Chemistry (9701) Past Papers & Revision Resources

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List chain and ring skeletons first.

Check each C=C, and rings with substituents on two different carbons, for cis/trans, and each carbon for four different groups (a chiral centre).

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Only temperature changes Kc or Kp.

Water belongs in Kc unless it is the solvent.

For mole fractions, divide by the total moles of every gas present.

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Acidified dichromate(VI) oxidises only primary and secondary alcohols and aldehydes.

NaBH₄ or LiAlH₄ reduce aldehydes and ketones, and LiAlH₄ also carboxylic acids, to alcohols with the same carbon count.

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Look for CH₃CO- or CH₃CH(OH)-.

Ethanol, ethanal, propanone and propan-2-ol react; propan-1-ol, propanal and pentan-3-one do not.

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Multiply each value by its coefficient in the equation.

Divide a neutralisation heat change by the moles of water formed.

Elements in their standard states have zero ΔHf.

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Begin every arrow at a bond or lone pair and point it to where those electrons end up.

Mark δ+ and δ− on polar bonds, and lone pairs on nucleophiles.

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Compare the possible carbocations.

Alkyl groups' inductive effect stabilises the positive carbon, so stability increases from primary to secondary to tertiary.

The most stable cation gives the major product.

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Single bond: one σ.

Double bond: one σ plus one π.

Triple bond: one σ plus two π.

A π bond comes from sideways overlap of p orbitals.

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Write X(g) → X⁺(g) + e⁻.

Then compare nuclear charge, distance of the electron from the nucleus, shielding by inner shells, and spin-pair repulsion when it leaves a paired orbital.

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Melting or boiling simple molecules overcomes forces between molecules: name them (id-id, pd-pd or hydrogen bonds; polar molecules have both id-id and pd-pd).

Giant structures need strong bonds broken.

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Record every burette reading, rough titration included, to two decimal places with the last digit 0 or 5.

Write both the initial and final reading each time.

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Repeat until two accurate titres agree within 0.10 cm³.

Average only those concordant titres, and show which ones you used.

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Use 'colourless' for a solution with no colour, 'effervescence' or 'bubbles' for gas, and 'white precipitate' for limewater.

Copy terms from the qualitative analysis notes printed in the paper.

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Warm the mixture with NaOH(aq) and hold damp red litmus paper in the mouth of the tube, away from the liquid.

Record that the gas turned it blue.

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m is the mass of the liquid: take 1.00 g per cm³, adding the volumes of all solutions mixed.

Read thermometers marked in 1 °C steps to 0.5 °C.

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First arrow: from the ring's delocalised electrons to the electrophile.

The horseshoe leaves out the sp³ carbon and holds the +.

Last arrow: from the C-H bond into the ring.

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Define it by its ions: a d-block element forming one or more stable ions with incomplete d orbitals.

Ions lose 4s electrons first, so Fe²⁺ is [Ar]3d⁶.

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Kstab = [complex] / ([metal ion][ligand]ⁿ), with no [H₂O] and each charge inside its bracket.

Coordination number counts dative bonds: three bidentate en ligands make six.

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Smaller ions with higher charges give a more exothermic lattice energy.

Count every ion: for MgCl₂, a Born-Haber cycle needs twice the chlorine atomisation and electron affinity; a dissolving cycle needs 2ΔHhyd(Cl⁻).

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Divide ΔS by 1000 so all terms are in kJ, and use T in kelvin.

Plotting ΔG against T gives a gradient of −ΔS and an intercept of ΔH.

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Independent: the variable you deliberately change.

Dependent: the quantity you directly measure, such as a gas volume or a time.

Values like rate are worked out from it afterwards.

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Dissolve in a little distilled water first.

Transfer to a volumetric flask, rinse the beaker and rod into it, make up to the mark, then invert to mix.

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Double the single-reading uncertainty: two burette readings of ±0.05 cm³ give a titre uncertainty of ±0.10 cm³.

Then percentage uncertainty = uncertainty ÷ measured value × 100.

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Choose two points on your best-fit line, at least half its length apart, and quote their coordinates.

Include any factor such as ×10⁻³ shown in the axis label.

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Identify the anomaly and give a cause that fits its direction: gas lost before the bung went on gives too low a volume.

Leave it out of your best-fit line.