Edexcel International AS & A Level Chemistry: every topic, by paper

Define the Avogadro constant.

The number of particles in one mole of a substance: 6.02 × 10²³ mol⁻¹.

Define relative atomic mass (Ar).

The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.

How do you calculate amount in moles from mass?

n = m ÷ M, where m is mass in g and M is molar mass in g mol⁻¹.

Give the relative mass and charge of a proton, neutron and electron.

Proton: 1, +1. Neutron: 1, 0. Electron: 1/1836, −1.

What are isotopes?

Atoms of the same element with the same number of protons but different numbers of neutrons.

How do protons, neutrons and electrons behave in an electric field?

Protons are deflected towards the negative plate, electrons (more strongly) towards the positive plate; neutrons are not deflected.

What is periodicity?

A repeating pattern of physical or chemical properties across periods.

Why does atomic radius decrease across Period 3?

Nuclear charge increases while electrons are added to the same shell with similar shielding.

Explain the trend in melting point from Na to Al.

Metallic bonding strengthens as ion charge increases and more electrons are delocalised, and ions get smaller.

What is an ionic bond?

Electrostatic attraction between oppositely charged ions.

What is a covalent bond?

A shared pair of electrons attracted to the nuclei of both atoms.

What is a dative (coordinate) bond?

A covalent bond in which both shared electrons come from the same atom, e.g. in NH₄⁺.

What is a homologous series?

A family of compounds with the same functional group and general formula, differing by CH₂.

What is a functional group?

The atom or group of atoms responsible for a compound's characteristic reactions.

Distinguish molecular, structural, displayed and skeletal formulae.

Molecular: number of each atom. Structural: arrangement without all bonds (e.g. CH₃CH₂OH). Displayed: all bonds shown. Skeletal: carbon chain as lines, H on C omitted.

What is the general formula of the alkanes?

CₙH₂ₙ₊₂.

Why are alkanes unreactive?

C–C and C–H bonds are strong and non-polar.

Write equations for complete and incomplete combustion of methane.

Complete: CH₄ + 2O₂ → CO₂ + 2H₂O. Incomplete: 2CH₄ + 3O₂ → 2CO + 4H₂O.

Distinguish exothermic and endothermic reactions.

Exothermic reactions release heat (ΔH negative); endothermic reactions absorb heat (ΔH positive).

Give the standard conditions for enthalpy changes.

100 kPa, 298 K, solutions at 1 mol dm⁻³, substances in their standard states.

Define standard enthalpy change of formation.

The enthalpy change when one mole of a compound forms from its elements in their standard states under standard conditions.

Define oxidation and reduction in terms of electrons.

Oxidation is loss of electrons; reduction is gain of electrons.

What is the oxidation number of an uncombined element?

Zero.

Give the oxidation number of oxygen in most compounds and two exceptions.

−2; −1 in peroxides and +2 in OF₂.

Why do Group 2 elements form 2+ ions?

They have two outer electrons, which they lose.

How does the atomic radius change down Group 2?

It increases, as more electron shells are added.

Why does the first ionisation energy decrease down Group 2?

Outer electrons are further from the nucleus and more shielded, despite greater nuclear charge.

Give the colours and states of chlorine, bromine and iodine at room temperature.

Chlorine: pale green gas. Bromine: red-brown liquid. Iodine: grey-black solid (purple vapour).

Why do boiling points increase down Group 17?

Molecules have more electrons, so London forces are stronger.

Why does oxidising power decrease down Group 17?

Atoms are larger and more shielded, so they gain an electron less readily.

Give four factors that affect the rate of reaction.

Concentration (or pressure), temperature, surface area and catalysts.

Explain why increasing concentration increases rate.

More particles per unit volume, so more frequent collisions and more successful collisions per second.

What does a Boltzmann distribution show?

The number of molecules with each kinetic energy; the area under the curve is the total number of molecules.

What is a dynamic equilibrium?

Forward and reverse reactions occur at the same rate, so concentrations stay constant, in a closed system.

State Le Chatelier's principle.

If a condition of a system in equilibrium changes, the position of equilibrium shifts to oppose the change.

What happens to an exothermic equilibrium when temperature rises?

It shifts in the endothermic (backward) direction and Kc decreases.

Give the general formula of a halogenoalkane.

CₙH₂ₙ₊₁X, where X is a halogen.

Why is the C–X bond polar?

