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Cambridge Pre-U Chemistry (Principal Subject) Flashcards
61 question-and-answer cards covering Chemistry (Principal Subject) as it is examined in Cambridge Pre-U. 24 of them are printed below, taken from across the deck — no signup, no paywall on the preview.
24 sample cards from the Chemistry (Principal Subject) deck
Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.
What is a ligand, and what is the coordination number of $\ce{[Cu(H2O)6]^{2+}}$?
A ligand is a species with a lone pair that forms a dative bond to a central metal ion. The coordination number of $\ce{[Cu(H2O)6]^{2+}}$ is $6$ (octahedral).
Explain why transition metal complexes are coloured.
Ligands split the $d$ orbitals into two energy levels of gap $\Delta E$; $d$–$d$ electron transitions absorb visible light of frequency $\Delta E = hf$, and the complementary colour is transmitted/observed.
Write the half-equation and colour change when acidified $\ce{MnO4-}$ acts as an oxidant.
$$\ce{MnO4- + 8H+ + 5e- -> Mn^{2+} + 4H2O}$$ Colour changes from purple ($\ce{MnO4-}$) to very pale pink/colourless ($\ce{Mn^{2+}}$).
Define oxidation and reduction in terms of electron transfer and oxidation number.
Oxidation is loss of electrons / an increase in oxidation number; reduction is gain of electrons / a decrease in oxidation number (OIL RIG).
Define standard electrode potential, $E^{\ominus}$.
The EMF of a half-cell relative to the standard hydrogen electrode under standard conditions ($298\,\text{K}$, $1\,\text{mol dm}^{-3}$ solutions, $100\,\text{kPa}$ gases), with the SHE defined as $0\,\text{V}$.
How is the standard cell EMF calculated from two electrode potentials?
$$E^{\ominus}_{\text{cell}} = E^{\ominus}_{\text{cathode (reduction)}} - E^{\ominus}_{\text{anode (oxidation)}}$$ A positive $E^{\ominus}_{\text{cell}}$ indicates a feasible reaction.
Define the term 'homologous series' and give the general formula of the alkanes.
A family of organic compounds with the same functional group and general formula, differing by $\ce{CH2}$, with similar chemical properties and a gradual trend in physical properties. Alkanes: $C_{n}H_{2n+2}$.
Describe the mechanism type and propagation steps for the free-radical chlorination of methane.
Free-radical substitution (initiated by UV). Propagation: $\ce{Cl. + CH4 -> .CH3 + HCl}$ then $\ce{.CH3 + Cl2 -> CH3Cl + Cl.}$.
Define electrophile and state the mechanism for $\ce{Br2}$ adding to ethene.
An electrophile is an electron-pair acceptor (electron-deficient species). Ethene + $\ce{Br2}$ undergoes electrophilic addition to give 1,2-dibromoethane: $\ce{CH2=CH2 + Br2 -> CH2BrCH2Br}$.
State Markovnikov's rule for addition of $\ce{HBr}$ to an unsymmetrical alkene.
The hydrogen adds to the carbon already bearing the most hydrogens, so the more stable (more substituted) carbocation forms, giving the major product (e.g. 2-bromopropane from propene).
Give reagents/conditions for oxidising a primary alcohol to an aldehyde and then to a carboxylic acid.
Acidified $\ce{K2Cr2O7}$ (or $\ce{KMnO4}$). Aldehyde: distil off as formed (limited oxidant). Carboxylic acid: heat under reflux with excess oxidant. Orange dichromate turns green ($\ce{Cr^{3+}}$).
How do Tollens' and Fehling's reagents distinguish aldehydes from ketones?
Aldehydes are oxidised and give positive tests (Tollens': silver mirror; Fehling's: brick-red $\ce{Cu2O}$ precipitate); ketones give no reaction with either.
Describe the electrophilic substitution mechanism for nitration of benzene, including the electrophile.
Benzene reacts with the nitronium ion $\ce{NO2+}$ (from $\ce{HNO3 + H2SO4}$) by electrophilic substitution: $\ce{NO2+}$ adds to form an unstable intermediate, then $\ce{H+}$ is lost to restore aromaticity, giving nitrobenzene.
Distinguish between structural isomerism and stereoisomerism, naming the two types of stereoisomerism.
Structural isomers have the same molecular formula but different atom connectivity. Stereoisomers have the same connectivity but different spatial arrangement: (i) geometric (cis–trans / $E$–$Z$) and (ii) optical (enantiomers).
