
C.It is a saturated compound that cannot undergo addition reactions.
D.It has the molecular formula \(\text{C}_2\text{H}_6\).
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解题
Decolorisation of aqueous bromine is the standard chemical test for unsaturation (alkenes). Alkenes contain at least one carbon-carbon double bond (\(\text{C}=\text{C}\)) and undergo addition reactions. Alkanes are saturated (single bonds only) and do not rapidly decolourise bromine water in the dark.
评分标准
B [1]
题目 16 · 選擇題
1 分
A model vehicle of mass \(0.50\text{ kg}\) accelerates uniformly along a straight horizontal track from rest to a speed of \(4.0\text{ m/s}\) in \(2.0\text{ s}\).
What is the resultant force acting on the vehicle?
A.\(0.25\text{ N}\)
B.\(1.0\text{ N}\)
C.\(2.0\text{ N}\)
D.\(4.0\text{ N}\)
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解题
First calculate the acceleration: \(a = \frac{\Delta v}{t} = \frac{4.0\text{ m/s} - 0\text{ m/s}}{2.0\text{ s}} = 2.0\text{ m/s}^2\). Then apply Newton's second law: \(F = m \times a = 0.50\text{ kg} \times 2.0\text{ m/s}^2 = 1.0\text{ N}\).
评分标准
B [1]
题目 17 · 選擇題
1 分
A student carries out paper chromatography on a sample of food colouring. The distance moved by the solvent front from the baseline is \(8.0\text{ cm}\). A blue dye present in the mixture travels a distance of \(5.2\text{ cm}\) from the baseline. What is the \(R_f\) value of the blue dye?
A.0.35
B.0.65
C.1.54
D.2.80
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解题
The retention factor (\(R_f\)) is calculated using the formula: \(R_f = \frac{\text{distance moved by substance}}{\text{distance moved by solvent front}} = \frac{5.2\text{ cm}}{8.0\text{ cm}} = 0.65\).
评分标准
B ; [1]
题目 18 · 選擇題
1 分
Four identical metal cans are filled with equal volumes of boiling water at \(100^\circ\text{C}\). Each can has a different outer surface coating. Which can cools down most rapidly by emitting thermal radiation?
A.dull black surface
B.shiny black surface
C.dull white surface
D.shiny white surface
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解题
A dull, black surface is the best emitter of thermal radiation. Therefore, the can with a dull black coating emits infrared radiation at the fastest rate and cools down most rapidly.
评分标准
A ; [1]
题目 19 · 選擇題
1 分
An electric toy car of mass \(0.50\text{ kg}\) accelerates from rest to a constant speed of \(4.0\text{ m/s}\). What is the kinetic energy of the car when it is travelling at \(4.0\text{ m/s}\)?
A.\(1.0\text{ J}\)
B.\(2.0\text{ J}\)
C.\(4.0\text{ J}\)
D.\(8.0\text{ J}\)
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解题
Kinetic energy is given by \(E_k = \frac{1}{2}mv^2\). Substituting the given values: \(E_k = \frac{1}{2} \times 0.50\text{ kg} \times (4.0\text{ m/s})^2 = 0.25 \times 16 = 4.0\text{ J}\).
评分标准
C ; [1]
题目 20 · 選擇題
1 分
Which statement correctly describes the cracking of long-chain alkanes?
A.It is an addition reaction that forms only short-chain alkanes.
B.It is a thermal decomposition reaction that produces short-chain alkanes and alkenes.
C.It is an oxidation reaction that produces carbon dioxide and water.
D.It is a substitution reaction that produces polymers.
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解题
Cracking is a thermal decomposition process in which large, less useful alkane molecules are broken down at high temperatures into smaller alkanes and alkenes.
评分标准
B ; [1]
题目 21 · 選擇題
1 分
Strips of plant tissue of equal initial size are placed into sucrose solutions of different concentrations: \(0.1\text{ mol/dm}^3\), \(0.3\text{ mol/dm}^3\), \(0.5\text{ mol/dm}^3\), and \(0.7\text{ mol/dm}^3\). The water potential of the plant cell sap is equal to that of a \(0.3\text{ mol/dm}^3\) sucrose solution. In which sucrose solution will the plant cells become turgid?
A.\(0.1\text{ mol/dm}^3\)
B.\(0.3\text{ mol/dm}^3\)
C.\(0.5\text{ mol/dm}^3\)
D.\(0.7\text{ mol/dm}^3\)
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解题
A \(0.1\text{ mol/dm}^3\) sucrose solution has a higher water potential than the cell sap (\(0.3\text{ mol/dm}^3\)). Therefore, water enters the cells by osmosis down a water potential gradient, causing them to swell and become turgid.
评分标准
A ; [1]
题目 22 · 選擇題
1 分
Strips of plant tissue are placed in a concentrated sucrose solution for two hours. Which row correctly describes the net movement of water and the state of the plant cells?
A.Net movement of water: into the cells by osmosis | State of cells: turgid
B.Net movement of water: into the cells by active transport | State of cells: flaccid
C.Net movement of water: out of the cells by osmosis | State of cells: plasmolysed
D.Net movement of water: out of the cells by diffusion | State of cells: turgid
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解题
In a concentrated sucrose solution, the water potential outside the plant cell is lower than inside the cell cytoplasm/vacuole. Water leaves the cell by osmosis down a water potential gradient. As water leaves, the cytoplasm shrinks away from the cell wall, causing the cells to become plasmolysed (or flaccid).
评分标准
C is correct [1]. Net movement of water out of cells down water potential gradient via osmosis leads to plasmolysis.
题目 23 · 選擇題
1 分
An unknown solid ionic salt is dissolved in distilled water. The following tests are carried out on separate portions of the solution:
1. Aqueous sodium hydroxide is added dropwise; a green precipitate forms which is insoluble in excess. 2. Dilute nitric acid is added followed by aqueous barium nitrate; a white precipitate forms.
What is the formula of the salt?
