GCE Advanced Level (A-Levels) Chemistry Syllabus

Give the Gibbs free energy equation and the condition for a feasible (spontaneous) reaction.

$\Delta G = \Delta H - T\Delta S$; the reaction is feasible when $\Delta G \leq 0$.

What is the lattice enthalpy of formation, and is it exothermic or endothermic?

The enthalpy change when one mole of an ionic solid is formed from its gaseous ions; it is exothermic (negative).

Define activation energy.

The minimum energy that colliding particles must have for a reaction to occur.

How does a catalyst increase reaction rate?

It provides an alternative reaction pathway with a lower activation energy, so a greater proportion of molecules have sufficient energy to react.

For a reaction $\text{rate} = k[\ce{A}]^2[\ce{B}]$, state the overall order and the units of $k$.

Overall order $= 3$; units of $k$ are $\text{mol}^{-2}\,\text{dm}^{6}\,\text{s}^{-1}$.

What is the rate-determining step?

The slowest step in a multi-step reaction mechanism, which governs the overall rate; only species up to and including this step appear in the rate equation.

State Le Chatelier's principle.

When a system at equilibrium is subjected to a change in conditions, the position of equilibrium shifts to oppose (minimise) that change.

Write the equilibrium constant expression $K_c$ for $\ce{N2(g) + 3H2(g) <=> 2NH3(g)}$.

$K_c = \dfrac{[\ce{NH3}]^2}{[\ce{N2}][\ce{H2}]^3}$.

For an exothermic forward reaction, how does increasing temperature affect $K_c$?

$K_c$ decreases, because the equilibrium shifts in the endothermic (reverse) direction to oppose the temperature rise.

Give the Bronsted-Lowry definitions of an acid and a base.

An acid is a proton ($\ce{H+}$) donor; a base is a proton acceptor.

Define pH in terms of hydrogen ion concentration.

$\text{pH} = -\log_{10}[\ce{H+}]$.

Write the expression for the acid dissociation constant $K_a$ of a weak acid HA.

$K_a = \dfrac{[\ce{H+}][\ce{A-}]}{[\ce{HA}]}$, and $\text{p}K_a = -\log_{10}K_a$.

State the ionic product of water $K_w$ at $298\ \text{K}$.

$K_w = [\ce{H+}][\ce{OH-}] = 1.0\times10^{-14}\ \text{mol}^2\,\text{dm}^{-6}$.

What is a buffer solution and what is it typically made from?

A solution that resists changes in pH when small amounts of acid or alkali are added; typically a weak acid and its conjugate base (salt), e.g. $\ce{CH3COOH}$ / $\ce{CH3COONa}$.

Define standard electrode potential, $E^{\ominus}$.

The EMF of a half-cell connected to a standard hydrogen electrode under standard conditions ($298\ \text{K}$, $100\ \text{kPa}$, $1\ \text{mol dm}^{-3}$ solutions).

How do you calculate the EMF of an electrochemical cell from standard electrode potentials?

$E^{\ominus}_{\text{cell}} = E^{\ominus}_{\text{reduction (cathode)}} - E^{\ominus}_{\text{oxidation (anode)}}$, i.e. (more positive) $-$ (more negative).

Explain the trend in atomic radius across Period 3.

Atomic radius decreases because nuclear charge increases while shielding stays roughly constant (electrons added to the same shell), pulling electrons closer.

Why does melting point peak at silicon in Period 3?

Silicon has a giant covalent (macromolecular) structure with strong covalent bonds throughout, requiring large amounts of energy to break.

Describe the trend in reactivity down Group 2 and explain it.

Reactivity increases down the group: ionisation energies decrease as atomic radius and shielding increase, so atoms more readily lose their two outer electrons.

Describe the trend in solubility of Group 2 hydroxides and sulfates down the group.

Hydroxides become more soluble down the group; sulfates become less soluble down the group.

State the trend in boiling point of the Group 7 halogens and explain it.

Boiling point increases down the group because molecules gain more electrons, giving stronger London (van der Waals) forces.

Why does oxidising power decrease down Group 7?

Larger atoms with more shielding gain an electron less readily, so the halogens become weaker oxidising agents down the group.

What is observed when chlorine water is added to potassium bromide solution, and why?

The solution turns orange as bromine is displaced: $\ce{Cl2 + 2Br- -> 2Cl- + Br2}$, because chlorine is a stronger oxidising agent.

Define a transition metal.

A d-block metal that forms at least one stable ion with a partially filled d-subshell.

List four characteristic properties of transition metals.

Variable oxidation states, coloured compounds/ions, catalytic activity, and the formation of complex ions.

What is a ligand and what is the coordination number of a complex?

A ligand is a species that donates a lone pair of electrons to a central metal ion (dative bond); the coordination number is the number of coordinate bonds to the central ion.

Why are many transition metal complexes coloured?

The d-orbitals split into two energy levels by ligands; an electron absorbs a frequency of visible light to be promoted, and the complementary colour of the absorbed light is transmitted/seen.

Define homologous series.

A family of organic compounds with the same general formula and functional group, differing by $\ce{CH2}$, showing a gradual change in physical properties and similar chemical reactions.

Distinguish between empirical and molecular formula.

The empirical formula is the simplest whole-number ratio of atoms of each element; the molecular formula is the actual number of each type of atom in a molecule.

Define structural isomers and stereoisomers.

Structural isomers have the same molecular formula but different structural arrangements of atoms; stereoisomers have the same structure but a different spatial arrangement (e.g. E/Z or optical isomers).

