2024 Cambridge IGCSE Chemistry (0620) Practice Paper with Answers

In a gas, the particles are widely spaced, randomly arranged, and free to move rapidly in all directions. Option A describes a solid, option B describes a liquid, and option D is scientifically incorrect as gas particles are not arranged in a regular pattern and are not stationary.

1 mark for correct choice C.

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Because they have the same number of protons, they also have the same number of electrons and identical chemical properties.

1 mark for correct choice B.

Element Y has 2 outer-shell electrons and needs to lose them to form a stable \(Y^{2+}\) ion. Element Z has 7 outer-shell electrons and needs to gain 1 electron to form a stable \(Z^-\) ion. Therefore, one atom of Y loses two electrons, and two atoms of Z each gain one electron to form the ionic compound \(YZ_2\).

1 mark for correct choice B.

A decrease in temperature indicates that heat energy is absorbed from the surroundings. This is the definition of an endothermic reaction.

1 mark for correct choice A.

Carbonates react with acids to produce salt, water, and carbon dioxide gas. Copper is unreactive with dilute acids; magnesium reacts to produce hydrogen gas; sodium hydroxide reacts in a neutralisation reaction to produce salt and water (no gas).

1 mark for correct choice C.

Metal Y is the least reactive as it does not react. Metal Z is more reactive than Y because it reacts slowly. Metal X is the most reactive because it fizzes very rapidly. Therefore, the order of reactivity from least to most reactive is Y, Z, X.

1 mark for correct choice B.

Fermentation of glucose requires yeast, warm conditions of approximately 30 °C (so the enzymes are active but not denatured), and anaerobic conditions (absence of oxygen) to prevent ethanol from oxidizing into ethanoic acid.

1 mark for correct choice B.

During the electrolysis of molten lead(II) bromide, lead ions (\(Pb^{2+}\)) gain electrons at the cathode (negative electrode) to form molten lead metal (a silver-grey liquid). Bromide ions (\(Br^-\)) lose electrons at the anode (positive electrode) to form bromine gas (brown fumes).

1 mark for correct choice B.

At \(25^\circ\text{C}\), which is between the melting point of \(-7^\circ\text{C}\) and the boiling point of \(59^\circ\text{C}\), substance Y exists as a liquid. In a liquid, the particles are close together but can move by sliding over one another. Therefore, option B is correct.

1 mark for B.

The proton number (atomic number) is 15, which means there are 15 protons and, in a neutral atom, 15 electrons. The nucleon number (mass number) is 31, so the number of neutrons is \(31 - 15 = 16\).

1 mark for B.

Carbon dioxide has two double covalent bonds (\(\text{O}=\text{C}=\text{O}\)), which corresponds to 4 shared pairs of electrons. Water has two single covalent bonds (\(\text{H}-\text{O}-\text{H}\)), which corresponds to 2 shared pairs of electrons.

1 mark for B.

In this reaction, copper(II) oxide loses oxygen to form copper metal, so it is reduced. Hydrogen gas gains oxygen to form water, so it is oxidized.

1 mark for B.

In concentrated aqueous sodium chloride, chloride ions (\(\text{Cl}^-\)) are discharged at the anode to form chlorine gas. Hydrogen ions (\(\text{H}^+\)) from water are discharged preferentially at the cathode instead of sodium ions (\(\text{Na}^+\)) because hydrogen is lower in the reactivity series, forming hydrogen gas.

1 mark for A.

X + Z sulfate -> no reaction means Z is more reactive than X (\(\text{Z} > \text{X}\)). Y + X sulfate -> reaction occurs means Y is more reactive than X (\(\text{Y} > \text{X}\)). Z + Y sulfate -> reaction occurs means Z is more reactive than Y (\(\text{Z} > \text{Y}\)). Combining these observations gives the order: \(\text{Z} > \text{Y} > \text{X}\).

1 mark for D.

Poly(ethene) is formed by addition polymerisation of ethene monomers, which contain double bonds. Nylon, terylene, and proteins are all formed by condensation polymerisation.

1 mark for C.

Zinc powder has a larger total surface area than zinc lumps, meaning more collisions occur per second, leading to a faster rate of reaction. Since both reactions use the same mass of zinc and excess acid, they will eventually produce the exact same volume of hydrogen gas.

1 mark for B.

