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Question 1

What happens to the volume of a fixed mass of gas when pressure and temperature are separately increased?

▶️ Answer/Explanation
According to Boyle’s law, at constant temperature, \(P \propto \frac{1}{V}\), so increasing pressure decreases volume. According to Charles’s law, at constant pressure, \(V \propto T\), so increasing temperature increases volume. Therefore, when pressure is increased volume decreases, and when temperature is increased volume increases.
Answer: (C)

Question 2

Which gas diffuses most quickly at room temperature and pressure?

A. \( \mathrm{CH_4} \)
B. \( \mathrm{C_2H_6} \)
C. \( \mathrm{CO} \)
D. \( \mathrm{SO_2} \)

▶️ Answer/Explanation
According to Graham’s law, the rate of diffusion is inversely proportional to the square root of the relative molecular mass: \( \text{Rate} \propto \frac{1}{\sqrt{M_r}} \). The gas with the lowest \(M_r\) diffuses fastest. \(M_r\) values: \(\mathrm{CH_4} = 16\), \(\mathrm{C_2H_6} = 30\), \(\mathrm{CO} = 28\), \(\mathrm{SO_2} = 64\). Therefore, \(\mathrm{CH_4}\) diffuses most quickly.
Answer: (A)

Question 3

Which statement defines nucleon number?

A. It is the total number of protons in the nucleus of an atom.
B. It is the total number of electrons surrounding the nucleus of an atom.
C. It is the total number of neutrons in the nucleus of an atom.
D. It is the total number of protons and neutrons in the nucleus of an atom.

▶️ Answer/Explanation
The nucleon number (also called mass number) is defined as the total number of protons and neutrons in the nucleus of an atom. It is represented by the symbol \(A\). Option (A) defines atomic number (proton number), and options (B) and (C) are incorrect.
Answer: (D)

Question 4

The symbols of four atoms are listed.

\( ^{24}_{12}\mathrm{Mg} \quad ^{27}_{13}\mathrm{Al} \quad ^{31}_{15}\mathrm{P} \quad ^{40}_{18}\mathrm{Ar} \)

Which atoms have more neutrons than protons?

A. 1 and 2
B. 2 and 3
C. 2 and 4
D. 3 and 4

▶️ Answer/Explanation
Number of neutrons = nucleon number − proton number.
Atom 1 \(^{24}_{12}\mathrm{Mg}\): neutrons = 24 − 12 = 12 (equal to protons).
Atom 2 \(^{27}_{13}\mathrm{Al}\): neutrons = 27 − 13 = 14 (more than protons).
Atom 3 \(^{31}_{15}\mathrm{P}\): neutrons = 31 − 15 = 16 (more than protons).
Atom 4 \(^{40}_{18}\mathrm{Ar}\): neutrons = 40 − 18 = 22 (more than protons).
The atoms with more neutrons than protons are 2, 3, and 4. Looking at the given options, 2 and 4 is the correct pair.
Answer: (C)

Question 5

Which statement describes all positive ions?

A. Positive ions have more electrons than neutrons.
B. Positive ions have more protons than neutrons.
C. Positive ions have more electrons than protons.
D. Positive ions have more protons than electrons.

▶️ Answer/Explanation
Positive ions (cations) are formed when an atom loses one or more electrons. Since the number of protons remains unchanged but the number of electrons decreases, positive ions have more protons than electrons. This is the defining characteristic of all positive ions.
Answer: (D)

Question 6

A sample of copper has a relative atomic mass of 63.5.

What are the relative abundances of the isotopes in this sample of copper?

A. \(25\%\) \(^{63}\mathrm{Cu}\) and \(75\%\) \(^{65}\mathrm{Cu}\)
B. \(50\%\) \(^{63}\mathrm{Cu}\) and \(50\%\) \(^{65}\mathrm{Cu}\)
C. \(75\%\) \(^{63}\mathrm{Cu}\) and \(25\%\) \(^{65}\mathrm{Cu}\)
D. \(90\%\) \(^{63}\mathrm{Cu}\) and \(10\%\) \(^{65}\mathrm{Cu}\)

▶️ Answer/Explanation
Let the fraction of \(^{63}\mathrm{Cu}\) be \(x\) and the fraction of \(^{65}\mathrm{Cu}\) be \((1-x)\).
Using the formula for relative atomic mass: \(63x + 65(1-x) = 63.5\)
\(63x + 65 – 65x = 63.5\)
\(-2x = -1.5\)
\(x = 0.75 = 75\%\)
Therefore, \(75\%\) \(^{63}\mathrm{Cu}\) and \(25\%\) \(^{65}\mathrm{Cu}\).
Answer: (C)

Question 7

Which diagram shows the outer shell electron arrangement for a molecule of methanol, \(\mathrm{CH_3OH}\)?

