A-Level Chemistry 2 — Questions and Answers
Question 1: What is the pH of a 0.01 mol/dm³ solution of hydrochloric acid?
- 1
- 2 (Correct answer)
- 3
- 4
Correct answer: 2
HCl is a strong acid that fully dissociates: [H⁺] = 0.01 = 10⁻² mol/dm³. pH = -log₁₀[H⁺] = -log₁₀(10⁻²) = 2.
Question 2: What is the test for an aldehyde using Tollens' reagent?
- A green precipitate forms
- A silver mirror forms on the test tube walls (Correct answer)
- A blue solution turns colourless
- Bubbles of gas are produced
Correct answer: A silver mirror forms on the test tube walls
Tollens' reagent (ammoniacal silver nitrate) is reduced by aldehydes to form metallic silver, which deposits as a mirror-like coating on the test tube. This is the 'silver mirror test'.
Question 3: What is the molecular geometry of SF₆ according to VSEPR theory?
- Tetrahedral
- Trigonal bipyramidal
- Octahedral (Correct answer)
- Square planar
Correct answer: Octahedral
SF₆ has six bonding pairs around the central sulphur atom and no lone pairs, giving an octahedral geometry with 90° bond angles.
Question 4: In electrochemistry, what happens at the cathode during electrolysis?
- Oxidation occurs
- Reduction occurs — cations gain electrons (Correct answer)
- No reaction occurs
- Anions lose electrons
Correct answer: Reduction occurs — cations gain electrons
At the cathode (negative electrode), cations are attracted and gain electrons (reduction). Remember: 'CATions go to the CAThode' and 'Reduction at the Cathode'.
Question 5: What is a peptide bond in the context of A-Level organic chemistry?
- A bond between two sugars
- A covalent bond formed between the amino group of one amino acid and the carboxyl group of another through a condensation reaction (Correct answer)
- A hydrogen bond in proteins
- An ionic bond in amino acids
Correct answer: A covalent bond formed between the amino group of one amino acid and the carboxyl group of another through a condensation reaction
A peptide bond (-CO-NH-) forms through a condensation reaction between the -NH₂ group of one amino acid and the -COOH group of another, releasing a molecule of water.
Question 6: What is the first ionisation energy trend across Period 3 of the Periodic Table?
- It decreases uniformly
- It generally increases across the period with dips at Al and S due to electron configuration effects (Correct answer)
- It stays constant
- It decreases then increases
Correct answer: It generally increases across the period with dips at Al and S due to electron configuration effects
First ionisation energy generally increases across Period 3 due to increasing nuclear charge. However, dips occur at Al (electron enters 3p, easier to remove) and S (paired electron in 3p experiences repulsion).
A-Level Chemistry 2
What is the pH of a 0.01 mol/dm³ solution of hydrochloric acid?