At \(20^\circ\text{C}\), a substance is a gas if both its melting point and boiling point are below \(20^\circ\text{C}\). For substance X, its melting point is \(-183^\circ\text{C}\) and its boiling point is \(-161^\circ\text{C}\). Since \(20^\circ\text{C}\) is above the boiling point, it exists as a gas.

Award 1 mark for the correct option B.

The nucleus contains only protons and neutrons. The proton number is 19, so there are 19 protons. The number of neutrons is the nucleon number minus the proton number: \(39 - 19 = 20\) neutrons.

Award 1 mark for identifying the correct nuclear composition as option A.

Methane (\(\text{CH}_4\)) has four single covalent C-H bonds, which correspond to 4 shared pairs of electrons. Water (\(\text{H}_2\text{O}\)) has two single covalent O-H bonds, which correspond to 2 shared pairs of electrons.

Award 1 mark for selecting the correct number of shared pairs of electrons for both molecules as option A.

An endothermic reaction absorbs heat energy from the surroundings, causing the temperature of the reaction mixture to decrease. In reaction 1, the temperature drops from \(21^\circ\text{C}\) to \(15^\circ\text{C}\), indicating it is endothermic.

Award 1 mark for selecting reaction 1 as the endothermic reaction (A).

In this reaction, copper(II) oxide (\(\text{CuO}\)) loses oxygen to become copper (\(\text{Cu}\)). Loss of oxygen is defined as reduction. Therefore, copper(II) oxide is reduced.

Award 1 mark for the correct statement that copper(II) oxide is reduced because of oxygen loss.

Non-metal oxides such as sulfur dioxide (\(\text{SO}_2\)) are acidic. Metal oxides such as calcium oxide (\(\text{CaO}\)) are basic. This matches the classification in Row A.

Award 1 mark for the row that correctly classifies both oxides (Row A).

According to the reactivity series, magnesium is the most reactive metal among those listed (reactivity order: Mg > Zn > Fe > Cu). Therefore, magnesium reacts most vigorously with dilute hydrochloric acid.

Award 1 mark for identifying magnesium as the most reactive metal with acid.

Filtration is the standard method used to separate an insoluble solid (residue) from a liquid or solution (filtrate).

Award 1 mark for identifying filtration as the separation technique.

Helium has a lower relative molecular mass (\(4\)) than carbon dioxide (\(44\)), so its particles move and diffuse faster. The rate of diffusion increases as temperature increases because the particles gain more kinetic energy. Therefore, helium at the higher temperature of \(80\ ^\circ\text{C}\) will diffuse the fastest.

1 mark for the correct option.

The number of neutrons is calculated by subtracting the proton number from the nucleon number: \(31 - 15 = 16\) neutrons. For a neutral atom, the number of electrons is equal to the proton number, which is 15. Thus, there are 16 neutrons and 15 electrons.

1 mark for the correct option.

One molecule of methane, \(\text{CH}_4\), has 4 single covalent bonds, meaning there are 4 shared pairs of electrons. One molecule of water, \(\text{H}_2\text{O}\), has 2 single covalent bonds, meaning there are 2 shared pairs of electrons.

1 mark for the correct option.

An endothermic reaction absorbs thermal energy from the surroundings, causing the temperature of the reaction mixture to decrease. Only reaction 1 shows a decrease in temperature (from \(21\ ^\circ\text{C}\) to \(18\ ^\circ\text{C}\)).

1 mark for the correct option.

Calcium is a metal, so its oxide (calcium oxide, \(\text{CaO}\)) is basic. Carbon is a non-metal, so its oxide (carbon dioxide, \(\text{CO}_2\)) is acidic.

1 mark for the correct option.

Chlorine is more reactive than bromine, so it can displace bromide ions from potassium bromide to form bromine and potassium chloride. However, chlorine is less reactive than fluorine, so it cannot displace fluoride ions from potassium fluoride.

1 mark for the correct option.

Fermentation involves the anaerobic breakdown of glucose into ethanol and carbon dioxide, catalyzed by enzymes in yeast at mild temperatures (around \(30-40\ ^\circ\text{C}\)). It does not use phosphoric acid (which is used in the catalytic hydration of ethene) and must be carried out in the absence of oxygen.

1 mark for the correct option.

Sulfur dioxide (\(\text{SO}_2\)) is released when fossil fuels containing sulfur impurities are burned. It dissolves in rainwater to form acid rain. Carbon monoxide and methane do not cause acid rain. While nitrogen dioxide also contributes to acid rain, it is mainly formed from the reaction of nitrogen and oxygen in car engines, not directly from sulfur impurities in fuels.

