OCR A-Level Chemistry A sample questions and answers (H432)
Guide overview All 17 sections Sample questions Papers and weighting Look inside Questions and answers
51 sample questions and answers
Taken from every section of OCR A-Level Chemistry A, specification H432. The full guide has 1,913.
Component 01, Component 02, Component 03
Foundations in Chemistry
284 questions in the guide, across 23 subtopics. More from this section
-
Atomic structure, isotopes and counting sub-atomic particles
Define the mass number of an atom.
Show the answer
The total number of protons and neutrons in the nucleus. -
Predicting ionic charges and the common ions
State the formula of the hydroxide ion.
Show the answer
OH⁻ -
Empirical and molecular formulae, and hydrated salts
If dividing molar ratios by the smallest value gives non-whole numbers, what should you do?
Show the answer
Multiply all values to obtain whole numbers.
Component 01, Component 02, Component 03
Bonding and Structure
117 questions in the guide, across 10 subtopics. More from this section
-
Ionic bonding and the properties of ionic compounds
Why do ionic compounds have high melting and boiling points?
Show the answer
A large amount of energy is required to overcome the strong electrostatic attractions between ions throughout the lattice -
Covalent and coordinate bonding
Why are dots and crosses used as different symbols in dot-and-cross diagrams?
Show the answer
To distinguish which atom each electron originally came from in the molecule. -
Lone pairs, bonding pairs and average bond enthalpy
What does a larger average bond enthalpy value indicate about a covalent bond?
Show the answer
It indicates a stronger covalent bond.
Component 01, Component 03
Periodic Table and Energy
177 questions in the guide, across 15 subtopics. More from this section
-
Periodicity and the electron configurations of periods 2 and 3
State the electron configuration of carbon.
Show the answer
1s² 2s² 2p² -
The blocks, and first and successive ionisation energies
Explain the small decrease in first ionisation energy between magnesium and aluminium.
Show the answer
Aluminium's outer electron is in a 3p subshell, which is higher in energy than magnesium's 3s subshell, making it easier to remove. -
Group 2 reactions with oxygen, water and acids
In terms of electron transfer, what type of change occurs when a Group 2 metal forms a 2+ ion?
Show the answer
Oxidation, because the metal loses electrons
Component 01, Component 03
Enthalpy Changes
89 questions in the guide, across 8 subtopics. More from this section
-
Exothermic and endothermic reactions and enthalpy profiles
A reaction absorbs energy from its surroundings. What sign does its ΔH have?
Show the answer
Positive (ΔH > 0), indicating an endothermic reaction. -
Standard conditions and the standard enthalpy changes
Define the standard enthalpy change of formation (ΔfH⦵).
Show the answer
The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions. -
Bond enthalpies, q = mcΔT and calorimetry
Explain why a reaction is exothermic overall in terms of bond energies.
Show the answer
A reaction is exothermic overall when the energy released in forming new bonds is greater than the energy required to break the bonds in the reactants.
Component 01, Component 03
Chemical Equilibrium
36 questions in the guide, across 4 subtopics. More from this section
-
Dynamic equilibrium and le Chatelier's principle
Why must a system be closed for dynamic equilibrium to be established?
Show the answer
No substances can enter or leave a closed system, so the reactants and products remain within the system to maintain equilibrium. -
Dynamic equilibrium and le Chatelier's principle
How does removing a product from an equilibrium mixture affect the position of equilibrium?
Show the answer
The equilibrium position shifts towards the products to replace the removed product. -
Pressure, catalysts and investigating a shift in equilibrium
For the equilibrium H₂(g) + I₂(g) ⇌ 2HI(g), what effect does changing pressure have on the position of equilibrium?
Show the answer
No effect, because both sides have equal moles of gas (2 moles on each side).
Component 02, Component 03
Basic Concepts of Organic Chemistry
82 questions in the guide, across 7 subtopics. More from this section
-
IUPAC nomenclature and the alkyl groups
What principle determines which end of the carbon chain to start numbering from?
Show the answer
The chain is numbered so that substituents receive the lowest possible locant numbers. -
IUPAC nomenclature and the alkyl groups
What are the names of the alkyl groups derived from the first five alkanes?