A.\(\text{CuSO}_4\)
B.\(\text{FeSO}_4\)
C.\(\text{FeCl}_2\)
D.\(\text{Fe}_2(\text{SO}_4)_3\)
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解题
The formation of a green precipitate with aqueous sodium hydroxide that is insoluble in excess confirms the presence of iron(II) ions, \(\text{Fe}^{2+}\). The formation of a white precipitate upon adding dilute nitric acid and aqueous barium nitrate confirms the presence of sulfate ions, \(\text{SO}_4^{2-}\). Therefore, the salt is iron(II) sulfate, \(\text{FeSO}_4\).
评分标准
B is correct [1]. Fe2+ gives a green precipitate insoluble in excess NaOH; SO4(2-) gives a white precipitate with acidified Ba(NO3)2.
题目 24 · 選擇題
1 分
A metal saucepan containing cold water is placed on an electric hotplate. Which row correctly identifies the principal method of thermal energy transfer through the metal base of the pan and through the bulk of the water?
A.Through the base of the pan: conduction | Through the water: convection
B.Through the base of the pan: conduction | Through the water: radiation
C.Through the base of the pan: convection | Through the water: conduction
D.Through the base of the pan: radiation | Through the water: convection
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解题
Thermal energy is transferred through the solid metal base of the saucepan primarily by conduction (via lattice vibrations and free electron diffusion). The thermal energy is transferred through the liquid water by convection, where heated less dense water rises and cooler denser water sinks to form convection currents.
评分标准
A is correct [1]. Conduction occurs through the solid metal base and convection through the liquid water.
题目 25 · 選擇題
1 分
Which statement correctly describes a reaction or property of ethane or ethene?
A.Ethane rapidly decolourises aqueous bromine at room temperature.
B.Ethene reacts with steam in the presence of a catalyst to produce ethanol.
C.Ethane and ethene are both unsaturated hydrocarbons.
D.The complete combustion of ethene produces carbon monoxide and hydrogen gas.
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解题
Ethene is an unsaturated alkene containing a carbon-carbon double bond (\(\text{C=C}\)). It reacts with steam in the presence of an acid catalyst to produce ethanol via an addition reaction. Ethane is a saturated alkane and does not decolourise bromine water rapidly at room temperature without UV light.
评分标准
B is correct [1]. Ethene undergoes addition with steam (hydration) to form ethanol.
题目 26 · 選擇題
1 分
An object of mass \(4.0\text{ kg}\) is travelling at an initial speed of \(5.0\text{ m/s}\). A constant resultant force of \(6.0\text{ N}\) acts on the object in the direction of its motion over a distance of \(8.0\text{ m}\).
What is the work done on the object by this force, and what was the initial kinetic energy of the object?
Work done is calculated as \(W = F \times d = 6.0\text{ N} \times 8.0\text{ m} = 48\text{ J}\). Initial kinetic energy is calculated as \(E_k = \frac{1}{2} m v^2 = \frac{1}{2} \times 4.0\text{ kg} \times (5.0\text{ m/s})^2 = 0.5 \times 4.0 \times 25 = 50\text{ J}\).
评分标准
C is correct [1]. Work done = 48 J and Initial kinetic energy = 50 J.
题目 27 · 選擇題
1 分
Strips of potato tissue of equal initial length were placed in four sucrose solutions of different concentrations, \(W\), \(X\), \(Y\) and \(Z\).
After 60 minutes, the changes in length of the potato strips were measured: - solution \(W\): \(+1.8\text{ mm}\) - solution \(X\): \(-2.4\text{ mm}\) - solution \(Y\): \(0.0\text{ mm}\) - solution \(Z\): \(-0.9\text{ mm}\)
Which sequence ranks the sucrose concentrations of the solutions from lowest to highest?
A.\(W \rightarrow Y \rightarrow Z \rightarrow X\)
B.\(X \rightarrow Z \rightarrow Y \rightarrow W\)
C.\(W \rightarrow X \rightarrow Z \rightarrow Y\)
D.\(Y \rightarrow W \rightarrow Z \rightarrow X\)
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解题
Water moves by osmosis from a region of higher water potential (lower solute/sucrose concentration) to a region of lower water potential (higher solute/sucrose concentration).
1. In solution \(W\), the strip gained length (\(+1.8\text{ mm}\)), showing water entered the cells. Solution \(W\) has the highest water potential and therefore the lowest sucrose concentration. 2. In solution \(Y\), there was no change in length (\(0.0\text{ mm}\)), indicating no net movement of water. 3. In solutions \(Z\) and \(X\), water left the cells causing the strips to decrease in length. Solution \(X\) caused a larger decrease (\(-2.4\text{ mm}\)) than solution \(Z\) (\(-0.9\text{ mm}\)), meaning \(X\) has a higher sucrose concentration than \(Z\).
Therefore, the order of sucrose concentration from lowest to highest is \(W \rightarrow Y \rightarrow Z \rightarrow X\).
评分标准
A ; [1]
题目 28 · 選擇題
1 分
A student carries out two qualitative tests on separate samples of an aqueous solution of salt \(Q\).
1. Dilute nitric acid is added followed by aqueous barium nitrate: a white precipitate forms. 2. Aqueous sodium hydroxide is added dropwise and then in excess: a white precipitate forms that dissolves in excess to give a colourless solution.
Which compound is salt \(Q\)?
A.aluminium sulfate
B.calcium chloride
C.copper(II) sulfate
D.zinc chloride
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解题
1. The formation of a white precipitate with aqueous barium nitrate in the presence of dilute nitric acid confirms the presence of sulfate ions (\(\text{SO}_4^{2-}\)). 2. The formation of a white precipitate with aqueous sodium hydroxide that dissolves in excess to give a colourless solution indicates either aluminium ions (\(\text{Al}^{3+}\)) or zinc ions (\(\text{Zn}^{2+}\)).
Combining these two observations, salt \(Q\) must be aluminium sulfate (\(\text{Al}_2(\text{SO}_4)_3\)).