1 mark for the correct option.

Diffusion of gas particles is faster at higher temperatures because the particles have more kinetic energy. Additionally, lighter gas particles diffuse faster than heavier gas particles. Helium (
\(M_r = 4\)
) is lighter than argon (
\(M_r = 40\)
). Therefore, helium gas at
\(80^\circ\text{C}\)
will diffuse most rapidly.

Award 1 mark for selecting B.

Carbon has an atomic number of 6, which means every carbon atom contains 6 protons. In a neutral atom, the number of electrons is equal to the number of protons, so it has 6 electrons. The nucleon number is the total number of protons and neutrons. The number of neutrons is found by subtracting the atomic number from the nucleon number:
\(14 - 6 = 8\)
.

Award 1 mark for selecting A.

During the electrolysis of molten lead(II) bromide,
\(\text{Pb}^{2+}\)
ions are attracted to the negative electrode (cathode) where they gain electrons to form lead metal, observed as a grey liquid bead.
\(\text{Br}^-\)
ions are attracted to the positive electrode (anode) where they lose electrons to form bromine gas, observed as a brown vapour.

Award 1 mark for selecting A.

The rate of a chemical reaction is decreased by lowering the concentration of reactants and decreasing the surface area of solid reactants. Large lumps of calcium carbonate have a smaller surface area than powder, which slows the rate of reaction. A lower concentration of hydrochloric acid (
\(0.5\text{ mol/dm}^3\)
compared to
\(2.0\text{ mol/dm}^3\)
) also slows the rate of reaction.

Award 1 mark for selecting D.

A metal can only displace another metal from its compound if it is more reactive. According to the reactivity series:
\(\text{Mg} > \text{Zn} > \text{Fe} > \text{Cu}\)
. Zinc is more reactive than iron and copper, so it will displace them from their sulfate solutions. Zinc is less reactive than magnesium, so it cannot displace magnesium.

Award 1 mark for selecting B.

Carbon monoxide (
\(\text{CO}\)
) is formed when carbon-containing fuels burn in a limited supply of oxygen (incomplete combustion). It is highly toxic because it binds strongly to haemoglobin in red blood cells, preventing oxygen from being transported around the body.

Award 1 mark for selecting B.

As Group VII is descended, the elements become less reactive because the outer shell is further from the nucleus, making it harder to attract an electron. The colours of the elements also become progressively darker (from pale yellow fluorine to dark grey/black iodine).

Award 1 mark for selecting A.

The rapid decolourisation of bromine water (from orange/brown to colourless) is the test for unsaturation. This indicates that the organic compound contains a carbon-carbon double bond (
\(\text{C=C}\)
) and is therefore an alkene.

Award 1 mark for selecting B.

The rate of diffusion of a gas is inversely proportional to the square root of its relative molecular mass. Since the mass of helium is 4 and the mass of methane is 16, the ratio of their rates of diffusion is the square root of (16 / 4) which equals 2. Therefore, helium diffuses twice as fast as methane.

1 mark for the correct option C.

First, calculate the relative formula mass of ethane, \(C_2H_6 = (2 \times 12) + (6 \times 1) = 30\text{ g/mol}\). The number of moles of ethane is \(3.0\text{ g} / 30\text{ g/mol} = 0.10\text{ mol}\). According to the balanced equation, \(2\text{ moles}\) of ethane react with \(7\text{ moles}\) of oxygen. Therefore, \(0.10\text{ mol}\) of ethane requires \(0.10 \times \frac{7}{2} = 0.35\text{ mol}\) of oxygen. The volume of oxygen at r.t.p. is \(0.35\text{ mol} \times 24\text{ dm}^3/\text{mol} = 8.4\text{ dm}^3\).

Award 1 mark for the correct option C.

At higher temperatures, the average kinetic energy of the reactant particles increases. Consequently, a greater proportion of the colliding particles possess energy equal to or greater than the activation energy, leading to a higher frequency of successful collisions.

Award 1 mark for the correct option C.

In concentrated aqueous sodium chloride, the ions present are \(Na^+\), \(H^+\), \(Cl^-\), and \(OH^-\). Hydrogen ions are discharged preferentially at the negative cathode because hydrogen is less reactive than sodium, producing hydrogen gas. Chloride ions are in high concentration and are discharged preferentially at the positive anode, producing chlorine gas.

