Everything from the 6 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
Choose apparatus to match the quantity and the precision needed. Time is measured with a stopwatch or stop-clock, temperature with a thermometer, mass with a balance, and volume with a burette (variable volumes, to 0.05 cm3), a volumetric pipette (one fixed volume, very accurately), a measuring cylinder (quick but less precise) or a gas syringe (volumes of gas). A solvent dissolves a solute to make a solution; a saturated solution holds the maximum amount of solute at that temperature. After filtration, the solid left in the filter paper is the residue and the liquid that passes through is the filtrate.
The filtrate is what passes through the paper, the residue is what stays behind: do not swap them. A measuring cylinder is not suitable for a titration, and a gas collected over water must be only slightly soluble (carbon dioxide and ammonia are better measured with a gas syringe). Always give a volume read from a burette to 2 decimal places, ending in 0 or 5.
In an acid-base titration a volumetric pipette transfers a fixed volume of alkali (for example 25.0 cm3) into a conical flask, a few drops of indicator are added, and acid is run in from a burette until the indicator just changes colour: the end-point. The volume of acid added is the titre (final reading minus initial reading). A rough titre is followed by accurate titrations, adding acid drop by drop near the end-point, until concordant results (titres within 0.10 cm3 of each other) are obtained; their mean is used. Methyl orange is red in acid and yellow in alkali; thymolphthalein is colourless in acid and blue in alkali. Litmus is not used for titrations because its colour change is not sharp.
The rough titre overshoots the end-point, so leave it out of the mean. Titre = final reading minus initial reading, not the final reading alone. Use the mole ratio from the equation: with H2SO4, moles of NaOH are twice the moles of acid. And convert cm3 to dm3 by dividing by 1000.
In paper chromatography spots of the samples are placed on a pencil baseline, and the paper stands in a solvent whose level is below the baseline. The solvent moves up the paper and carries each substance a different distance, depending on its solubility in the solvent and its attraction to the paper. A pure substance gives one spot; a mixture gives several. An unknown is identified when its spots match those of known substances at the same heights. Extended: colourless substances are made visible with a locating agent, and each substance has an Rf value = distance moved by the substance ÷ distance moved by the solvent front.
Measure both distances from the baseline, not from the bottom of the paper, and measure to the centre of the spot. Rf is spot ÷ solvent front, so it can never be bigger than 1: if you get 2.5, you divided the wrong way round. A substance that gives one spot in one solvent may still be a mixture; a second solvent can split it.
Choose a separation method from the difference between the substances. Filtration separates an insoluble solid from a liquid. Crystallisation obtains a soluble solid from its solution: heat to evaporate some solvent until the solution is saturated, then cool so crystals form. Simple distillation separates a solvent from a solution (for example water from salt water). Fractional distillation separates miscible liquids with different boiling points (for example ethanol and water). Dissolving in a suitable solvent separates a soluble solid from an insoluble one. A pure substance melts and boils at fixed, sharp temperatures; impurities lower the melting point and make it melt over a range, and raise the boiling point. Purity matters for food and drugs.
Do not heat a solution to dryness when crystallising a hydrated salt: you lose the water of crystallisation and may decompose it. Condenser water goes in at the bottom so the jacket stays full. Impurities lower the melting point (and widen the range) but raise the boiling point.
Anions: carbonate fizzes with dilute acid, giving CO2 that turns limewater milky; halides are acidified with dilute nitric acid and tested with aqueous silver nitrate (chloride white, bromide cream, iodide yellow precipitate); sulfate is acidified and gives a white precipitate with aqueous barium nitrate; sulfite turns acidified aqueous potassium manganate(VII) from purple to colourless; nitrate warmed with aqueous sodium hydroxide and aluminium foil gives ammonia. Cations are tested with aqueous sodium hydroxide and aqueous ammonia: the colour of the precipitate, and whether it dissolves in excess, identifies the ion. Flame tests identify Li+, Na+, K+, Ca2+, Ba2+ and Cu2+ by colour.
Halides are acidified with nitric acid, never hydrochloric (it adds chloride ions) or sulfuric acid. For sulfate, use barium nitrate after acidifying. Fe2+ gives a green precipitate and Fe3+ a red-brown one; do not swap them. Copper(II) hydroxide is light blue; the dark blue solution appears only with excess ammonia. Sodium's strong yellow flame can hide other colours, so the wire must be clean.
Ammonia turns damp red litmus paper blue. Carbon dioxide turns limewater milky. Chlorine bleaches damp litmus paper. Hydrogen gives a squeaky pop with a lighted splint. Oxygen relights a glowing splint. Sulfur dioxide turns acidified aqueous potassium manganate(VII) from purple to colourless. The litmus must be damp, because a gas has to dissolve in water before it can act as an alkali, acid or bleach.
A lighted splint is for hydrogen (squeaky pop); a glowing splint is for oxygen (relights). It is the limewater that turns milky, not the gas. Ammonia turns red litmus blue, so blue litmus would show no change. Chlorine bleaches litmus; "turns red" alone does not score.