What structural feature gives rise to optical isomerism, and what is a key physical property of enantiomers?
A chiral centre — a carbon bonded to four different groups. Enantiomers are non-superimposable mirror images that rotate the plane of plane-polarised light in equal but opposite directions.
Distinguish addition and condensation polymerisation, giving the repeat-unit feature of each.
Addition: monomers with C=C join with no loss of atoms (e.g. poly(ethene)). Condensation: monomers with two functional groups join with loss of a small molecule (e.g. $\ce{H2O}$ or $\ce{HCl}$), forming polyesters/polyamides.
Identify the bond responsible for an absorption near $1700\,\text{cm}^{-1}$ in an infrared spectrum.
The carbonyl $\ce{C=O}$ stretch (found in aldehydes, ketones, carboxylic acids and esters), typically $1680$–$1750\,\text{cm}^{-1}$.
In $^{1}\text{H}$ NMR, what do (a) the number of peaks, (b) the integration, and (c) the splitting tell you?
(a) Number of peaks = number of chemically distinct hydrogen environments; (b) integration (area) = relative number of H in each environment; (c) splitting follows the $n+1$ rule, indicating the number of H on adjacent carbons.
What information does the molecular ion peak (M$^{+}$) provide in mass spectrometry?
The mass/charge ratio of the molecular ion gives the relative molecular mass ($M_{r}$) of the compound; the highest $m/z$ peak (ignoring isotope peaks) corresponds to $M^{+}$.
Give the reagents and positive observations for testing a halide ion in solution.
Add dilute $\ce{HNO3}$ then $\ce{AgNO3(aq)}$: $\ce{Cl-}$ white ppt (soluble in dilute $\ce{NH3}$), $\ce{Br-}$ cream ppt (soluble in conc. $\ce{NH3}$), $\ce{I-}$ yellow ppt (insoluble in $\ce{NH3}$).
Describe the test for an ammonium ion ($\ce{NH4+}$).
Warm with $\ce{NaOH(aq)}$: ammonia gas is released which turns damp red litmus paper blue: $\ce{NH4+ + OH- -> NH3 + H2O}$.
State the formula for percentage yield and percentage atom economy.
$$\%\,\text{yield} = \frac{\text{actual moles of product}}{\text{theoretical moles of product}}\times100$$ $$\%\,\text{atom economy} = \frac{M_{r}\,\text{of desired product}}{\text{total }M_{r}\,\text{of all products}}\times100$$
How is the end point in an acid–base titration found, and how is the concentration of an unknown calculated?
An indicator (or pH meter) marks the end point at the equivalence volume. Using $n = c\times V$ and the balanced mole ratio: $$c_{1} = \frac{c_{2}V_{2}}{V_{1}}\times\frac{\text{ratio}_{1}}{\text{ratio}_{2}}$$
Distinguish between random and systematic errors in an experiment, with an example of each.
Random errors scatter readings unpredictably and are reduced by repeats/averaging (e.g. judging a colour change). Systematic errors shift all readings the same way and are not reduced by repeats (e.g. an uncalibrated balance giving a fixed offset).
What this deck covers
The Chemistry (Principal Subject) deck follows the Cambridge Pre-U Chemistry (Principal Subject) syllabus — 4 chapters and 18 topics — so questions land on material that is genuinely examinable rather than trivia around it. That works out to roughly 15.3 cards per chapter.
Answers are written to be recallable, not just readable — averaging about 188 characters, which is long enough to carry the reasoning and short enough to say out loud.
A deck like this earns its keep on the second and third pass. Read the syllabus first so you know the shape of the subject, then use the cards to find the specific facts that have not stuck.
Chemistry (Principal Subject) flashcards FAQ
How many Chemistry (Principal Subject) flashcards are in this Cambridge Pre-U deck?
61 cards. This page previews 24 of them, sampled evenly across the deck so you can judge the difficulty before installing anything.
Are these Cambridge Pre-U flashcards free?
Yes. The preview here is free to read with no signup, and the full 61-card deck is free inside the Examius app.
What do the Chemistry (Principal Subject) cards cover?
They follow the Cambridge Pre-U Chemistry (Principal Subject) syllabus — 4 chapters and 18 topics — so the questions track what is actually examinable.
How should I use these flashcards?
Read the syllabus first so you know the shape of the subject, then drill the deck. Examius schedules each card with spaced repetition, so cards you keep missing come back sooner and ones you know drift further apart.