Award 1 mark for the correct option C.

The forward reaction is exothermic, so raising the temperature shifts the equilibrium to the left (decreasing the yield of \(SO_3\)). There are more moles of gas on the reactant side (3 moles) than the product side (2 moles), so decreasing the pressure shifts the equilibrium to the left. Therefore, high temperature and low pressure yield the lowest percentage of sulfur trioxide.

Award 1 mark for the correct option B.

Propan-1-ol is a primary alcohol. Heating it under reflux with a strong oxidizing agent like acidified potassium manganate(VII) fully oxidizes it to the corresponding carboxylic acid, which is propanoic acid, \(CH_3CH_2COOH\).

Award 1 mark for the correct option C.

These properties are characteristic of a giant ionic lattice. The high melting point is due to strong electrostatic forces between oppositely charged ions. It conducts electricity when molten because the ions are free to move, but not when solid because the ions are held in fixed positions in the lattice.

Award 1 mark for the correct option B.

As you descend Group VII, the elements become less reactive because the atomic radius increases and the outer shell is further from the nucleus, making it harder to attract an incoming electron. Additionally, the intensity of the color increases (they become darker, from pale yellow to dark grey/black).

Award 1 mark for the correct option B.

Oxidation involves an increase in oxidation state. In reaction B, the oxidation state of iron (Fe) increases from 0 (in the element \(Fe\)) to +2 (in \(Fe^{2+}\)). In all other options, the underlined species undergo reduction (a decrease in oxidation state).

Award 1 mark for the correct option B.

Let the fractional abundance of \(^{121}\text{Z}\) be \(x\). Therefore, the abundance of \(^{123}\text{Z}\) is \(1 - x\). We can set up the equation for the relative atomic mass: \(121x + 123(1 - x) = 121.80\). Simplifying this gives: \(121x + 123 - 123x = 121.80 \Rightarrow 123 - 2x = 121.80 \Rightarrow 2x = 1.20 \Rightarrow x = 0.60\). Thus, the percentage abundance of \(^{121}\text{Z}\) is 60%.

Award 1 mark for the correct option C. Reject other options.

During the electrolysis of concentrated aqueous sodium bromide, \(\text{Br}^-\text{(aq)}\) ions are discharged at the anode (positive electrode) to form bromine gas/liquid (\(\text{Br}_2\)). At the cathode (negative electrode), \(\text{H}^+\text{(aq)}\) ions from water are preferentially discharged over \(\text{Na}^+\text{(aq)}\) ions to produce hydrogen gas (\(\text{H}_2\)).

Award 1 mark for the correct option A. Reject other options.

The rate of a reaction increases when the surface area of a solid reactant increases (using powder instead of chips), when the concentration of the acid increases, and when the temperature increases. Option A combines all these factors for the highest rate: powder, \(2.0\text{ mol/dm}^3\), and \(40^\circ\text{C}\).

Award 1 mark for the correct option A. Reject other options.

Since the forward reaction is exothermic, a lower temperature shifts the equilibrium to the right to favor \(\text{SO}_3\) production. There are 3 moles of gas on the left and 2 moles of gas on the right, so a higher pressure shifts the equilibrium to the side with fewer gas moles (the right), yielding more \(\text{SO}_3\).

Award 1 mark for the correct option C. Reject other options.

A metal reacts with an acid to produce a salt and hydrogen gas. Ethanoic acid reacts with magnesium to form magnesium ethanoate, \(\text{(CH}_3\text{COO)}_2\text{Mg}\), and hydrogen gas, \(\text{H}_2\).

Award 1 mark for the correct option A. Reject other options.

We find the relative molecular mass (\(M_r\)) of the alkane gas by multiplying its density by the molar volume of a gas at r.t.p.: \(M_r = 1.25\text{ g/dm}^3 \times 24\text{ dm}^3\text{/mol} = 30\text{ g/mol}\). The alkane with \(M_r = 30\) is ethane (\(\text{C}_2\text{H}_6\)), because \((2 \times 12) + (6 \times 1) = 30\).

Award 1 mark for the correct option B. Reject other options.

The stable ion \(E^{2-}\) has a total of 18 electrons (2 + 8 + 8). Since it has a negative charge of 2, the neutral atom E must have 2 fewer electrons than the ion, which is \(18 - 2 = 16\) electrons. The proton number of E is equal to the number of electrons in a neutral atom, which is 16.