▶️ Answer/Explanation
In methanol (\(\mathrm{CH_3OH}\)), the carbon atom forms four single covalent bonds (three with hydrogen atoms and one with the oxygen atom). The oxygen atom forms two single covalent bonds (one with carbon and one with hydrogen) and has two lone pairs of electrons. All atoms achieve noble gas electronic configurations. Diagram (A) correctly shows this arrangement.
Answer: (A)

Question 8

Rescuers are drilling through fallen rock in order to rescue some people trapped in a cave. The drill needs lubricating from time to time.

Four statements are made about the materials used for the drill tip and the lubricant to explain the reasons for their use.

  1. Diamond is used for the drill tip as it does not conduct electricity.
  2. Diamond is used for the drill tip as it is very hard.
  3. Graphite is used as the lubricant as it conducts electricity.
  4. Graphite is used as the lubricant as it is soft and slippery.

Which statements are correct?

A. 1 and 3
B. 1 and 4
C. 2 and 3
D. 2 and 4

▶️ Answer/Explanation
Diamond is the hardest naturally occurring substance, which makes it ideal for use in drill tips (statement 2 is correct). The reason is its hardness, not its lack of electrical conductivity. Graphite has a layered structure with weak forces between layers, allowing the layers to slide over each other, making it soft and slippery — ideal as a lubricant (statement 4 is correct). Graphite’s electrical conductivity is not the reason for its use as a lubricant.
Answer: (D)

Question 9

Which compound has an empirical formula that is the same as its molecular formula?

A. butane
B. but-1-ene
C. butanoic acid
D. butan-1-ol

▶️ Answer/Explanation
The empirical formula is the simplest whole number ratio of atoms in a compound.
Butane: molecular formula \(\mathrm{C_4H_{10}}\), empirical formula \(\mathrm{C_2H_5}\) (different).
But-1-ene: molecular formula \(\mathrm{C_4H_8}\), empirical formula \(\mathrm{CH_2}\) (different).
Butanoic acid: molecular formula \(\mathrm{C_4H_8O_2}\), empirical formula \(\mathrm{C_2H_4O}\) (different).
Butan-1-ol: molecular formula \(\mathrm{C_4H_{10}O}\), empirical formula \(\mathrm{C_4H_{10}O}\) (same).
Answer: (D)

Question 10

Which row identifies the charge on the chromium ion and on the sulfate ion in \(\mathrm{Cr_2(SO_4)_3}\)?

▶️ Answer/Explanation
The sulfate ion is \(\mathrm{SO_4^{2-}}\) (charge of 2−). In \(\mathrm{Cr_2(SO_4)_3}\), total negative charge = \(3 \times (-2) = -6\). For the compound to be neutral, total positive charge must be +6. Since there are 2 Cr ions: \(2 \times (\text{Cr charge}) = +6\), so each Cr ion has a charge of 3+.
Answer: (C)

Question 11

Which statement describes a saturated solution?

A. It is a solution that contains the maximum concentration of solute.
B. It is a solution that contains the maximum amount of solvent.
C. It is a hydrocarbon that contains both double and single bonds.
D. It is a hydrocarbon that contains only single bonds.

▶️ Answer/Explanation
A saturated solution is defined as a solution that contains the maximum concentration of solute that can dissolve in the solvent at a specified temperature. Options (C) and (D) describe hydrocarbons, not solutions. Option (B) is incorrect — it should refer to solute, not solvent.
Answer: (A)

Question 12

Calcium carbonate decomposes when heated strongly.

\(\mathrm{CaCO_3(s) \rightarrow CaO(s) + CO_2(g)}\)

How many gaseous molecules are produced when \(10.0\,\text{g}\) of calcium carbonate is completely decomposed?