Show the answer
Methyl, ethyl, propyl, butyl, and pentyl. -
General, structural, displayed and skeletal formulae
In a skeletal formula, what does each vertex and line end represent?
Show the answer
Each vertex and line end represents a carbon atom.
Component 02, Component 03
Core Organic Chemistry
116 questions in the guide, across 9 subtopics. More from this section
-
Alkanes: bonding, shape and boiling points
What is the shape around each carbon atom in an alkane?
Show the answer
Tetrahedral. -
Combustion of alkanes and their reaction with halogens
Why is carbon monoxide produced from incomplete combustion dangerous to humans?
Show the answer
It is a toxic gas that binds to haemoglobin, preventing oxygen transport in the blood. -
The radical substitution mechanism and its limitations
Why does the combination of two radicals terminate the chain reaction?
Show the answer
Because no new radicals are produced, so the chain cannot continue.
Component 02, Component 03
Alkenes
86 questions in the guide, across 6 subtopics. More from this section
-
Alkenes: the double bond, sigma and pi bonding, and shape
Why is there no free rotation about the carbon-carbon double bond in alkenes?
Show the answer
Rotation would break the sideways overlap of the p-orbitals that form the pi bond. -
Alkenes: the double bond, sigma and pi bonding, and shape
Why are alkenes much more reactive than alkanes?
Show the answer
The π-bond in the C=C bond has a relatively low bond enthalpy, so it breaks easily, whereas alkanes contain only strong σ-bonds. -
E/Z and cis-trans isomerism in alkenes
What system of rules is used to assign E and Z labels to stereoisomers?
Show the answer
The Cahn-Ingold-Prelog (CIP) priority rules.
Component 02, Component 03
Organic Synthesis
52 questions in the guide, across 5 subtopics. More from this section
-
Reflux, distillation and separating an organic layer
What is the purpose of heating under reflux using Quickfit apparatus?
Show the answer
To heat a reaction mixture for an extended period without losing volatile reactants or products, as vapours condense and return to the flask. -
Reflux, distillation and separating an organic layer
When using a separating funnel, how do you determine which layer is the organic layer?
Show the answer
By comparing densities; the organic layer floats on top if less dense than water, or sinks to the bottom if more dense than water. -
Purifying an organic solid and testing its purity
What two techniques are combined to purify an organic solid?
Show the answer
Recrystallisation and filtration under reduced pressure.
Component 01, Component 03
How Fast?
107 questions in the guide, across 10 subtopics. More from this section
-
Rate equations, order and the rate constant
What is the role of the rate constant k in a rate equation?
Show the answer
The rate constant k is the proportionality constant that relates the rate to the concentrations of reactants raised to their respective orders. -
Deducing orders and finding the units of k
Why might the orders in a rate equation differ from the stoichiometric coefficients in the balanced equation?
Show the answer
Because orders depend on the reaction mechanism, not the overall stoichiometry, and can only be determined experimentally. -
What the rate equation reveals about the mechanism
Why might a reactant shown in the overall equation not appear in the rate equation?
Show the answer
Because that reactant only participates in faster subsequent steps after the rate-determining step.
Component 01, Component 03
Physical Chemistry and Transition Elements
101 questions in the guide, across 7 subtopics. More from this section
-
Mole fraction, partial pressure and ICE tables
State the relationship between partial pressure, mole fraction, and total pressure.
Show the answer
Partial pressure equals mole fraction multiplied by total pressure: pₐ = xₐ × P_total. -
Mole fraction, partial pressure and ICE tables
How are equilibrium moles determined in an ICE table calculation?
Show the answer
Calculate equilibrium moles by adding the initial amounts and the changes for each species. -
Kc and Kp expressions, their units and calculations
Why are solids and pure liquids omitted from Kc and Kp expressions in heterogeneous equilibria?
Show the answer
Because their concentrations are constant and do not affect the equilibrium expression.
Component 01, Component 03
Acids, Bases and Buffers
120 questions in the guide, across 9 subtopics. More from this section
-
Brønsted-Lowry acids and bases and their reactions
When a base accepts a proton, what is formed?