Award 1 mark for the correct option A. Reject other options.

To calculate the energy change: 1) Energy needed to break reactant bonds = \(\text{H–H} + \text{Cl–Cl} = 436 + 242 = +678\text{ kJ/mol}\). 2) Energy released when forming product bonds = \(2 \times \text{H–Cl} = 2 \times 431 = 862\text{ kJ/mol}\). 3) Overall energy change \(\Delta H = 678 - 862 = -184\text{ kJ/mol}\).

Award 1 mark for the correct option A. Reject other options.

First, calculate the number of moles of carbon dioxide gas produced:
\[\text{moles of CO}_2 = \frac{1.08\text{ dm}^3}{24.0\text{ dm}^3/\text{mol}} = 0.045\text{ mol}\]

According to the chemical equation:
\[\text{CaCO}_3(\text{s}) + 2\text{HCl}(\text{aq}) \rightarrow \text{CaCl}_2(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g})\]
The molar ratio of \(\text{CaCO}_3\) to \(\text{CO}_2\) is \(1:1\). Therefore, the number of moles of pure \(\text{CaCO}_3\) in the sample is \(0.045\text{ mol}\).

Next, calculate the mass of pure calcium carbonate:
\[\text{mass of CaCO}_3 = 0.045\text{ mol} \times 100\text{ g/mol} = 4.50\text{ g}\]

Finally, calculate the percentage purity of the sample:
\[\text{percentage purity} = \frac{4.50\text{ g}}{5.00\text{ g}} \times 100\% = 90.0\%\]

Award 1 mark for the correct answer (C).
- 1 mark: correct calculation of moles of \(\text{CO}_2\) (\(0.045\text{ mol}\)), mass of pure \(\text{CaCO}_3\) (\(4.50\text{ g}\)), and percentage purity (\(90.0\%\)).

During the electrolysis of concentrated aqueous copper(II) chloride:
- At the anode (positive electrode): Chloride ions (\(\text{Cl}^-\)) are discharged in preference to hydroxide ions (\(\text{OH}^-\)) because the solution is concentrated, forming chlorine gas (\(\text{Cl}_2\)).
- At the cathode (negative electrode): Copper(II) ions (\(\text{Cu}^{2+}\)) are discharged in preference to hydrogen ions (\(\text{H}^+\)) because copper is lower in the reactivity series, forming copper metal (\(\text{Cu}\)).
- As \(\text{Cu}^{2+}\) and \(\text{Cl}^-\) ions are selectively removed, the concentrations of \(\text{H}^+\) and \(\text{OH}^-\) remain equal and balanced (as in neutral water), so the pH of the solution remains virtually unchanged.

Award 1 mark for the correct answer (B).
- 1 mark: correctly identifying chlorine at the anode, copper at the cathode, and that pH remains virtually unchanged.

- A is correct: Decreasing the temperature decreases the kinetic energy of particles, which decreases the rate of both forward and reverse reactions. However, because the forward reaction is exothermic, a lower temperature shifts the position of equilibrium to the right, increasing the equilibrium yield of \(\text{SO}_3\).
- B is incorrect: Increasing pressure increases the rate of both reactions and shifts the equilibrium to the right (fewer gas moles), increasing the yield.
- C is incorrect: Removing a catalyst increases the activation energy but has no effect on the position of equilibrium or the yield.
- D is incorrect: Increasing temperature shifts the equilibrium to the left, decreasing the yield of \(\text{SO}_3\).

Award 1 mark for the correct answer (A).
- 1 mark: correct understanding of the contrasting effects of temperature on rate of reaction versus position of equilibrium for an exothermic reaction.

Chlorine is more reactive than bromine, so it displaces bromide ions from potassium bromide solution:
\[\text{Cl}_2(\text{aq}) + 2\text{KBr}(\text{aq}) \rightarrow 2\text{KCl}(\text{aq}) + \text{Br}_2(\text{aq})\]
Potassium bromide (\(\text{KBr}\)) is a colorless solution, and the formation of bromine (\(\text{Br}_2\)) causes the solution to turn orange-brown.
- A is incorrect: Fluorine is more reactive than chlorine, so no reaction occurs.
- B is incorrect: Bromine is less reactive than chlorine, so no reaction occurs. Furthermore, bromine water is already orange-brown.
- D is incorrect: Iodine is less reactive than bromine, so no reaction occurs.