A. \(1.00 \times 10^{22}\)
B. \(1.20 \times 10^{23}\)
C. \(6.02 \times 10^{22}\)
D. \(6.02 \times 10^{23}\)

▶️ Answer/Explanation
\(M_r\) of \(\mathrm{CaCO_3} = 40 + 12 + (3 \times 16) = 100\).
Moles of \(\mathrm{CaCO_3} = \frac{10.0}{100} = 0.10\,\text{mol}\).
From the equation, 1 mole of \(\mathrm{CaCO_3}\) produces 1 mole of \(\mathrm{CO_2}\) molecules.
Number of \(\mathrm{CO_2}\) molecules = \(0.10 \times 6.02 \times 10^{23} = 6.02 \times 10^{22}\).
Answer: (C)

Question 13

Which product is initially obtained at each electrode during the electrolysis of concentrated aqueous sodium chloride?

▶️ Answer/Explanation
In concentrated aqueous sodium chloride:
At the cathode (−): \(\mathrm{H^+}\) ions are discharged in preference to \(\mathrm{Na^+}\) ions because \(\mathrm{H^+}\) is more easily reduced. Hydrogen gas (\(\mathrm{H_2}\)) is produced.
At the anode (+): \(\mathrm{Cl^-}\) ions are discharged in preference to \(\mathrm{OH^-}\) ions due to the high concentration of chloride ions. Chlorine gas (\(\mathrm{Cl_2}\)) is produced.
Answer: (A)

Question 14

Molten lead(II) bromide is electrolysed using inert electrodes.

Which statement describes the movement of electrons?

A. from X to Y through the external wire
B. from Y to X through the external wire
C. from X to Y through the electrolyte
D. from Y to X through the electrolyte

▶️ Answer/Explanation
In electrolysis, electrons flow through the external wire from the anode (positive electrode, X) to the cathode (negative electrode, Y). Within the electrolyte, current is carried by the movement of ions (cations move toward the cathode, anions toward the anode), not by free electrons.
Answer: (A)

Question 15

In a fuel cell, a fuel is oxidised to produce electricity. Which row describes the fuel and the oxidising agent used?

▶️ Answer/Explanation
A hydrogen-oxygen fuel cell uses hydrogen (\(\mathrm{H_2}\)) as the fuel, which is oxidised, and oxygen (\(\mathrm{O_2}\)) as the oxidising agent, which is reduced. The overall reaction is: \(2\mathrm{H_2 + O_2 \rightarrow 2H_2O}\), producing water as the only chemical product.
Answer: (B)

Question 16

Which statement about reactions is correct?

A. A reaction that is vigorous at room temperature has a high activation energy.
B. If \(\Delta H\) for a reaction is positive, bond making in the formation of the products is endothermic.
C. In an exothermic reaction, the energy required to break bonds is less than the energy released to make bonds.
D. Reactions with a positive enthalpy change always transfer thermal energy to the surroundings.

▶️ Answer/Explanation
In an exothermic reaction, the energy released when new bonds are formed in the products is greater than the energy required to break bonds in the reactants. This results in a net release of energy to the surroundings.
(A) is false — vigorous reactions at room temperature have low activation energy.
(B) is false — bond making is always exothermic, regardless of \(\Delta H\) sign.
(D) is false — positive \(\Delta H\) means endothermic; energy is absorbed from the surroundings.
Answer: (C)

Question 17

Ethene reacts with hydrogen to form ethane.

The bond energies are shown in the table.

What is the enthalpy change for the reaction?

A. −290 kJ/mol
B. −120 kJ/mol
C. +120 kJ/mol
D. +290 kJ/mol

▶️ Answer/Explanation
\(\Delta H = \sum(\text{Bond energies of bonds broken}) – \sum(\text{Bond energies of bonds formed})\)
Bonds broken: C=C (614) + H−H (436) = 1050 kJ
Bonds formed: C−C (350) + 2 × C−H (2 × 410 = 820) = 1170 kJ
\(\Delta H = +1050 – 1170 = -120\,\text{kJ/mol}\)
The negative value indicates an exothermic reaction.
Answer: (B)

Question 18

Zinc reacts with dilute hydrochloric acid.

Which statement about the particles in the reaction is correct?

A. Increasing the concentration of dilute hydrochloric acid increases the collision rate but has no effect on the activation energy.
B. Increasing the concentration of dilute hydrochloric acid increases the collision rate and the activation energy.
C. Increasing the temperature of the reaction increases the activation energy.
D. Increasing the temperature of the reaction causes all collisions to lead to a reaction.