评分标准
A ; [1]
题目 29 · 選擇題
1 分
Chlorine water is added to separate aqueous solutions of potassium bromide and potassium iodide.
Which row correctly describes the observations for both mixtures?
Chlorine is more reactive than both bromine and iodine. - Chlorine displaces bromide ions from potassium bromide to form aqueous bromine (\(\text{Br}_2\)), which turns the solution orange-brown: $$\text{Cl}_2\text{(aq)} + 2\text{KBr(aq)} \rightarrow 2\text{KCl(aq)} + \text{Br}_2\text{(aq)}$$ - Chlorine displaces iodide ions from potassium iodide to form aqueous iodine (\(\text{I}_2\)), which turns the solution brown: $$\text{Cl}_2\text{(aq)} + 2\text{KI(aq)} \rightarrow 2\text{KCl(aq)} + \text{I}_2\text{(aq)}$$
Hence, row A is correct.
评分标准
A ; [1]
题目 30 · 選擇題
1 分
An electric scooter travels along a straight, horizontal path.
- It accelerates uniformly from rest to a speed of \(6.0\text{ m/s}\) in \(4.0\text{ s}\). - It then travels at a constant speed of \(6.0\text{ m/s}\) for \(8.0\text{ s}\). - Finally, it decelerates uniformly to rest in \(3.0\text{ s}\).
What is the total distance travelled by the scooter?
A.\(45\text{ m}\)
B.\(60\text{ m}\)
C.\(69\text{ m}\)
D.\(90\text{ m}\)
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解题
The total distance travelled is equal to the area under the speed-time graph:
Four identical metal containers are filled with equal volumes of boiling water at \(100^\circ\text{C}\). Each container has a different exterior surface finish: - Container 1: dull black - Container 2: shiny silver - Container 3: dull white - Container 4: shiny black
Which container cools down at the fastest rate, and which thermal transfer process is mainly responsible for the difference in cooling rates?
A.Container 1, due to thermal radiation
B.Container 1, due to thermal conduction
C.Container 2, due to thermal radiation
D.Container 2, due to thermal convection
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解题
Dull, black surfaces are the best emitters of thermal (infrared) radiation, whereas shiny surfaces are poor emitters.
Since all containers have identical geometry, contents, and initial temperature, the rate of heat loss by conduction and convection to the surrounding air is essentially the same. The difference in cooling rates is due to the difference in the rate of thermal radiation emitted.
Therefore, Container 1 (dull black) emits radiation at the highest rate and cools the fastest.
评分标准
A ; [1]
题目 32 · 選擇題
1 分
A student carries out chemical tests on an unknown aqueous solution \(\text{X}\).
1. Adding aqueous sodium hydroxide produces a green precipitate that remains insoluble in excess sodium hydroxide. 2. Adding dilute nitric acid followed by aqueous barium nitrate produces a white precipitate.
Which compound is present in solution \(\text{X}\)?
A.iron(II) sulfate
B.iron(II) chloride
C.iron(III) sulfate
D.iron(III) chloride
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解题
Aqueous sodium hydroxide forming a green precipitate insoluble in excess confirms the presence of iron(II) ions, \(\text{Fe}^{2+}\). Adding dilute nitric acid followed by aqueous barium nitrate produces a white precipitate of barium sulfate, confirming the presence of sulfate ions, \(\text{SO}_4^{2-}\). Therefore, the compound is iron(II) sulfate.
评分标准
A [1]
题目 33 · 選擇題
1 分
Four identical metal containers contain the same volume of hot water at \(80\ ^\circ\text{C}\). The outer surfaces of the containers have different colours and textures.
Which container cools down to room temperature at the fastest rate?
A.black and dull
B.black and shiny
C.white and dull
D.white and shiny
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解题
Dull, dark (black) surfaces are the best emitters of thermal (infrared) radiation. Shiny and light-coloured (white) surfaces are poor emitters. Therefore, the container that is dull black will emit thermal radiation most rapidly and cool down at the fastest rate.
评分标准
A [1]
题目 34 · 選擇題
1 分
An electric trolley of mass \(12\text{ kg}\) accelerates uniformly from rest to a speed of \(4.0\text{ m/s}\) in a time of \(6.0\text{ s}\).
What is the resultant force acting on the trolley?
Which statement correctly describes a difference between ethane and ethene?
A.Ethane decolourises aqueous bromine, but ethene does not.
B.Ethane contains only single covalent bonds, whereas ethene contains a carbon-carbon double bond.
C.Ethane produces carbon dioxide and water on complete combustion, but ethene does not.
D.Ethane is an unsaturated hydrocarbon, whereas ethene is a saturated hydrocarbon.
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解题
Ethane is an alkane containing only single covalent bonds (saturated hydrocarbon). Ethene is an alkene containing a carbon-carbon double bond (unsaturated hydrocarbon). Ethene decolourises aqueous bromine, not ethane, and both undergo complete combustion to produce carbon dioxide and water.
评分标准
B [1]
题目 36 · 選擇題
1 分
Cylinders of potato tissue of equal initial mass are immersed in sucrose solutions of different concentrations: \(0.0\text{ mol/dm}^3\), \(0.2\text{ mol/dm}^3\), \(0.4\text{ mol/dm}^3\), and \(0.8\text{ mol/dm}^3\).
After \(60\) minutes, the potato cylinder placed in the \(0.8\text{ mol/dm}^3\) sucrose solution has decreased in mass.
Which statement explains this result?
A.Sucrose molecules moved into the plant cells by diffusion.
B.Sucrose molecules moved out of the plant cells by active transport.
C.Water molecules moved into the plant cells down a water potential gradient.
D.Water molecules moved out of the plant cells down a water potential gradient.
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解题
A \(0.8\text{ mol/dm}^3\) sucrose solution has a lower water potential (higher solute concentration) than the potato cell sap. Consequently, water moves out of the plant cells by osmosis down the water potential gradient, resulting in a net decrease in tissue mass.