The halogen is more electronegative than carbon, making carbon δ+.

Classify CH₃CH₂CH₂Br, CH₃CHBrCH₃ and (CH₃)₃CBr.

Primary, secondary and tertiary.

What is the functional group of an alcohol?

The hydroxyl group, –OH.

Why do alcohols have higher boiling points than alkanes of similar Mr?

They form hydrogen bonds between molecules.

Why are short-chain alcohols soluble in water?

The –OH group forms hydrogen bonds with water.

What does infrared spectroscopy identify?

Functional groups, from the absorption of IR radiation by bonds vibrating.

Where does an O–H bond absorb in an alcohol and a carboxylic acid?

Alcohol: broad peak about 3200–3600 cm⁻¹. Carboxylic acid: very broad peak about 2500–3300 cm⁻¹.

Where does a C=O bond absorb in IR?

Sharp, strong peak about 1680–1750 cm⁻¹.

Give four factors that affect the rate of reaction.

Concentration (or pressure), temperature, surface area and catalysts.

Explain why increasing concentration increases rate.

More particles per unit volume, so more frequent collisions and more successful collisions per second.

What does a Boltzmann distribution show?

The number of molecules with each kinetic energy; the area under the curve is the total number of molecules.

What is a dynamic equilibrium?

Forward and reverse reactions occur at the same rate, so concentrations stay constant, in a closed system.

State Le Chatelier's principle.

If a condition of a system in equilibrium changes, the position of equilibrium shifts to oppose the change.

What happens to an exothermic equilibrium when temperature rises?

It shifts in the endothermic (backward) direction and Kc decreases.

Define lattice energy (formation convention).

The enthalpy change when one mole of an ionic solid forms from its gaseous ions.

Define enthalpy change of atomisation.

The enthalpy change when one mole of gaseous atoms forms from an element in its standard state.

Define first electron affinity.

The enthalpy change when one mole of gaseous atoms each gain an electron to form one mole of gaseous 1− ions.

Define a Brønsted–Lowry acid and base.

An acid is a proton donor; a base is a proton acceptor.

What are conjugate acid–base pairs?

Species differing by one proton, e.g. CH₃COOH and CH₃COO⁻.

Define pH.

pH = −log₁₀[H⁺].

What is the functional group of aldehydes and ketones?

The carbonyl group, C=O; at the end of the chain in aldehydes, within the chain in ketones.

How do Tollens' reagent and Fehling's solution distinguish aldehydes from ketones?

Aldehydes give a silver mirror with Tollens' and a brick-red precipitate with Fehling's; ketones give no change.

What does 2,4-DNPH test for?

Carbonyl groups: an orange precipitate forms with aldehydes and ketones.

What does infrared spectroscopy identify?

Functional groups, from the absorption of IR radiation by bonds vibrating.

Where does an O–H bond absorb in an alcohol and a carboxylic acid?

Alcohol: broad peak about 3200–3600 cm⁻¹. Carboxylic acid: very broad peak about 2500–3300 cm⁻¹.

Where does a C=O bond absorb in IR?

Sharp, strong peak about 1680–1750 cm⁻¹.

What is a half-cell?

An element in contact with its ions, or two ions of an element in solution with an inert electrode.

Define standard electrode potential.

The e.m.f. of a half-cell compared with the standard hydrogen electrode under standard conditions.

Describe the standard hydrogen electrode.

H₂ gas at 100 kPa bubbled over a platinum electrode in 1.00 mol dm⁻³ H⁺ at 298 K.

Define a transition element.

A d-block element that forms one or more stable ions with an incomplete d subshell.

Why are scandium and zinc not transition elements?

Sc³⁺ has an empty d subshell and Zn²⁺ a full one.

Give four properties of transition elements.

Variable oxidation states, coloured compounds, complex ion formation and catalytic activity.

What is the molecular formula of benzene?

C₆H₆.

Describe the bonding in benzene.

A planar ring of six carbons with σ bonds; p orbitals overlap to form a delocalised π system above and below the ring.

Give evidence against the Kekulé structure of benzene.

All C–C bond lengths are equal; benzene resists addition; its enthalpy of hydrogenation is less exothermic than expected.

What is the functional group of a primary amine?

–NH₂.

Why are amines bases?

The lone pair on nitrogen accepts a proton.

Why are aliphatic amines stronger bases than ammonia?

Alkyl groups push electron density onto nitrogen, making the lone pair more available.