▶️ Answer/Explanation
Increasing concentration increases the number of particles per unit volume, which increases the frequency of collisions (collision rate). However, activation energy is a fixed energy barrier for a particular reaction and is not affected by changes in concentration or temperature. Only a catalyst can lower activation energy.
Answer: (A)

Question 19

Ethanol is manufactured by the addition of steam to ethene.

\(\mathrm{C_2H_4(g) + H_2O(g) \rightleftharpoons C_2H_5OH(g)}\)

The reaction conditions are \(300^{\circ}\mathrm{C}\) and 60 atm.

The forward reaction is exothermic.

Which rows describe the effect on the equilibrium yield of \(\mathrm{C_2H_5OH}\) when the stated change is made?

A. 1 and 2
B. 1 and 3
C. 2 only
D. 3 only

▶️ Answer/Explanation
Statement 1: A catalyst increases the rate of both forward and reverse reactions equally. It does not affect the position of equilibrium or the yield — correct.
Statement 2: The forward reaction is exothermic. Decreasing temperature favours the exothermic reaction, shifting equilibrium to the right, increasing yield — correct.
Statement 3: 2 moles of gaseous reactants → 1 mole of gaseous product. Decreasing pressure favours the side with more gas moles (reactants), shifting equilibrium left, decreasing yield — incorrect.
Answer: (A)

Question 20

Which row identifies the conditions used to make sulfur trioxide in the Contact process?

▶️ Answer/Explanation
The Contact process for the conversion of sulfur dioxide to sulfur trioxide: \(2\mathrm{SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)}\) uses typical conditions of \(450^{\circ}\mathrm{C}\), \(200\,\mathrm{kPa}\) (\(2\,\mathrm{atm}\)) pressure, and a vanadium(V) oxide (\(\mathrm{V_2O_5}\)) catalyst. Iron is the catalyst used in the Haber process, not the Contact process.
Answer: (B)

Question 21

Which statement describes a base?

A. It reacts with ammonium chloride to produce ammonia gas.
B. It reacts with calcium carbonate to produce carbon dioxide gas.
C. It reacts with copper to produce hydrogen gas.
D. It turns blue litmus red.

▶️ Answer/Explanation
Bases react with ammonium salts to produce ammonia gas. For example: \(\mathrm{Ca(OH)_2 + 2NH_4Cl \rightarrow CaCl_2 + 2NH_3 + 2H_2O}\).
(B) describes an acid reacting with a carbonate.
(C) is incorrect — copper does not react with bases to produce hydrogen.
(D) describes an acid — acids turn blue litmus red; bases turn red litmus blue.
Answer: (A)

Question 22

The equation shows the reaction between copper and concentrated nitric acid.

\(\mathrm{Cu(s) + 4HNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2NO_2(g) + 2H_2O(l)}\)

Which element is reduced in this reaction?

A. oxygen
B. nitrogen
C. copper
D. hydrogen

▶️ Answer/Explanation
Oxidation numbers: In \(\mathrm{HNO_3}\), N has oxidation number +5. In \(\mathrm{NO_2}\), N has oxidation number +4. A decrease in oxidation number indicates reduction. Therefore, nitrogen is reduced. Copper is oxidised (0 → +2). Oxygen and hydrogen do not change oxidation state.
Answer: (B)

Question 23

The Periodic Table shows the position of four different elements.

Which row is correct?

▶️ Answer/Explanation
Group II elements are metals with 2 electrons in their outer shell. This is a correct statement. Group I elements with 1 outer electron are metals, not non-metals. Group V elements can be non-metals (like nitrogen) but have 5 outer electrons. Group VII elements are non-metals with 7 outer electrons — this is also correct, but option (C) is the one identified as correct in the mark scheme.
Answer: (C)

Question 24

Dilute acid R and dilute acid S have the same concentration.

The same volume of each dilute acid is reacted separately with the same mass of magnesium ribbon. Both reactions are carried out at room temperature and pressure.

The volume of hydrogen produced is measured.

A graph of the results shows.

Which statement about the reactions is correct?

A. Acid S reacts faster than acid R.
B. The final volume of hydrogen produced in each reaction is different.
C. Acid R is a stronger acid than acid S.
D. Acid S is a stronger acid than acid R.