A domestic solar collector is installed on the roof of a house to heat water.
(a) The solar collector has a metal backplate painted matt black and is covered with a transparent glass sheet.
(i) State the main process by which thermal energy from the Sun reaches the collector. [1]
(ii) Explain why the metal backplate is painted matt black rather than left shiny silver. [2]
(b) Water with a mass of \(45\text{ kg}\) enters the collector at an initial temperature of \(18\,^\circ\text{C}\) and leaves at a temperature of \(54\,^\circ\text{C}\).
The specific heat capacity of water is \(4200\text{ J}/(\text{kg}\,^\circ\text{C})\).
Calculate the thermal energy transferred to the water. Show your working and state the unit. [3]
(c) Explain, in terms of particles, how thermal energy is transferred through the solid copper pipes inside the collector. [3]
[Total: 9]
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解题
(a)(i) Radiation (or infrared radiation).
(a)(ii) Matt black surfaces are good/better absorbers of infrared radiation / thermal energy (1 mark), so more heat is absorbed compared to shiny silver surfaces which reflect radiation (1 mark).
(b) Temperature change \(\Delta T = 54\,^\circ\text{C} - 18\,^\circ\text{C} = 36\,^\circ\text{C}\). \(\text{Energy } E = m c \Delta T = 45 \times 4200 \times 36\) \(E = 6\,804\,000\text{ J}\) (or \(6.804\text{ MJ}\)).
(c) Particles (atoms/ions) at the heated end gain kinetic energy and vibrate more vigorously (1 mark); these vibrations are passed on to adjacent particles by collisions (1 mark); free / delocalised electrons also move rapidly through the metal lattice transferring energy throughout the copper (1 mark).
评分标准
(a)(i) radiation / infra-red radiation [1] (a)(ii) (matt black is a) good / best absorber of radiation / heat; [1] shiny surfaces reflect (more) radiation / are poor absorbers; [1] (b) (temperature change =) \(36\,^\circ\text{C}\); [1] \(E = 45 \times 4200 \times 36\) / substitution into \(E = mc\Delta T\); [1] \(6\,804\,000\text{ J}\) / \(6.804\text{ MJ}\) (correct value and unit); [1] (c) particles / ions vibrate more (as temperature rises); [1] vibrations passed from particle to particle / collisions between adjacent particles; [1] delocalised / free electrons move through the lattice (transferring energy); [1]
题目 2 · Structured
8.88 分
Hydrocarbons are organic compounds containing carbon and hydrogen only.
(a) Dodecane, \(\text{C}_{12}\text{H}_{26}\), is an alkane present in kerosene. It can be cracked industrially to produce octane, \(\text{C}_8\text{H}_{18}\), and an alkene.
(i) State two industrial conditions required for cracking. [2]
(ii) Complete the chemical equation for the cracking of dodecane: \[\text{C}_{12}\text{H}_{26} \rightarrow \text{C}_8\text{H}_{18} + 2\,\text{..........}\] [1]
(b) Describe a chemical test to distinguish between octane (an alkane) and ethene (an alkene). State the reagent used and the observation for each compound.
observation with octane: ....................................................
observation with ethene: .................................................... [3]
(c) Ethene undergoes complete combustion in excess oxygen to form carbon dioxide and water.
Write the balanced chemical equation for the complete combustion of ethene, \(\text{C}_2\text{H}_4\). [2]
[Total: 8]
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解题
(a)(i) High temperature (450 °C to 750 °C) and a catalyst (aluminium oxide / silicon dioxide / zeolite).
(a)(ii) \(\text{C}_{12}\text{H}_{26} \rightarrow \text{C}_8\text{H}_{18} + 2\,\text{C}_2\text{H}_4\). The missing formula is \(\text{C}_2\text{H}_4\).
(b) Reagent: aqueous bromine / bromine water. Observation with octane: remains orange / brown / yellow (no change). Observation with ethene: orange / brown to colourless (decolourises).
(c) Red blood cells transport oxygen from the lungs to respiring tissues.
Describe two structural adaptations of a red blood cell and explain how each adaptation helps it to carry out its function. [4]
(d) Name the blood vessel that transports oxygenated blood from the lungs directly to the left atrium of the heart. [1]
[Total: 9]
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解题
(a) Blood passes through the heart twice for every one complete circuit of the body (one circuit to the lungs/pulmonary circuit and one circuit to the rest of the body/systemic circuit).
(b) Thickness of muscular wall: Artery is thick, Vein is thin. Presence of valves: Artery has no valves (along length), Vein has valves.
(c) Adaptation 1: Biconcave disc shape / large surface area to volume ratio (1 mark), which allows rapid diffusion of oxygen into and out of the cell (1 mark). Adaptation 2: Contains haemoglobin / lack of nucleus (1 mark), which binds with oxygen to form oxyhaemoglobin / allows more room to carry haemoglobin (1 mark).
(d) Pulmonary vein.
评分标准
(a) blood passes through the heart twice; [1] for one complete circuit (of the body) / (one circuit to lungs and one to body); [1] (b) Artery: thick (wall) AND Vein: thin (wall); [1] Artery: no valves / absent AND Vein: valves present; [1] (c) biconcave disc shape / large surface area to volume ratio; [1] increases rate of diffusion of oxygen; [1] contains haemoglobin / lacks a nucleus; [1] haemoglobin binds to oxygen / lack of nucleus allows more space for haemoglobin; [1] (d) pulmonary vein; [1]
题目 4 · Structured
8.88 分
A student carries out tests to identify the ions present in an unknown solid sample, **W**.
(a) Solid **W** is dissolved in distilled water to make solution **W**.
(i) Describe a chemical test to show that solution **W** contains iron(II) ions, \(\text{Fe}^{2+}\).
(a)(ii) Test: Acidify with dilute nitric acid (or dilute hydrochloric acid) (1 mark), then add aqueous barium nitrate (or aqueous barium chloride) (1 mark). Observation: White precipitate formed (1 mark).
