A-Level Chemistry Fundamentals — Questions and Answers
Question 1: What is the shape and bond angle of a methane (CH₄) molecule?
- Tetrahedral, 109.5° (Correct answer)
- Trigonal planar, 120°
- Linear, 180°
- Pyramidal, 107°
Correct answer: Tetrahedral, 109.5°
Methane has four bonding pairs of electrons around the central carbon atom with no lone pairs, giving a tetrahedral shape with bond angles of 109.5° as predicted by VSEPR theory.
Question 2: Which of the following best describes an ionic bond?
- Electrostatic attraction between oppositely charged ions formed by electron transfer (Correct answer)
- A shared pair of electrons between two non-metal atoms
- Delocalised electrons in a sea surrounding positive metal ions
- A weak intermolecular force between polar molecules
Correct answer: Electrostatic attraction between oppositely charged ions formed by electron transfer
Ionic bonding involves the transfer of electrons from a metal to a non-metal, creating positively and negatively charged ions held together by strong electrostatic attraction in a giant ionic lattice.
Question 3: In a titration, 25.0 cm³ of 0.100 mol dm⁻³ NaOH is exactly neutralised by HCl. If 20.0 cm³ of HCl was used, what is its concentration?
- 0.125 mol dm⁻³ (Correct answer)
- 0.100 mol dm⁻³
- 0.0800 mol dm⁻³
- 0.200 mol dm⁻³
Correct answer: 0.125 mol dm⁻³
Moles of NaOH = 0.025 × 0.100 = 0.0025 mol. NaOH:HCl ratio is 1:1, so moles of HCl = 0.0025. Concentration = 0.0025 / 0.020 = 0.125 mol dm⁻³.
Question 4: What is the oxidation state of manganese in the permanganate ion MnO₄⁻?
- +7 (Correct answer)
- +4
- +5
- +6
Correct answer: +7
Each oxygen is -2, giving 4 × (-2) = -8. The overall charge is -1. So Mn + (-8) = -1, therefore Mn = +7. Permanganate is a powerful oxidising agent due to this high oxidation state.
Question 5: Which of the following molecules exhibits hydrogen bonding?
- HF (Correct answer)
- CH₄
- H₂S
- PH₃
Correct answer: HF
Hydrogen bonding requires hydrogen bonded to a highly electronegative atom (F, O, or N). HF fits this criterion as fluorine is the most electronegative element. H₂S and PH₃ only have weaker van der Waals forces as S and P are not sufficiently electronegative.
Question 6: What is the empirical formula of a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?
- CH₂O (Correct answer)
- C₂H₄O₂
- CHO
- C₃H₆O₃
Correct answer: CH₂O
Dividing by atomic masses: C = 40.0/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33. Ratio = 1:2:1, giving empirical formula CH₂O.
A-Level Chemistry Fundamentals
What is the shape and bond angle of a methane (CH₄) molecule?