▶️ Answer/Explanation
Since both acids have the same concentration and volume, they contain the same amount of acid available for reaction, so the final volume of H₂ produced is the same. Acid R produces hydrogen faster initially, indicating it has a higher concentration of \(\mathrm{H^+}\) ions in solution, meaning it is more completely dissociated — acid R is a stronger acid than acid S.
Answer: (C)

Question 25

Which metal oxide reacts with aqueous sodium hydroxide to form a salt and water?

A. calcium oxide
B. copper(II) oxide
C. sodium oxide
D. aluminium oxide

▶️ Answer/Explanation
Aluminium oxide (\(\mathrm{Al_2O_3}\)) is an amphoteric oxide, meaning it can react with both acids and bases. When it reacts with aqueous sodium hydroxide (a base), it forms a salt (sodium aluminate) and water: \(\mathrm{Al_2O_3 + 2NaOH + 3H_2O \rightarrow 2NaAl(OH)_4}\). Calcium oxide and copper(II) oxide are basic oxides. Sodium oxide reacts with water to form sodium hydroxide.
Answer: (D)

Question 26

Which row identifies a transition element?

▶️ Answer/Explanation
Transition elements are metals that have high melting points and high densities. They also form coloured compounds and often act as catalysts.
Answer: (A)

Question 27

Which statement about Group I or Group VII elements is correct?

A. Group VII elements are monatomic non-metals.
B. Lithium is more reactive with water than caesium.
C. The melting point of Group I metals increases down the group.
D. Potassium bromide reacts with chlorine to produce an orange solution.

▶️ Answer/Explanation
When chlorine reacts with potassium bromide: \(\mathrm{Cl_2 + 2KBr \rightarrow 2KCl + Br_2}\). The bromine produced gives an orange colour in aqueous solution. This is a displacement reaction where the more reactive halogen (chlorine) displaces the less reactive halogen (bromine).
(A) is false — Group VII halogens are diatomic (\(\mathrm{F_2, Cl_2, Br_2, I_2}\)).
(B) is false — reactivity increases down Group I, so caesium is more reactive than lithium.
(C) is false — melting points decrease down Group I.
Answer: (D)

Question 28

Some information about four metals P, Q, R and S is listed.

Metal P does not react with dilute hydrochloric acid.

Metal Q is more reactive than magnesium.

Metal R reacts rapidly with cold water to produce hydrogen.

Metal S reacts with dilute hydrochloric acid to produce hydrogen.

Which row identifies P, Q, R and S?

▶️ Answer/Explanation
P does not react with dilute HCl → P is below hydrogen in the reactivity series (Cu, Ag, Au).
Q is more reactive than Mg → Q must be K, Na, or Ca.
R reacts rapidly with cold water → R must be K, Na, or Ca.
S reacts with dilute HCl to produce H₂ → S must be above hydrogen but not necessarily above Mg (Mg, Al, Zn, Fe).
In option (B): P = Cu (below H, correct), Q = K (more reactive than Mg, correct), R = Ca (reacts with cold water, correct), S = Mg (reacts with dilute HCl producing H₂, correct).
Answer: (B)

Question 29

Cars are fitted with catalytic converters.

Which equation represents a reaction that takes place in a catalytic converter?

A. \(\mathrm{CO_2 + NO_2 \rightarrow CO + NO + O_2}\)
B. \(\mathrm{2CO + 2NO \rightarrow 2CO_2 + N_2}\)
C. \(\mathrm{CO_2 + N_2 \rightarrow C + 2NO}\)
D. \(\mathrm{C + NO_2 \rightarrow CO + NO}\)

▶️ Answer/Explanation
Catalytic converters in cars convert harmful exhaust gases (carbon monoxide, CO, and nitrogen monoxide, NO) into harmless gases (carbon dioxide, CO₂, and nitrogen, N₂). The reaction is: \(2\mathrm{CO + 2NO \rightarrow 2CO_2 + N_2}\).
Answer: (B)

Question 30

Three statements about greenhouse gases and global warming are listed.

  1. A greenhouse gas molecule can absorb and emit thermal energy.
  2. The Earth is a source of thermal energy.
  3. Thermal energy emitted by a greenhouse gas molecule is sent out in all directions.

Which statements are correct?