(b)(i) Pencil lead (graphite) is insoluble in the solvent, so it will not dissolve, spread, or interfere with the results.
(b)(ii) \(R_f = \frac{\text{distance moved by substance}}{\text{distance moved by solvent front}} = \frac{3.6\text{ cm}}{6.0\text{ cm}} = 0.60\).
评分标准
(a)(i) add aqueous sodium hydroxide / aqueous ammonia; [1] green precipitate; [1] (a)(ii) add dilute nitric acid / dilute hydrochloric acid; [1] add (aqueous) barium nitrate / barium chloride; [1] white precipitate; [1] (b)(i) pencil is insoluble / ink would dissolve / run / separate and interfere with spots; [1] (b)(ii) \(\frac{3.6}{6.0}\); [1] \(0.60\) / \(0.6\); [1]
题目 5 · Structured
8.88 分
An electric scooter and its rider have a total mass of \(90\text{ kg}\). The scooter accelerates along a straight, horizontal track from rest to a final speed of \(8.0\text{ m/s}\) in a time of \(5.0\text{ s}\).
(d) Principle of conservation of energy: Energy cannot be created or destroyed, only transferred from one form/store to another (1 mark). Energy transfer: Kinetic energy of the scooter is transferred to thermal/heat energy in the brake pads/surroundings (1 mark).
评分标准
(a) \(a = \frac{\Delta v}{t}\) / \(\frac{8.0}{5.0}\); [1] \(1.6\) (\(\text{m/s}^2\)); [1] (b) \(F = ma\) / \(90 \times 1.6\); [1] \(144\) (\(\text{N}\)); [1] (c) \(E_k = \frac{1}{2}mv^2\) / \(0.5 \times 90 \times 8.0^2\); [1] \(2880\) (\(\text{J}\)) / \(2.88\text{ kJ}\); [1] (d) energy cannot be created or destroyed (only transferred from one store to another); [1] kinetic energy (of scooter) is transferred to thermal energy / heat (in the brakes / surroundings); [1]
题目 6 · Structured
8.88 分
(a) Define the term osmosis. [2]
(b) A student investigates the effect of sucrose concentration on potato tissue. Potato cylinders of equal length (50.0 mm) and mass are placed into test-tubes containing different concentrations of sucrose solution for 2 hours.
(i) The potato cylinder in 0.0 mol/dm3 sucrose solution (pure water) increases in mass. Explain why this increase in mass occurs. [3]
(ii) State two variables that the student must keep constant in this investigation to ensure valid results. [2]
(c) Name the structure in a plant cell that prevents it from bursting when placed in pure water. [1]
(d) State the term used to describe a plant cell when its cytoplasm shrinks away from the cell wall due to water loss. [1]
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解题
(a) Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane. (b)(i) Pure water has a higher water potential than the potato cell cytoplasm/vacuole. Water molecules move down the water potential gradient into the potato cells by osmosis, causing an increase in cell mass/volume. (b)(ii) Any two from: temperature of the solutions, volume of sucrose solution, initial surface area/diameter of the cylinders, duration of immersion, source/variety of potato. (c) Cell wall (made of cellulose). (d) Plasmolysed (plasmolysis).
评分标准
(a) Net movement of water (molecules) [1]; from higher to lower water potential / down a water potential gradient through a partially permeable membrane [1]. (b)(i) Water potential of solution is higher than inside potato cells / potato sap [1]; water enters (cells) by osmosis [1]; down a water potential gradient [1]. (b)(ii) Any two from: temperature / volume of solution / diameter or surface area of cylinder / time left in solution [2]. (c) Cell wall [1]. (d) Plasmolysed / plasmolysis [1].
题目 7 · Structured
8.88 分
(a) Petroleum (crude oil) is a mixture of hydrocarbons that is separated by fractional distillation.
(i) State the physical property that enables the components of petroleum to be separated by fractional distillation. [1]
(ii) State one major use of each of the following petroleum fractions: - refinery gas fraction - bitumen fraction [2]
(b) Long-chain hydrocarbons undergo catalytic cracking to produce smaller, more useful molecules.
(i) State two reaction conditions required for industrial catalytic cracking. [2]
(ii) Decane (\(\text{C}_{10}\text{H}_{22}\)) is cracked to produce ethene (\(\text{C}_2\text{H}_4\)) and one other product. Complete the chemical equation for this reaction:
(c) Describe a chemical test to distinguish between an alkane and an alkene. Include the result for each type of hydrocarbon. [3]
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解题
(a)(i) Difference in boiling points (or condensation temperatures). (a)(ii) Refinery gas: fuel for heating/cooking (or bottled gas); Bitumen: making roads / road surfacing / roofing. (b)(i) High temperature (approx. 450–700 °C) and a catalyst (aluminium oxide / silicon dioxide / zeolite). (b)(ii) Total carbons = 10, total hydrogens = 22. Subtracting \(\text{C}_2\text{H}_4\) gives \(\text{C}_8\text{H}_{18}\). (c) Reagent: aqueous bromine / bromine water. With alkane: stays orange / brown / yellow (no change). With alkene: turns colourless / decolourises.
评分标准
(a)(i) Boiling point / condensation point [1]. (a)(ii) Refinery gas: (bottled) gas for heating / cooking / camping gas [1]; Bitumen: surfacing roads / making asphalt / roofing [1]. (b)(i) High temperature / 450–750 °C [1]; catalyst / zeolite / aluminium oxide / silica [1]. (b)(ii) \(\text{C}_8\text{H}_{18}\) [1]. (c) Add bromine water / aqueous bromine [1]; alkane: remains orange / brown / no reaction [1]; alkene: decolourises / turns colourless [1].
题目 8 · Structured
8.88 分
(a) A solar thermal panel absorbs radiation from the Sun to heat water. The panel consists of metal pipes mounted on a black metal backplate beneath a glass cover.