Show the answer
Its conjugate acid. -
Ka, pKa, pH and the ionic product of water
State the relationship between pKₐ and Kₐ.
Show the answer
pKₐ = −log Kₐ -
Calculating the pH of strong acids, strong bases and weak acids
State the formula used to calculate pH of a strong base using Kw.
Show the answer
pH = −log(Kw / [OH⁻])
Component 01, Component 03
Redox and Electrode Potentials
78 questions in the guide, across 6 subtopics. More from this section
-
Oxidising and reducing agents, and balancing half-equations
Why does a reducing agent become oxidised during a reaction?
Show the answer
Because it loses electrons to another species, and losing electrons is the definition of oxidation. -
Oxidising and reducing agents, and balancing half-equations
In balancing a half-equation, how do you balance atoms other than oxygen and hydrogen?
Show the answer
Add coefficients to ensure the number of each type of atom (excluding O and H) is equal on both sides. -
Combining half-equations and using oxidation numbers
How can you identify which species is oxidised in a redox reaction using oxidation numbers?
Show the answer
The species whose oxidation number increases is the one that has been oxidised.
Component 01, Component 03
Transition Elements
131 questions in the guide, across 10 subtopics. More from this section
-
Ligands, complex ions and coordination number
Is water a monodentate or bidentate ligand?
Show the answer
Monodentate. -
Electron configurations from Sc to Zn, and which are transition elements
What is the electron configuration of an Fe²⁺ ion?
Show the answer
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶, or [Ar] 3d⁶: both 4s electrons are lost before any 3d electron. -
Variable oxidation states, coloured ions and catalysis
Give the colours of three transition metal ions in aqueous solution.
Show the answer
Cu²⁺(aq) is pale blue, Fe²⁺(aq) is pale green and MnO₄⁻(aq) is purple.
Component 02, Component 03
Aromatic Compounds
65 questions in the guide, across 6 subtopics. More from this section
-
The delocalised model of benzene and the evidence for it
What type of system is formed when the p-orbitals in benzene overlap, and how is the electron density distributed?
Show the answer
A delocalised π-system is formed, with electron density distributed equally around the ring. -
The delocalised model of benzene and the evidence for it
How does the enthalpy change of hydrogenation of benzene provide evidence for delocalisation?
Show the answer
The enthalpy change of hydrogenation is less exothermic than expected for a structure with three isolated double bonds. -
Nitration, halogenation and Friedel-Crafts reactions of benzene
What reagents are used in a Friedel-Crafts reaction?
Show the answer
A haloalkane or acyl chloride in the presence of a halogen carrier.
Component 02, Component 03
Organic Chemistry and Analysis
184 questions in the guide, across 17 subtopics. More from this section
-
Oxidation and reduction of carbonyls, and the addition of HCN
Which ion acts as the oxidising agent when aldehydes are oxidised in acidic solution?
Show the answer
The dichromate ion, Cr₂O₇²⁻ -
2,4-DNPH and Tollens' reagent
Why do different carbonyl compounds form derivatives with 2,4-DNPH that can be distinguished from each other?
Show the answer
Each derivative has a characteristic melting point -
Esterification and the hydrolysis of esters
What are the products when an acid anhydride reacts with an alcohol?
Show the answer
An ester and a carboxylic acid.
Component 02, Component 03
Spectroscopy
88 questions in the guide, across 8 subtopics. More from this section
-
Carbon-13 and proton NMR: peaks, chemical shift and integration
What does 'proton decoupled' mean in the context of carbon-13 NMR spectra?
Show the answer
Each carbon environment appears as a single peak rather than being split by coupling to attached protons. -
Spin-spin splitting and predicting a spectrum
A triplet splitting pattern indicates how many adjacent non-equivalent protons?
Show the answer
Two adjacent non-equivalent protons. -
TMS, deuterated solvents and the D₂O shake
Why do the protons and carbons in TMS appear at a chemical shift defined as zero?
Show the answer
Because they are in highly shielded environments, producing signals at higher field than most organic compounds.
OCR A-Level Chemistry A Active Recall Guide
The other 1,862 questions, with the answers printed after each section.