Glossary
Brief definitions of terms that appear throughout the experiments and chemical pages. Each entry has a stable anchor, so pages can link straight to it — for example glossary.html#redox.
Amphoteric
Able to react as either an acid or a base. Aluminium and its oxide are amphoteric: they dissolve in both strong acids and strong bases.
Anode / Cathode
The two electrodes in an electrochemical cell. Oxidation happens at the anode; reduction happens at the cathode. In anodizing the workpiece is the anode.
Buffer
A solution that resists changes in pH when small amounts of acid or base are added, because it contains both a weak acid and its conjugate base.
Catalyst
A substance that speeds up a reaction without being consumed by it. Yeast’s enzymes and the iodide ion in the iodine clock act as catalysts.
Chelation
The binding of a metal ion by a molecule that grips it at several points at once, like a claw. EDTA chelates calcium in hard-water titration.
Colloid
A mixture in which very small particles are dispersed through another substance without dissolving. Colloids scatter light (see Tyndall effect); true solutions do not.
Complex ion
A central metal ion surrounded by bound molecules or ions called ligands. Many vivid colours — the deep blue of copper–ammonia — come from complex ions.
Desiccant
A hygroscopic material used to keep its surroundings dry by absorbing water vapour, such as the calcium chloride in the gravimetric humidity experiment.
Electrolyte
A substance that conducts electricity when dissolved or molten because it splits into mobile ions. Salt water is an electrolyte; sugar water is not.
Electrolysis
Driving a non-spontaneous chemical reaction by passing an electric current through an electrolyte, as in splitting water into hydrogen and oxygen.
Endothermic
Describing a process that absorbs heat from its surroundings, making them feel cold — for example ammonium chloride dissolving in a cold pack.
Exothermic
Describing a process that releases heat to its surroundings, making them feel warm — for example calcium chloride dissolving in water.
Hydrate
A compound that incorporates water molecules into its crystal structure. Heating a hydrate often drives off the water and changes its colour, as with cobalt chloride.
Hygroscopic
Readily absorbing moisture from the air. Hygroscopic salts clump and eventually dissolve in their own absorbed water (deliquescence).
Indicator
A substance that changes colour to signal a chemical condition, most often pH. Red cabbage juice and phenolphthalein are indicators.
Ligand
A molecule or ion that bonds to a central metal atom to form a complex ion. Water and ammonia are common ligands.
Molarity
A measure of concentration: the number of moles of a dissolved substance per litre of solution (mol/L, written M).
Monoprotic / Triprotic
Describing how many hydrogen ions an acid can donate. Acetic acid is monoprotic (one H⁺); citric acid is triprotic (three), which changes the ratios in a neutralization.
Neutralization
The reaction of an acid with a base to produce a salt and water, moving the pH toward neutral (7).
Nucleation
The first formation of a tiny stable seed from which a crystal (or bubble) grows. A single seed can trigger a whole supersaturated solution to crystallize.
Oxidation
The loss of electrons by an atom, ion, or molecule (its oxidation state rises). Always paired with reduction. See redox.
pH
A scale from 0 to 14 measuring how acidic (low) or basic (high) a solution is; 7 is neutral. Each unit is a tenfold change in acidity.
Phase-change material
A substance used to store and release heat as it melts and freezes at a fixed temperature, such as Glauber’s salt.
Piezoelectric
Generating an electric voltage in response to mechanical stress. Rochelle salt crystals are piezoelectric and can work as a microphone.
Polymorphism
The ability of a solid to exist in more than one crystal structure — for example the rhombic and monoclinic forms of sulfur.
Precipitate
An insoluble solid that forms and separates out when two solutions are mixed. The reaction that produces it is a precipitation reaction.
Redox
A reaction in which electrons transfer from one species to another, coupling an oxidation (electron loss) with a reduction (electron gain). Short for reduction–oxidation.
Reduction
The gain of electrons by an atom, ion, or molecule (its oxidation state falls). Always paired with oxidation. See redox.
Saponification
The reaction of a fat or oil with a strong base to produce soap and glycerol.
Solubility
The maximum amount of a substance that will dissolve in a given amount of solvent at a given temperature. It usually rises with temperature — but not always (see supersaturation).
Sublimation
A substance passing directly from solid to vapour without melting, as menthol and iodine do.
Supersaturation
A solution holding more dissolved substance than it normally could at that temperature — an unstable state that crystallizes suddenly when disturbed, as in hot ice.
Titration
Measuring an unknown concentration by adding a reagent of known concentration until a reaction just completes, signalled by an indicator colour change.
Tyndall effect
The scattering of a light beam by the suspended particles of a colloid, making the beam’s path visible.