(i) Explain why the metal pipes are made of copper rather than plastic. [2]
(ii) Explain why the backplate is painted matte black. [2]
(b) Describe how thermal energy is transferred through the water within the storage tank by convection. [3]
(c) The water storage tank contains \(45\text{ kg}\) of water. The specific heat capacity of water is \(4200\text{ J}/(\text{kg}\cdot^\circ\text{C})\). Calculate the thermal energy needed to raise the temperature of the water from \(18^\circ\text{C}\) to \(58^\circ\text{C}\). [2]
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解题
(a)(i) Copper is a good conductor of heat/thermal energy, allowing rapid transfer of heat from the panel surface to the water inside. (a)(ii) Dark matte black surfaces are good absorbers (poor reflectors) of infrared / thermal radiation. (b) Water at the heated section gains thermal energy, expands and becomes less dense. The less dense warm water rises. Cooler, denser water sinks to take its place, setting up a continuous convection current. (c) Use the equation: \(E = mc\Delta T\) \(\Delta T = 58^\circ\text{C} - 18^\circ\text{C} = 40^\circ\text{C}\) \(E = 45\text{ kg} \times 4200\text{ J}/(\text{kg}\cdot^\circ\text{C}) \times 40^\circ\text{C} = 7\,560\,000\text{ J}\) (or \(7.56\text{ MJ}\) or \(7560\text{ kJ}\)).
评分标准
(a)(i) Copper is a good (thermal) conductor [1]; plastic is an insulator / poor conductor ORA [1]. (a)(ii) Black / matte is a good / the best absorber of (thermal / infrared) radiation [1]; reduces reflection of radiation [1]. (b) Heated water expands [1]; density of heated water decreases / it becomes less dense [1]; warm water rises and cold / denser water sinks (forming a convection current) [1]. (c) Temperature difference \(\Delta T = 40\ (^∘\text{C})\) and correct substitution \(45 \times 4200 \times 40\) [1]; \(7\,560\,000\text{ J}\) / \(7.56 \times 10^6\text{ J}\) / \(7560\text{ kJ}\) [1].
题目 9 · Structured
8.88 分
(a) A student is provided with a solution of an unknown inorganic salt, compound **Q**. Compound **Q** contains one cation and one anion.
(i) Addition of aqueous sodium hydroxide to a sample of solution **Q** produces a green precipitate that is insoluble in excess sodium hydroxide. Identify the cation present in compound **Q**. [1]
(ii) Addition of dilute nitric acid followed by aqueous silver nitrate to another sample of solution **Q** produces a cream precipitate. Identify the anion present in compound **Q**. [1]
(iii) Deduce the chemical formula of compound **Q**. [1]
(b) The student also performs paper chromatography to analyse the dyes present in a sample of food colouring.
(i) State why the baseline is drawn in pencil rather than pen ink. [1]
(ii) Describe how the level of the solvent must be positioned relative to the baseline at the beginning of the experiment. [1]
(iii) A blue dye spot travels a distance of \(36\text{ mm}\) from the baseline. The solvent front travels a distance of \(60\text{ mm}\) from the baseline. Calculate the \(R_f\) value of the blue dye. [2]
(c) State the test and the positive result for chlorine gas. [2]
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解题
(a)(i) The green precipitate with sodium hydroxide indicates the iron(II) ion, \(\text{Fe}^{2+}\). (a)(ii) The cream precipitate with nitric acid and silver nitrate indicates the bromide ion, \(\text{Br}^-\). (a)(iii) Combining \(\text{Fe}^{2+}\) and \(\text{Br}^-\) gives \(\text{FeBr}_2\). (b)(i) Pencil graphite is insoluble in the solvent and therefore will not separate or interfere with the chromatogram. (b)(ii) The solvent level must be below the baseline so the spots do not dissolve directly into the solvent reservoir. (b)(iii) \(R_f = \frac{\text{distance moved by substance}}{\text{distance moved by solvent front}} = \frac{36\text{ mm}}{60\text{ mm}} = 0.60\). (c) Test: damp litmus paper (or damp universal indicator paper). Result: bleaches white (or turns red then white).
评分标准
(a)(i) Iron(II) / \(\text{Fe}^{2+}\) [1]. (a)(ii) Bromide / \(\text{Br}^-\) [1]. (a)(iii) \(\text{FeBr}_2\) [1] (ecf from (a)(i) and (a)(ii)). (b)(i) Pencil is insoluble / ink would dissolve / ink would separate / interfere with results [1]. (b)(ii) Below the baseline / below the spot [1]. (b)(iii) Correct formula / working \(\frac{36}{60}\) [1]; \(0.60\) or \(0.6\) [1]. (c) (Damp) litmus paper / universal indicator paper [1]; bleaches / turns white [1].
Paper 63 (Alternative to Practical)
Answer all questions in the spaces provided.
4 题目 · 40 分
题目 1 · Practical/Investigation
10 分
1 A student investigates the effect of different concentrations of sucrose solution on cylinders of turnip tissue.
(a) The student cuts five turnip cylinders of equal length and measures the initial mass of each cylinder using an electronic balance.
(i) Fig. 1.1 shows the balance reading for the initial mass of the turnip cylinder placed in 0.4 mol / dm^3 sucrose solution.
[Balance display: 3.48 g]
Record this mass in Table 1.1. [1]
Table 1.1 | Concentration of sucrose solution / (mol / dm^3) | Initial mass / g | Final mass / g | Change in mass / g | Percentage change in mass / % | | :--- | :--- | :--- | :--- | :--- | | 0.0 | 3.50 | 3.99 | +0.49 | +14.0 | | 0.2 | 3.45 | 3.69 | +0.24 | +7.0 | | 0.4 | ...... | 3.48 | 0.00 | 0.0 | | 0.6 | 3.52 | 3.27 | -0.25 | ...... | | 0.8 | 3.48 | 3.01 | -0.47 | -13.5 |
(ii) Calculate the percentage change in mass for the turnip cylinder in 0.6 mol / dm^3 sucrose solution.