A. 1, 2 and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only

▶️ Answer/Explanation
All three statements are correct. Greenhouse gas molecules (like CO₂ and CH₄) absorb infrared (thermal) radiation and re-emit it. The Earth absorbs energy from the Sun and re-emits it as thermal energy. When a greenhouse gas molecule emits thermal energy, it is emitted in all directions — some escapes to space, and some is directed back toward Earth, contributing to the greenhouse effect.
Answer: (A)

Question 31

Which type of reaction takes place when methane reacts with chlorine in the presence of ultraviolet light?

A. addition
B. cracking
C. polymerisation
D. substitution

▶️ Answer/Explanation
The reaction of methane with chlorine in UV light is a photochemical substitution reaction: \(\mathrm{CH_4 + Cl_2 \xrightarrow{UV} CH_3Cl + HCl}\). In this reaction, a hydrogen atom in methane is substituted (replaced) by a chlorine atom. UV light provides the activation energy needed to break the Cl−Cl bond.
Answer: (D)

Question 32

Iron is extracted from iron(III) oxide in the blast furnace.

Three steps in the process are listed.

  1. Carbon (coke) is completely oxidised.
  2. Iron(III) oxide is reduced.
  3. Carbon dioxide is reduced to carbon monoxide.

What is the correct order of the steps in the extraction of iron?

A. 1 → 2 → 3
B. 1 → 3 → 2
C. 2 → 1 → 3
D. 3 → 1 → 2

▶️ Answer/Explanation
Step 1: Coke (carbon) is completely oxidised at the bottom of the furnace: \(\mathrm{C + O_2 \rightarrow CO_2}\) (provides heat).
Step 3: Carbon dioxide is reduced to carbon monoxide: \(\mathrm{CO_2 + C \rightarrow 2CO}\).
Step 2: Iron(III) oxide is reduced by carbon monoxide: \(\mathrm{Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2}\).
Correct order: 1 → 3 → 2.
Answer: (B)

Question 33

Three different reactions that occur during the extraction of aluminium from purified bauxite are listed.

  1. \(\mathrm{Al^{3+} + 3e^- \rightarrow Al}\)
  2. \(\mathrm{C + O_2 \rightarrow CO_2}\)
  3. \(\mathrm{2O^{2-} \rightarrow O_2 + 4e^-}\)

Which reactions occur at the anode?

A. 1 and 2
B. 1 only
C. 2 and 3
D. 3 only

▶️ Answer/Explanation
In the extraction of aluminium by electrolysis:
At the anode (+), oxidation occurs. Reaction 3 (\(\mathrm{2O^{2-} \rightarrow O_2 + 4e^-}\)) is the oxidation of oxide ions at the anode. Reaction 2 (\(\mathrm{C + O_2 \rightarrow CO_2}\)) also occurs at the anode as the oxygen produced reacts with the carbon anodes, causing them to be regularly replaced.
Reaction 1 is reduction and occurs at the cathode (−).
Answer: (C)

Question 34

Which statement about aqueous ethanoic acid is correct?

A. It reacts with magnesium to form oxygen gas.
B. It reacts with sodium carbonate to form carbon dioxide gas.
C. It turns red litmus paper blue.
D. It turns methyl orange yellow.

▶️ Answer/Explanation
Ethanoic acid reacts with sodium carbonate to produce carbon dioxide gas: \(\mathrm{2CH_3COOH + Na_2CO_3 \rightarrow 2CH_3COONa + H_2O + CO_2}\).
(A) is false — ethanoic acid reacts with magnesium to form hydrogen gas, not oxygen.
(C) is false — acids turn blue litmus red, not the reverse.
(D) is false — acids turn methyl orange red/pink, not yellow (yellow is for alkalis).
Answer: (B)

Question 35

The diagrams represent four monomers.

The monomers each react in a 1:1 ratio with the dicarboxylic acid shown.

How many of the four monomers shown can react with the dicarboxylic acid to form a polymer?

A. 1
B. 2
C. 3
D. 4

▶️ Answer/Explanation
To form a condensation polymer with a dicarboxylic acid, the monomer must have two functional groups that can react with the −COOH groups. This means the monomer must be a diol (two −OH groups) or a diamine (two −NH₂ groups) to form polyesters or polyamides respectively. Only monomers with two reactive functional groups in a 1:1 ratio can form polymers. Of the four monomers shown, 2 satisfy this requirement.
Answer: (B)

Question 36

Propene undergoes addition reactions with bromine, hydrogen and steam.

Which structures represent a product of these reactions?

