A GCSE CHEMISTRY OCR J248/04 200
PRACTICE MCQS + RATIONALES |
HIGHER TIER | EXAM 2025
Question 1
Which statement correctly describes the effect of increasing temperature
on the rate of a chemical reaction?
A) Particles have less kinetic energy, so fewer collisions occur
B) The activation energy is lowered, so more particles can react
C) Particles move faster and collide more frequently with greater energy
D) The concentration of reactants increases, speeding up the reaction
Increasing temperature gives particles more kinetic energy, causing
them to move faster and collide more frequently AND with energy ≥
activation energy. Activation energy itself is not changed by temperature
(that's the role of a catalyst).
Answer: C
Question 2
In the equilibrium reaction:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = –92 kJ/mol
What happens to the position of equilibrium if the pressure is increased
at constant temperature?
A) It shifts to the left, favouring reactants
B) It shifts to the right, favouring products
C) No change occurs
D) The reaction stops
Increasing pressure favours the side with fewer moles of gas. Left side: 1
+ 3 = 4 moles; Right side: 2 moles. Therefore, equilibrium shifts right to
reduce pressure.
Answer: B
,Question 3
Which test would confirm the presence of sulfate ions (SO₄²⁻) in a
solution?
A) Add dilute HCl, then barium chloride solution → white precipitate
B) Add dilute HNO₃, then silver nitrate solution → white precipitate
C) Add NaOH solution → blue precipitate
D) Add dilute acid → gas that turns limewater cloudy
The standard test for sulfates: acidify with dilute HCl (to remove
interfering ions), then add BaCl₂. A white precipitate of BaSO₄ confirms
sulfate ions. Option B tests for halides; C tests for Cu²⁺; D tests for
carbonates.
Answer: A
Question 4
A student investigates the electrolysis of concentrated aqueous sodium
chloride using inert electrodes. Which product forms at the anode?
A) Sodium metal
B) Hydrogen gas
C) Chlorine gas
D) Oxygen gas
In concentrated NaCl(aq), Cl⁻ ions are preferentially discharged at the
anode over OH⁻ (due to higher concentration), producing chlorine gas:
2Cl⁻ → Cl₂ + 2e⁻. Sodium is not formed in aqueous solution; hydrogen
forms at the cathode.
Answer: C
Question 5
Which of the following is a correct display formula for ethanoic acid?
A) CH₃CH₂OH
B) CH₃COOH
C) HCOOH
D) C₂H₄
,Ethanoic acid (acetic acid) has the molecular formula C₂H₄O₂ and
display formula CH₃COOH, showing the carboxyl functional group (–
COOH). A is ethanol; C is methanoic acid; D is ethene.
Answer: B
Question 6
A sample of iron oxide contains 70% iron by mass. What is its empirical
formula? (Ar: Fe = 56, O = 16)
A) FeO
B) Fe₂O₃
C) Fe₃O₄
D) FeO₂
Assume 100 g sample: 70 g Fe, 30 g O. Moles Fe = 70/56 = 1.25; Moles O
= 30/16 = 1.875. Ratio Fe:O = 1.25:1.875 = 1:1.5 = 2:3 → Fe₂O₃.
Answer: B
Question 7
Which change would increase the yield of sulfur trioxide in the Contact
Process?
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = –196 kJ/mol
A) Increase temperature
B) Decrease pressure
C) Remove SO₃ as it forms
D) Add a catalyst
Removing product (SO₃) shifts equilibrium right (Le Chatelier).
Increasing temperature favours the endothermic reverse reaction (ΔH
negative = exothermic forward). Decreasing pressure favours side with
more moles (left). Catalysts do not affect yield, only rate.
Answer: C
Question 8
Which statement about crude oil fractional distillation is correct?
, A) Fractions with higher boiling points condense near the top of the
column
B) Bitumen has the lowest boiling point of all fractions
C) Hydrocarbons are separated based on differences in melting point
D) Shorter-chain hydrocarbons have weaker intermolecular forces and
lower boiling points
Fractional distillation separates by boiling point. Shorter chains →
weaker London forces → lower boiling points → rise higher before
condensing. Bitumen has the highest boiling point and collects at the
bottom.
Answer: D
Question 9
A student titrates 25.0 cm³ of NaOH solution with 0.100 mol/dm³ HCl.
The mean titre is 22.5 cm³. What is the concentration of the NaOH
solution?
A) 0.090 mol/dm³
B) 0.100 mol/dm³
C) 0.111 mol/dm³
D) 0.225 mol/dm³
Reaction: NaOH + HCl → NaCl + H₂O (1:1 ratio). Moles HCl = 0.100 ×
(22.5/1000) = 0.00225 mol = moles NaOH. [NaOH] = 0.00225 /
(25.0/1000) = 0.090 mol/dm³.
Answer: A
Question 10
Which pollutant is primarily responsible for acid rain?