Use the equation: $$\text{percentage change} = \frac{\text{change in mass}}{\text{initial mass}} \times 100$$
Give your answer to one decimal place. Include the appropriate sign (+ or -).
(b) (i) Describe how the percentage change in mass varies as the concentration of sucrose solution increases from 0.0 mol / dm^3 to 0.8 mol / dm^3. [2]
(ii) Use Table 1.1 to estimate the concentration of sucrose solution that has the same water potential as the turnip tissue. Explain your answer. [2]
(c) (i) Before measuring the final mass, the student dries the surface of each cylinder with a paper towel. Explain why this step is necessary. [1]
(ii) State two variables that should be controlled in this investigation to ensure a valid comparison. [2]
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解题
(a)(i) Reading from balance display: 3.48 g. (a)(ii) Change in mass = -0.25 g. Initial mass = 3.52 g. $$\text{Percentage change} = \frac{-0.25}{3.52} \times 100 = -7.102... \approx -7.1\%$$ (b)(i) As the concentration increases from 0.0 to 0.8 mol / dm^3, the percentage change in mass decreases continuously from +14.0% to -13.5%. (b)(ii) Concentration = 0.4 mol / dm^3. At this concentration, change in mass is 0.00 g / percentage change is 0.0%, indicating no net movement of water. (c)(i) Excess surface liquid would contribute to the recorded mass, resulting in an inaccurate final mass measurement. (c)(ii) Any two controlled variables: temperature, immersion time, volume of sucrose solution, diameter/source of turnip cylinders.
评分标准
(a)(i) 3.48 ; [1] (a)(ii) -7.1 (%);; [2] [Allow 1 mark for correct numerical value without sign / incorrect rounding: e.g. 7.1 or -7.10] [Allow 1 mark for correct working: (-0.25 / 3.52) * 100] (b)(i) as sucrose concentration increases, percentage change decreases / mass change goes from positive to negative / mass decreases ; [1] credited comparative data quote or linear relationship specified ; [1] (b)(ii) 0.4 (mol / dm^3) ; [1] (because) no change in mass / 0.0% change / no net movement of water ; [1] (c)(i) to remove surface liquid / avoid weighing liquid on the outside of the cylinder ; [1] (c)(ii) any two from: - temperature of the solution ; - time / duration cylinders left in solution ; - volume of solution ; - surface area / diameter / length / type of turnip ;; [Max 2]
题目 2 · Practical/Investigation
10 分
2 A student carries out tests to identify the ions present in solid compound J and aqueous solution K.
(a) Tests on solid compound J:
• Test 1: Solid J is heated in a dry test-tube. A colorless gas is evolved that turns damp red litmus paper blue.
(i) Name the gas evolved in Test 1. [1]
(ii) Identify the cation present in solid J based on Test 1. [1]
• Test 2: Solid J is dissolved in distilled water to make solution J. Dilute nitric acid is added, followed by aqueous silver nitrate. A cream/off-white precipitate forms.
(iii) Identify the anion present in solid J based on Test 2. [1]
(iv) State the chemical formula of solid J. [1]
(b) Tests on aqueous solution K:
• Test 3: Aqueous sodium hydroxide is added dropwise and then in excess to solution K. A light blue precipitate forms, which is insoluble in excess.
(i) Identify the cation present in solution K. [1]
• Test 4: Dilute hydrochloric acid is added to a sample of solution K, followed by aqueous barium chloride. A white precipitate forms.
(ii) Identify the anion present in solution K. [1]
(c) The student wants to obtain pure, dry crystals of the dissolved salt from solution K.
(i) Describe the procedure the student should follow to prepare dry crystals from solution K. [3]
(ii) State one safety precaution the student should take during the crystallization process and give a reason for this precaution. [1]
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解题
(a)(i) The gas that turns damp red litmus blue is ammonia (NH3). (a)(ii) Ammonium (NH4+) produces ammonia gas when thermal decomposition or base reaction occurs. (a)(iii) Silver nitrate with nitric acid producing a cream/off-white precipitate indicates bromide ions (Br-). (a)(iv) Ammonium bromide is NH4Br. (b)(i) Aqueous sodium hydroxide giving a light blue precipitate insoluble in excess confirms copper(II) ions (Cu2+). (b)(ii) Barium chloride with dilute hydrochloric acid producing a white precipitate confirms sulfate ions (SO4^2-). (c)(i) Heat the solution to evaporate water until the crystallization point / saturation point is reached. Allow the hot saturated solution to cool so crystals form. Filter the mixture to collect the crystals, then dry them between sheets of filter paper or in a desiccator / low-temperature oven. (c)(ii) Wear eye protection / safety glasses to prevent eye damage from boiling liquid spitting.
评分标准
(a)(i) ammonia / NH3 ; [1] (a)(ii) ammonium / NH4+ ; [1] (a)(iii) bromide / Br- ; [1] (a)(iv) NH4Br ; [1] (b)(i) copper(II) / Cu2+ (reject copper / Cu) ; [1] (b)(ii) sulfate / SO4^2- ; [1] (c)(i) heat / evaporate (until crystallization point / saturation point / crystals form on glass rod) ; [1] leave to cool (and crystallize) ; [1] filter AND dry (between filter papers / warm oven / desiccator) ; [1] (c)(ii) wear safety glasses / eye protection because hot liquid may spit / splash (OR use tongs to hold hot evaporating basin to avoid burns) ; [1]
题目 3 · Practical/Investigation
10 分
4 A student is provided with constantan resistance wires of different lengths and wants to investigate how the electrical resistance of a wire depends on its length.
(a) Fig. 4.1 shows an ammeter and a voltmeter used in a preliminary test.
potential difference V = ......................... V [1]
(ii) Calculate the resistance R of the wire.
Use the equation: $$R = \frac{V}{I}$$
Give your answer to two significant figures.
resistance R = ......................... \(\Omega\) [2]
(b) Plan an investigation to determine the relationship between the length of a resistance wire and its electrical resistance.
