Glossary STU

                                    S

salt

a compound, often involving a metal, that is the reaction product of an acid and a base, or of two elements. (Note 'salt' is also the common word for sodium chloride, common salt or table salt.)
Example: sodium chloride (NaCl) and potassium sulphate (K₂SO₄)

salt bridge

a permeable material soaked in a salt solution that allows ions to be transferred from one container to another. The salt solution remains unchanged during this transfer. Example: sodium sulphate used as a salt bridge in a galvanic cell.

saponification

a reaction between a fat and a base that produces a soap.

saturated

a state in which a liquid can hold no more of a substance. If any more of the substance is added, it will not dissolve.

saturated hydrocarbon

a hydrocarbon in which the carbon atoms are held with single bonds. Example: ethane (C₂H₆).

saturated solution

a solution that holds the maximum possible amount of dissolved material. When saturated, the rate of dissolving solid and that of recrystallisation solid are the same, and a condition of equilibrium is reached. The amount of material in solution varies with the temperature; cold solutions can hold less dissolved solid material than hot solutions. Gases are more soluble in cold liquids than in hot liquids.

sediment

material that settles out at the bottom of a liquid when it is still. A precipitate is one form of sediment.

semiconductor

a material of intermediate conductivity. Semiconductor devices often use silicon when they are made as part of diodes, transistors or integrated circuits. Elements intermediate between metals and non-metals are also sometimes called semiconductors.
Example: germanium oxide, germanium.

semipermeable membrane

a thin material that acts as a fine sieve or filter, allowing small molecules to pass, but holding large molecules back.

separating column

used in chromatography. A tall glass tube containing a porous disc near the base and filled with a substance (for example, aluminium oxide, which is known as a stationary phase) that can adsorb materials on its surface. When a mixture is passed through the column, fractions are retarded by differing amounts, so that each fraction is washed through the column in sequence.

separating funnel

a pear-shaped, glassware funnel designed to permit the separation of immiscible liquids by simply pouring off the more dense liquid while leaving the less dense liquid in the funnel.

series circuit

an electrical circuit in which all of the components are joined end to end in a line.

shell

the term used to describe the imaginary ball-shaped surface outside the nucleus of an atom that would be formed by a set of electrons of similar energy. The outermost shell is known as the valence shell. Example: neon has shells containing 2 and 8 electrons.

side-arm boiling tube

a boiling tube with an integral glass pipe near its open end. The side arm is normally used for the entry or exit of a gas.

simple distillation

the distillation of a substance when only one volatile fraction is to be collected. Simple distillation uses a Liebig condenser arranged almost horizontally. When the liquid mixture is heated and vapours are produced, they enter the condenser and then flow away from the flask and can be collected. Example: simple distillation of ethanoic acid.

slag

a mixture of substances that are waste products of a furnace. Most slags are composed mainly of silicates.

smelting

roasting a substance in order to extract the metal contained in it.

smog

a mixture of smoke and fog. The term is used to describe city fogs in which there is a large proportion of particulate matter (tiny pieces of carbon from exhausts) and also a high concentration of sulphur and nitrogen gases and probably ozone.

smokeless fuel

a fuel which has been subjected to partial pyrolysis, such that there is no more loose particulate matter remaining. Example: Coke is a smokeless fuel.

solid/solid phase

a rigid form of matter which maintains its shape, whatever its container.

solubility

a measure of the maximum amount of a substance that can be contained in a solvent.

soluble

readily dissolvable in a solvent.

solute

a substance that has dissolved. Example: sodium chloride in water.

solution

a mixture of a liquid (the solvent) and at least one other substance of lesser abundance (the solute). Mixtures can be separated by physical means, for example, by evaporation and cooling.

solvent

the main substance in a solution.

Temperature measure of the random motions (average kinetic energy) of the components of a substance.

Tertiary structure (of a protein) the overall shape of a protein, long and narrow or globular, maintained by different types of intramolecular interactions.

Theoretical yield the maximum amount of a given product that can be formed when the limiting reactant is completely consumed.

Theory (model) a set of assumptions put forth to explain some aspect of the observed behavior of matter.

Thermodynamics a study of energy and its interactions.

Titration a technique in which one solution is used to analyze another.

Torr another name for millimeters of mercury (mm Hg).

Trace elements metals present only in trace amounts in the human body.

Transition metals several series of elements in which inner orbitals (d or f orbitals) are being filled.

Transuranium elements the elements beyond uranium that are made artificially by particle bombardment.

Triple bond a bond in which two atoms share three pairs of electrons.



U [return to top]

Uncertainty (in measurement) the characteristic reflecting the fact that any measurement involves estimates and cannot be exactly reproduced.

Unit factor an equivalence statement between units that is used for converting from one set of units to another.

Universal gas constant the combined proportionality constant in the ideal gas law; 0.08206 L atm/K mol, or 8.314 J/K mol.

Unsaturated solution a solution in which more solute can be dissolved than is dissolved