A) Carbon monoxide
B) Methane
C) Sulfur dioxide
D) Particulate carbon
PRACTICE MCQS + RATIONALES |
HIGHER TIER | EXAM 2025
Question 1
Which statement correctly describes the effect of increasing temperature
on the rate of a chemical reaction?
A) Particles have less kinetic energy, so fewer collisions occur
B) The activation energy is lowered, so more particles can react
C) Particles move faster and collide more frequently with greater energy
D) The concentration of reactants increases, speeding up the reaction
Increasing temperature gives particles more kinetic energy, causing
them to move faster and collide more frequently AND with energy ≥
activation energy. Activation energy itself is not changed by temperature
(that's the role of a catalyst).
Answer: C
Question 2
In the equilibrium reaction:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = –92 kJ/mol
What happens to the position of equilibrium if the pressure is increased
at constant temperature?
A) It shifts to the left, favouring reactants
B) It shifts to the right, favouring products
C) No change occurs
D) The reaction stops
Increasing pressure favours the side with fewer moles of gas. Left side: 1
+ 3 = 4 moles; Right side: 2 moles. Therefore, equilibrium shifts right to
reduce pressure.
Answer: B
,Question 3
Which test would confirm the presence of sulfate ions (SO₄²⁻) in a
solution?
A) Add dilute HCl, then barium chloride solution → white precipitate
B) Add dilute HNO₃, then silver nitrate solution → white precipitate
C) Add NaOH solution → blue precipitate
D) Add dilute acid → gas that turns limewater cloudy
The standard test for sulfates: acidify with dilute HCl (to remove
interfering ions), then add BaCl₂. A white precipitate of BaSO₄ confirms
sulfate ions. Option B tests for halides; C tests for Cu²⁺; D tests for
carbonates.
Answer: A
Question 4
A student investigates the electrolysis of concentrated aqueous sodium
chloride using inert electrodes. Which product forms at the anode?
A) Sodium metal
B) Hydrogen gas
C) Chlorine gas
D) Oxygen gas
In concentrated NaCl(aq), Cl⁻ ions are preferentially discharged at the
anode over OH⁻ (due to higher concentration), producing chlorine gas:
2Cl⁻ → Cl₂ + 2e⁻. Sodium is not formed in aqueous solution; hydrogen
forms at the cathode.
Answer: C
Question 5
Which of the following is a correct display formula for ethanoic acid?
A) CH₃CH₂OH
B) CH₃COOH
C) HCOOH
D) C₂H₄
,Ethanoic acid (acetic acid) has the molecular formula C₂H₄O₂ and
display formula CH₃COOH, showing the carboxyl functional group (–
COOH). A is ethanol; C is methanoic acid; D is ethene.
Answer: B
Question 6
A sample of iron oxide contains 70% iron by mass. What is its empirical
formula? (Ar: Fe = 56, O = 16)
A) FeO
B) Fe₂O₃
C) Fe₃O₄
D) FeO₂
Assume 100 g sample: 70 g Fe, 30 g O. Moles Fe = 70/56 = 1.25; Moles O
= 30/16 = 1.875. Ratio Fe:O = 1.25:1.875 = 1:1.5 = 2:3 → Fe₂O₃.
Answer: B
Question 7
Which change would increase the yield of sulfur trioxide in the Contact
Process?
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = –196 kJ/mol
A) Increase temperature
B) Decrease pressure
C) Remove SO₃ as it forms
D) Add a catalyst
Removing product (SO₃) shifts equilibrium right (Le Chatelier).
Increasing temperature favours the endothermic reverse reaction (ΔH
negative = exothermic forward). Decreasing pressure favours side with
more moles (left). Catalysts do not affect yield, only rate.
Answer: C
Question 8
Which statement about crude oil fractional distillation is correct?
, A) Fractions with higher boiling points condense near the top of the
column
B) Bitumen has the lowest boiling point of all fractions
C) Hydrocarbons are separated based on differences in melting point
D) Shorter-chain hydrocarbons have weaker intermolecular forces and
lower boiling points
Fractional distillation separates by boiling point. Shorter chains →
weaker London forces → lower boiling points → rise higher before
condensing. Bitumen has the highest boiling point and collects at the
bottom.
Answer: D
Question 9
A student titrates 25.0 cm³ of NaOH solution with 0.100 mol/dm³ HCl.
The mean titre is 22.5 cm³. What is the concentration of the NaOH
solution?
A) 0.090 mol/dm³
B) 0.100 mol/dm³
C) 0.111 mol/dm³
D) 0.225 mol/dm³
Reaction: NaOH + HCl → NaCl + H₂O (1:1 ratio). Moles HCl = 0.100 ×
(22.5/1000) = 0.00225 mol = moles NaOH. [NaOH] = 0.00225 /
(25.0/1000) = 0.090 mol/dm³.
Answer: A
Question 10
Which pollutant is primarily responsible for acid rain?
A) Carbon monoxide
B) Methane
C) Sulfur dioxide
D) Particulate carbon