Award 1 mark for the correct answer (C).
- 1 mark: correctly identifying the mixture where a displacement reaction occurs to form bromine (\(\text{Br}_2\)), causing the observed color change.

The polymer structure shows ester linkages (\(\text{---O---CO---}\)) repeating along the chain. This indicates that the polymer is a polyester (specifically terylene-like or polyethylene adipate-like). Polyesters are synthetic condensation polymers formed by the reaction of a dicarboxylic acid and a diol, with the elimination of water molecules.
- A is incorrect because addition polymerisation yields carbon-only main chains.
- B is incorrect because polyamides contain amide linkages (\(\text{---NH---CO---}\)).
- D is incorrect because sugars are formed from carbohydrates (like starch), not polyesters.

Award 1 mark for the correct answer (C).
- 1 mark: identifying the ester linkage and classifying the polymer as a polyester formed by condensation polymerisation.

First, identify the limiting reactant.
- Moles of \(\text{CaCO}_3 = \frac{2.0\text{ g}}{100\text{ g/mol}} = 0.02\text{ mol}\).
- Moles of \(\text{HCl} = 0.050\text{ dm}^3 \times 1.0\text{ mol/dm}^3 = 0.05\text{ mol}\).
Since the stoichiometry is \(1:2\), \(0.02\text{ mol}\) of \(\text{CaCO}_3\) requires \(0.04\text{ mol}\) of \(\text{HCl}\).
As \(0.05\text{ mol}\) of \(\text{HCl}\) is available, \(\text{HCl}\) is in excess, and \(\text{CaCO}_3\) is the limiting reactant.
Therefore, the total volume of \(\text{CO}_2\) produced depends entirely on the mass of \(\text{CaCO}_3\).
To achieve a higher initial rate but keep the same total volume of gas:
- We can increase the surface area of \(\text{CaCO}_3\) by using powder instead of chips (this increases the rate).
- We must keep the mass of \(\text{CaCO}_3\) at \(2.0\text{ g}\) (to keep the volume of gas the same).
This matches the conditions in Option A.

Award 1 mark for the correct answer (A).
- 1 mark: correct application of collision theory (surface area increases rate) and stoichiometry (mass of limiting reactant determines product volume).

Let \(x\) represent the percentage abundance of the \(^{11}\text{B}\) isotope (expressed as a fraction between \(0\) and \(1\)).
The abundance of the \(^{10}\text{B}\) isotope is therefore \(1 - x\).

Using the formula for relative atomic mass:
\[(11 \times x) + 10 \times (1 - x) = 10.8\]
\[11x + 10 - 10x = 10.8\]
\[x = 0.8\]

Convert the fraction to a percentage:
\[0.8 \times 100\% = 80\%\]

Award 1 mark for the correct answer (C).
- 1 mark: correct calculation of the isotopic abundance from the relative atomic mass.

- A primary alcohol is oxidised to a carboxylic acid by acidified potassium manganate(VII). Carboxylic acids react with carbonates (such as sodium carbonate) to produce carbon dioxide gas. This indicates the reactant is a primary alcohol.
- The dehydration of the alcohol yields propene, which is an alkene with 3 carbon atoms. Therefore, the alcohol must also have 3 carbon atoms.
- Propan-1-ol is a primary alcohol with 3 carbon atoms. On oxidation, it forms propanoic acid, and on dehydration, it forms propene.
- Propan-2-ol is a secondary alcohol. On oxidation, it forms propanone (a ketone), which does not react with sodium carbonate to produce carbon dioxide gas.
Hence, the organic compound is propan-1-ol.

Award 1 mark for the correct answer (B).
- 1 mark: correctly identifying the 3-carbon primary alcohol based on its oxidation and dehydration products.

First, write the balanced chemical equation for the combustion of propane: \(\text{C}_3\text{H}_8\text{(g)} + 5\text{O}_2\text{(g)} \rightarrow 3\text{CO}_2\text{(g)} + 4\text{H}_2\text{O}\text{(l)}\). Calculate the number of moles of propane burned: \(\text{moles of } \text{C}_3\text{H}_8 = \frac{4.4\text{ g}}{44\text{ g/mol}} = 0.1\text{ mol}\). According to the stoichiometric ratio, 1 mole of \(\text{C}_3\text{H}_8\) produces 3 moles of \(\text{CO}_2\). Therefore, \(\text{moles of } \text{CO}_2 = 3 \times 0.1\text{ mol} = 0.3\text{ mol}\). Finally, calculate the volume of \(\text{CO}_2\) at r.t.p.: \(\text{Volume} = 0.3\text{ mol} \times 24\text{ dm}^3\text{/mol} = 7.2\text{ dm}^3\).