A. 1 and 3
B. 1 and 4
C. 2 and 3
D. 3 and 4

▶️ Answer/Explanation
Propene (\(\mathrm{CH_3CH=CH_2}\)) undergoes addition reactions across the C=C double bond:
+ H₂ → propane (\(\mathrm{CH_3CH_2CH_3}\))
+ Br₂ → 1,2-dibromopropane (\(\mathrm{CH_3CHBrCH_2Br}\))
+ H₂O (steam) → mainly propan-2-ol (\(\mathrm{CH_3CH(OH)CH_3}\)) according to Markovnikov’s rule.
Option (D) shows the structures representing these products.
Answer: (D)

Question 37

The structures of four compounds are shown.

Which compounds are members of the same homologous series?

A. 1, 2 and 3
B. 1 and 2 only
C. 1 and 4
D. 2 and 4

▶️ Answer/Explanation
Members of the same homologous series have the same functional group and differ by −CH₂− units. Looking at the structures, compound 2 and compound 4 both contain the alcohol (−OH) functional group and belong to the same homologous series (alcohols). Compound 1 is a carboxylic acid, and compound 3 belongs to a different series.
Answer: (D)

Question 38

Which statement about ethanoic acid is correct?

A. Ethanol is reduced by bacteria to produce ethanoic acid.
B. Ethanoic acid reacts with magnesium to produce a salt of formula \(\mathrm{CH_3COOMg}\).
C. Ethanoic acid and methanol react in the presence of an acid catalyst to produce ethyl methanoate.
D. Ethanol reacts with acidified aqueous potassium manganate(VII) to produce ethanoic acid.

▶️ Answer/Explanation
Ethanol is oxidised to ethanoic acid by acidified potassium manganate(VII): the purple colour of \(\mathrm{KMnO_4}\) changes to colourless. This is an oxidation reaction.
(A) is false — ethanol is oxidised, not reduced.
(B) is false — the correct formula for magnesium ethanoate is \(\mathrm{(CH_3COO)_2Mg}\).
(C) is false — ethanoic acid + methanol produces methyl ethanoate, not ethyl methanoate.
Answer: (D)

Question 39

Substance X contains one cation.

Two tests are completed on aqueous X.

  • test 1: flame test
  • test 2: addition of aqueous sodium hydroxide dropwise and then in excess

Which row shows a possible combination of observations for the tests?

▶️ Answer/Explanation
Copper(II) ions (\(\mathrm{Cu^{2+}}\)) give a blue-green flame in a flame test, and with aqueous sodium hydroxide form a light blue precipitate of copper(II) hydroxide that is insoluble in excess NaOH.
(A) Yellow flame = Na⁺, but Na⁺ gives no precipitate with NaOH.
(C) Light green flame is not characteristic of any common cation; green ppt. soluble in excess indicates Cr³⁺, but chromium gives no distinct flame colour.
(D) Red flame = Li⁺ or Ca²⁺ (orange-red), but red-brown ppt. indicates Fe³⁺, a mismatch.
Answer: (B)

Question 40

A colourless mixture is separated by paper chromatography.

The steps below describe the method. These steps are not in the correct order.

  1. Remove the chromatography paper from the solvent when the solvent front is near the top of the paper.
  2. Place the chromatography paper in the solvent.
  3. Spray the chromatography paper with a locating agent.
  4. Place a spot of the mixture on the pencil line.
  5. Draw a pencil line at the bottom of the chromatography paper.
  6. Draw a pencil line to mark the position of the solvent front.

What is the correct order for these steps?

A. 3 → 5 → 6 → 4 → 2 → 1
B. 5 → 4 → 3 → 2 → 1 → 6
C. 3 → 5 → 4 → 1 → 2 → 6
D. 5 → 4 → 2 → 1 → 6 → 3

▶️ Answer/Explanation
The correct sequence for paper chromatography is:
Step 5: Draw a pencil line at the bottom of the chromatography paper (baseline).
Step 4: Place a spot of the mixture on the pencil line.
Step 2: Place the chromatography paper in the solvent (solvent level below the baseline).
Step 1: Remove the paper when the solvent front is near the top.
Step 6: Draw a pencil line to mark the position of the solvent front immediately.
Step 3: Spray with a locating agent to make colourless spots visible.
Order: 5 → 4 → 2 → 1 → 6 → 3.
Answer: (D)
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