You are provided with: • a power supply (d.c.) • a switch • connecting leads and crocodile clips • a metre rule • constantan wire of length 100 cm • an ammeter and a voltmeter
In your plan, you should include: • a circuit diagram of the apparatus you will use • a brief description of the method, including how you will vary the length • the measurements you will take and the variables you will control • a table with headings to record your measurements (you do not need to include data) • how you will use your results to reach a conclusion. [7]
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解题
(a)(i) Current I = 0.36 A; Potential difference V = 2.7 V. (a)(ii) $$R = \frac{2.7}{0.36} = 7.5\text{ }\Omega$$ (b) Plan: 1. Circuit diagram: series circuit containing power supply, switch, ammeter, and resistance wire; voltmeter connected in parallel across the wire. 2. Method: Attach crocodile clips to the wire at a measured initial length (e.g. 20 cm). Close the switch briefly, record current I and potential difference V, and open the switch. Repeat for at least 5 different lengths (e.g. 20, 40, 60, 80, 100 cm). 3. Variables: Independent variable = length of wire; Dependent variable = current and voltage (to calculate resistance); Controlled variables = wire material (constantan), cross-sectional area/diameter/gauge of wire, temperature (keep current low / open switch between readings). 4. Results table with appropriate headings and units: Length / cm, Potential difference / V, Current / A, Resistance / \(\Omega\). 5. Analysis: Calculate \(R = V / I\) for each length. Plot a graph of Resistance (y-axis) against Length (x-axis). If the line is straight and passes through the origin, resistance is directly proportional to length.
评分标准
(a)(i) I = 0.36 (A) AND V = 2.7 (V) ; [1] (a)(ii) 7.5 (\(\Omega\)) ; [2] [Allow 1 mark for correct substitution: 2.7 / 0.36] (b) 7 marks allocated from the following points: 1. Circuit diagram: power supply, switch, ammeter in series with wire AND voltmeter in parallel across test wire (standard symbols) ; [1] 2. Method: connect crocodile clips to change length of wire AND measure length with metre rule ; [1] 3. Range: test at least five different lengths (e.g. 20, 40, 60, 80, 100 cm) ; [1] 4. Key controlled variables: same diameter/thickness of wire / switch off between readings to keep temperature constant ; [1] 5. Measurements: record current (I) from ammeter and potential difference (V) from voltmeter ; [1] 6. Table: drawn with columns for length (with unit cm/m), current (A), potential difference (V), and resistance (\(\Omega\)) ; [1] 7. Processing / Conclusion: calculate \(R = V / I\) AND plot graph of resistance against length (or state that straight line through origin shows direct proportionality) ; [1]
题目 4 · Practical/Investigation
10 分
A student investigates the change in mass of potato cylinders placed in different concentrations of sucrose solution.
(a) The student cuts five potato cylinders of equal initial length and mass. (i) State the piece of apparatus the student uses to measure the mass of each cylinder accurately to two decimal places. [1] (ii) State one variable the student keeps constant when preparing the potato cylinders. [1]
(b) The potato cylinders are placed in five boiling tubes containing sucrose solutions of concentrations \(0.0\text{ mol/dm}^3\), \(0.2\text{ mol/dm}^3\), \(0.4\text{ mol/dm}^3\), \(0.6\text{ mol/dm}^3\), and \(0.8\text{ mol/dm}^3\). After \(45\text{ minutes}\), the cylinders are removed, gently blotted with a paper towel, and re-weighed. Table 1.1 shows the initial and final mass for each cylinder.
Calculate the percentage change in mass for the potato cylinder placed in \(0.6\text{ mol/dm}^3\) sucrose solution. Record your value to one decimal place in the space in Table 1.1. [2]
(c) (i) Plot a graph of percentage change in mass (vertical axis) against concentration of sucrose solution (horizontal axis). [3] (ii) Draw the line of best fit through your points. [1]
(d) Use your graph to determine the concentration of sucrose solution at which there is no net movement of water into or out of the potato tissue. State the value. [1]
(e) Explain why it is important to blot the potato cylinders with a paper towel before re-weighing them. [1]
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解题
(a) (i) An electronic balance or digital balance is used to measure mass to two decimal places. (ii) Variables kept constant during preparation include the diameter (cross-sectional area) of the cylinder, initial length, or the variety/source of the potato.
(c) (i) Axes labelled with quantity and unit: percentage change in mass / \(\%\) on vertical axis, concentration of sucrose solution / \(\text{mol/dm}^3\) on horizontal axis. Sensible linear scale occupying more than half the grid. Points plotted accurately to within half a small square. (ii) A smooth line or curve of best fit drawn cleanly through the points.
(d) The sucrose concentration where no net movement occurs corresponds to \(y = 0\%\) change in mass, which is \(0.40\text{ mol/dm}^3\) (or candidate's intercept).
(e) Blotting removes liquid adhering to the surface of the cylinder that would otherwise add excess weight and cause an inaccurate, falsely high final mass.
评分标准
(a)(i) (electronic / digital) balance / top-pan balance [1] (a)(ii) diameter / thickness / cross-sectional area / variety of potato / volume of cylinder [1] (b) \(\frac{-0.23}{3.30} \times 100\) [1]; -7.0(\%) (must include negative sign, 1 d.p.) [1] (c)(i) Axes labelled with units: 'percentage change in mass / %' vs 'concentration of sucrose solution / mol/dm^3' [1]; Sensible linear scale using \(\ge 50\%\) of grid in both directions [1]; All 5 points plotted correctly to within \(\pm\) half a small square [1] (c)(ii) Well-drawn single line of best fit (straight line or smooth continuous curve) [1] (d) \(0.40\text{ mol/dm}^3\) / reading from candidate's graph where percentage change is zero \(\pm 0.02\) [1] (e) To remove excess surface liquid / water so only the internal mass of the tissue is measured [1]
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