1 mark: B is the correct option. Method: mole calculations and stoichiometry must lead directly to 7.2 dm3.

When copper electrodes are used in the electrolysis of aqueous copper(II) sulfate, the anode (positive electrode) is active. Copper atoms from the anode are oxidised to form copper(II) ions: \(\text{Cu(s)} \rightarrow \text{Cu}^{2+}\text{(aq)} + 2\text{e}^-\). Simultaneously, copper(II) ions in solution are reduced at the cathode to form copper metal: \(\text{Cu}^{2+}\text{(aq)} + 2\text{e}^- \rightarrow \text{Cu(s)}\). As a result, the concentration of copper(II) ions in the electrolyte remains constant, the anode loses mass, and the cathode gains mass.

1 mark: D is the correct option. Correct oxidation process at the active anode identified.

Increasing the concentration of the acid (option B) increases the number of reacting particles per unit volume, which increases the frequency of collisions. It does not alter the temperature, so the kinetic energy distribution of the particles and the proportion of particles with energy greater than the activation energy remain unchanged. Raising the temperature (option C) or adding a catalyst (option A) changes the energy characteristics of the system.

1 mark: B is the correct option. Analysis of collision theory principles reveals concentration increases collision frequency without affecting energy distribution.

According to Le Chatelier's principle: 1. The forward reaction is exothermic (\(\Delta H < 0\)), so a lower temperature shifts the equilibrium position to the right to favor the forward reaction, increasing the yield of \(\text{SO}_3\). 2. There are 3 moles of gaseous reactants on the left and 2 moles of gaseous products on the right. An increase in pressure shifts the equilibrium position to the side with fewer gas moles (the right), increasing the yield of \(\text{SO}_3\). Therefore, low temperature and high pressure yield the maximum sulfur trioxide.

1 mark: C is the correct option. Application of temperature and pressure shifts on a gaseous exothermic reversible reaction.

Propanoic acid (\(\text{CH}_3\text{CH}_2\text{COOH}\)) and ethanol (\(\text{CH}_3\text{CH}_2\text{OH}\)) undergo condensation (esterification) to produce the ester ethyl propanoate (\(\text{CH}_3\text{CH}_2\text{COOCH}_2\text{CH}_3\)) and water. The naming convention is derived from the alcohol (ethyl) and the carboxylic acid (propanoate).

1 mark: A is the correct option. Correct ester identification and structural formula.

Sodium chloride and ammonium chloride are soluble in water, whereas sand (silicon(IV) oxide) is giant covalent and insoluble. Adding water dissolves the salts, leaving sand as a solid suspension. Filtering this mixture leaves the sand as residue on the filter paper. Washing the residue with distilled water removes any remaining salt solution, and drying the residue yields pure, dry sand.

1 mark: A is the correct option. Correct process to separate insoluble residue from soluble solutes.

In the ionic compound \(\text{YF}_2\), since fluorine forms a 1- ion (\(\text{F}^-\)), the element \(\text{Y}\) must form a 2+ cation (\(\text{Y}^{2+}\)). Since \(\text{Y}\) is in Period 3 and forms a 2+ ion, it must be magnesium (atomic number 12). A neutral magnesium atom has the configuration 2, 8, 2. After losing 2 valence electrons to form \(\text{Mg}^{2+}\), its electronic configuration becomes 2, 8.

1 mark: A is the correct option. Deduce ion charge, identify Period 3 element, and specify correct ionic configuration.

In the reaction, carbon monoxide (\(\text{CO}\)) reduces iron(III) oxide (\(\text{Fe}_2\text{O}_3\)) by removing oxygen from it, forming carbon dioxide (\(\text{CO}_2\)). Thus, the carbon in \(\text{CO}\) increases its oxidation state from +2 to +4, meaning it is oxidised. The species that gets oxidised acts as the reducing agent. Therefore, \(\text{CO}\) is the reducing agent.

1 mark: B is the correct option. Identify reducing agent via oxidation state change or oxygen transfer.