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OCR Chemistry
A-LEVEL
Questions That Repeat Frequently
and How to Answer Them
O
N
C H
H
O
10+ 60+ 100% A*
Topic Areas Exam Questions Model Answers Target Grade
Master Every Exam Topic · Build Exam Confidence · Achieve Top Grades
Covers ALL major OCR A-Level Chemistry exam themes
, ■ Table of Contents
Chapter 1 Atomic Structure & Electronic Configuration p. 3
Chapter 2 Bonding, Structure & Properties of Matter p. 5
Chapter 3 Amount of Substance & Calculations p. 7
Chapter 4 Acids, Bases & Redox Reactions p. 9
p.
Chapter 5 Energetics & Enthalpy Changes 11
p.
Chapter 6 Kinetics & Reaction Rates 13
p.
Chapter 7 Equilibria & Le Chatelier's Principle 15
p.
Chapter 8 Organic Chemistry: Hydrocarbons 17
p.
Chapter 9 Organic Chemistry: Functional Groups 19
p.
Chapter 10 Electrochemistry & Electrolysis 21
p.
Chapter 11 Transition Metals & Complex Ions 23
p.
Chapter 12 Spectroscopy & Analytical Techniques 25
Quick-Reference Formula Sheet
Last-Minute Checklist
OCR Chemistry A-Level Questions That Repeat Frequently and How to Answer Them
, Chapter 1 ■ Atomic Structure & Electronic
Configuration
Questions about atomic structure appear in almost every OCR A-Level Chemistry paper. You need to know
how atoms are built, how electrons are arranged, and what mass spectrometry shows us. These questions
can be short one-mark tasks or six-mark extended responses.
Key Particles at a Glance
Sym Relative
Particle Relative Mass Location
bol Charge
Proton p 1 +1 Nucleus
Neutron n 1 0 Nucleus
Electron e 1/1836 −1 Shells/orbitals
Q1.
Explain what is meant by the term 'isotopes' and give one example.
■ Model Answer
Isotopes are atoms of the same element that have the same number of protons but different numbers of
neutrons. This gives them the same atomic number but different mass numbers. Example: Carbon-12 (12C)
and Carbon-14 (14C) — both have 6 protons, but 12C has 6 neutrons and 14C has 8 neutrons.
Q2.
Write the full electronic configuration of a Fe2+ ion.
■ Model Answer
Iron (Fe) has atomic number 26. Its neutral configuration is: 1s2 2s2 2p6 3s2 3p6 3d6 4s2. Fe2+ loses 2
electrons from the 4s sub-shell first: 1s2 2s2 2p6 3s2 3p6 3d6.
■ Exam Tip
Always remove electrons from the highest principal quantum number first when forming positive ions. For
transition metals, 4s empties before 3d — this is a very common mistake in exams.
Q3.
A mass spectrum of chlorine shows two peaks. Explain what information these peaks give and how you
would calculate the relative atomic mass.
■ Model Answer
The two peaks represent the two isotopes of chlorine: 35Cl (about 75% abundance) and 37Cl (about 25%
abundance). The x-axis gives the mass-to-charge ratio (m/z) and the y-axis gives relative abundance.
Relative atomic mass = Σ (mass × % abundance) ÷ 100 = (35 × 75 + 37 × 25) ÷ 100 = 35.5.
1
OCR Chemistry A-Level Questions That Repeat Frequently and How to Answer Them
OCR Chemistry
A-LEVEL
Questions That Repeat Frequently
and How to Answer Them
O
N
C H
H
O
10+ 60+ 100% A*
Topic Areas Exam Questions Model Answers Target Grade
Master Every Exam Topic · Build Exam Confidence · Achieve Top Grades
Covers ALL major OCR A-Level Chemistry exam themes
, ■ Table of Contents
Chapter 1 Atomic Structure & Electronic Configuration p. 3
Chapter 2 Bonding, Structure & Properties of Matter p. 5
Chapter 3 Amount of Substance & Calculations p. 7
Chapter 4 Acids, Bases & Redox Reactions p. 9
p.
Chapter 5 Energetics & Enthalpy Changes 11
p.
Chapter 6 Kinetics & Reaction Rates 13
p.
Chapter 7 Equilibria & Le Chatelier's Principle 15
p.
Chapter 8 Organic Chemistry: Hydrocarbons 17
p.
Chapter 9 Organic Chemistry: Functional Groups 19
p.
Chapter 10 Electrochemistry & Electrolysis 21
p.
Chapter 11 Transition Metals & Complex Ions 23
p.
Chapter 12 Spectroscopy & Analytical Techniques 25
Quick-Reference Formula Sheet
Last-Minute Checklist
OCR Chemistry A-Level Questions That Repeat Frequently and How to Answer Them
, Chapter 1 ■ Atomic Structure & Electronic
Configuration
Questions about atomic structure appear in almost every OCR A-Level Chemistry paper. You need to know
how atoms are built, how electrons are arranged, and what mass spectrometry shows us. These questions
can be short one-mark tasks or six-mark extended responses.
Key Particles at a Glance
Sym Relative
Particle Relative Mass Location
bol Charge
Proton p 1 +1 Nucleus
Neutron n 1 0 Nucleus
Electron e 1/1836 −1 Shells/orbitals
Q1.
Explain what is meant by the term 'isotopes' and give one example.
■ Model Answer
Isotopes are atoms of the same element that have the same number of protons but different numbers of
neutrons. This gives them the same atomic number but different mass numbers. Example: Carbon-12 (12C)
and Carbon-14 (14C) — both have 6 protons, but 12C has 6 neutrons and 14C has 8 neutrons.
Q2.
Write the full electronic configuration of a Fe2+ ion.
■ Model Answer
Iron (Fe) has atomic number 26. Its neutral configuration is: 1s2 2s2 2p6 3s2 3p6 3d6 4s2. Fe2+ loses 2
electrons from the 4s sub-shell first: 1s2 2s2 2p6 3s2 3p6 3d6.
■ Exam Tip
Always remove electrons from the highest principal quantum number first when forming positive ions. For
transition metals, 4s empties before 3d — this is a very common mistake in exams.
Q3.
A mass spectrum of chlorine shows two peaks. Explain what information these peaks give and how you
would calculate the relative atomic mass.
■ Model Answer
The two peaks represent the two isotopes of chlorine: 35Cl (about 75% abundance) and 37Cl (about 25%
abundance). The x-axis gives the mass-to-charge ratio (m/z) and the y-axis gives relative abundance.
Relative atomic mass = Σ (mass × % abundance) ÷ 100 = (35 × 75 + 37 × 25) ÷ 100 = 35.5.
1
OCR Chemistry A-Level Questions That Repeat Frequently and How to Answer Them