Why are E/Z (cis-trans) isomers possible in alkenes but not alkanes?

The $\ce{C=C}$ double bond cannot rotate; if each carbon carries two different groups, the groups are locked in different spatial positions, giving E/Z isomers.

State the mechanism and reagent for the reaction of bromine with ethene.

Electrophilic addition: $\ce{C2H4 + Br2 -> C2H4Br2}$ (1,2-dibromoethane), the basis of the bromine water test for unsaturation.

What is the mechanism of the reaction of methane with chlorine in UV light, and why is it limited?

Free-radical substitution (initiation, propagation, termination); it gives a mixture of products and is hard to control as further substitution occurs.

Name the type of reaction and product when a primary alcohol is oxidised with acidified potassium dichromate(VI) and distilled off immediately.

Oxidation to an aldehyde; e.g. $\ce{CH3CH2OH ->[\text{[O]}] CH3CHO + H2O}$; the orange dichromate turns green ($\ce{Cr^{3+}}$).

How do you distinguish an aldehyde from a ketone using Tollens' reagent?

An aldehyde reduces Tollens' reagent (ammoniacal silver nitrate) producing a silver mirror; a ketone gives no reaction.

Give the structure of the carboxyl functional group and the products of its reaction with a carbonate.

$\ce{-COOH}$; reaction with a carbonate gives a carboxylate salt, water and carbon dioxide (effervescence), e.g. $\ce{2CH3COOH + Na2CO3 -> 2CH3COONa + H2O + CO2}$.

What makes benzene resistant to addition reactions, favouring substitution?

Its delocalised ring of six $\pi$-electrons is energetically stable; substitution preserves this delocalisation whereas addition would disrupt it.

Name the mechanism and product when benzene reacts with a mixture of concentrated $\ce{HNO3}$ and $\ce{H2SO4}$.

Electrophilic substitution (nitration) producing nitrobenzene $\ce{C6H5NO2}$; the electrophile is the nitronium ion $\ce{NO2+}$.

How are amines classified as primary, secondary and tertiary, and how can they act as bases?

By the number of carbon groups attached to nitrogen (one, two, three); the nitrogen lone pair accepts a proton, so amines act as Bronsted-Lowry bases.

Compare addition and condensation polymerisation.

Addition polymerisation joins unsaturated monomers ($\ce{C=C}$) with no loss of atoms; condensation polymerisation joins monomers with two functional groups, eliminating a small molecule (e.g. $\ce{H2O}$ or $\ce{HCl}$) such as in polyesters and polyamides.

What links does an ester and an amide formation each involve in condensation polymers?

Polyesters contain the ester linkage $\ce{-COO-}$ (from diol + dicarboxylic acid); polyamides contain the amide linkage $\ce{-CONH-}$ (from diamine + dicarboxylic acid).

What structural information does infrared (IR) spectroscopy provide?

It identifies functional groups by the wavenumbers of bonds that absorb IR radiation, e.g. a broad $\ce{O-H}$ in carboxylic acids ($2500$-$3300\ \text{cm}^{-1}$) and $\ce{C=O}$ around $1700\ \text{cm}^{-1}$.

In a mass spectrum, what does the molecular ion peak (M$^+$) tell you, and what causes the M+1 peak?

The M$^+$ peak gives the relative molecular mass; the small M+1 peak is due to the presence of the $\ce{^{13}C}$ isotope.

What does the number of peaks in a $^1$H NMR spectrum indicate, and what does splitting (the n+1 rule) reveal?

The number of peaks shows the number of chemically different hydrogen environments; splitting into $n+1$ lines reveals $n$ hydrogens on adjacent carbon atoms.

In NMR spectroscopy, what is the reference standard and why is TMS used?

Tetramethylsilane (TMS, $\ce{Si(CH3)4}$) is the standard set at $\delta = 0$; it is inert, volatile, non-toxic and gives a single sharp peak from 12 equivalent protons away from most other signals.

How does paper/thin-layer chromatography separate components, and what is the $R_f$ value?

Separation depends on the differing affinities of components for the mobile and stationary phases; $R_f = \dfrac{\text{distance moved by spot}}{\text{distance moved by solvent front}}$.

What is the difference between the stationary and mobile phases in chromatography?

The stationary phase is fixed (e.g. paper, silica); the mobile phase (a liquid or gas) moves through it carrying the components, which separate according to their relative attraction to each phase.

What test and result identifies a halide ion using silver nitrate solution?

Add dilute $\ce{HNO3}$ then $\ce{AgNO3(aq)}$: $\ce{Cl-}$ gives a white precipitate, $\ce{Br-}$ cream, $\ce{I-}$ yellow; solubility in ammonia then confirms (chloride dissolves in dilute, bromide in concentrated, iodide insoluble).

How do you test for a carbonate ion and confirm the gas evolved?

Add dilute acid; effervescence of $\ce{CO2}$ occurs ($\ce{CO3^2- + 2H+ -> H2O + CO2}$); bubbling the gas through limewater turns it cloudy.

State the test and positive result for ammonium ions ($\ce{NH4+}$).

Warm with sodium hydroxide solution; ammonia gas is released which turns damp red litmus paper blue: $\ce{NH4+ + OH- -> NH3 + H2O}$.

How is sulfate ($\ce{SO4^2-}$) identified in solution?

Add dilute $\ce{HCl}$ then barium chloride solution; a white precipitate of barium sulfate forms: $\ce{Ba^2+ + SO4^2- -> BaSO4}$.