Glossary of Common Chemical Terms

An acid is a substance with a pH of less than 7. Acids are denoted on a litmus test by turning it red and are typically sour or tart tasting (food grades) or corrosive.

An alkali is a substance with a pH greater than 7. Alkalis can neutralise an acid and  are denoted on a litmus test by turning it blue. Although they can 'cancel out' an acid, certain alkalis are strong bases which can also be highly corrosive.

Anhydrous, taken from the Greek ‘an’ which means without and ‘hydor’ which means water. Anhydrous means a substance which contains little or no water.

Aqueous describes a solution or mixture which involves water. When a chemical has been dissolved in water it is referred to as ‘aqueous solution’ or ‘aq’ for short. Examples include Hydrochloric Acid which is the aqueous solution of hydrogen chloride.

A base is a substance with a pH greater than 7 and the ability to neutralise an acid. Although similar, not all bases are alkali (but all alkalis are bases). The difference – many bases do not dissolve in water, but if a base does dissolve in water, we call it an alkali.

A buffering agent is a substance that can resist changes in pH when small amounts of an acid or base are added to a solution. For example, buffers are heavily used within the personal care and cosmetics industry where they help maintain the neutral pH of a product by preventing them from becoming too acid or alkaline.

A catalyst is a substance that alters the rate of a chemical reaction without being consumed or altering the compounds in the reaction. It creates an alternative path the reactants to follow which either slow down or speed up the process.

A chelating agent is a compound that forms a ring-like structure around a metal ion. We call this a chelate. The role of a chelate is to inactivate the metal ion to prevent unwanted chemical reactions.

A coagulant causes small suspended particles (colloidal) in a liquid mixture to clump together (coagulate) and form a semi-solid mass.

A colloid is a mixture in which small particles of a substance are evenly dispersed throughout another substance.

A dispersing agent, also known as a dispersant or surfactant is added to a liquid to keep the solid particles suspended within it. The function of the dispersant is to reduce the attraction between solid particles, preventing them from clumping together.

Effervescence is the process of releasing bubbles of gas from a liquid by a chemical reaction.

An emulsion is a mixture of two or more liquids which usually do not mix (for example oil and water)

An ether is a compound made up of an oxygen atom connected to two carbon-based groups, often called alkyl or aryl. 

A flocculant, or flocculation, is a process where a coagulant is added to a water mixture to help particles bond together and create larger solid masses which are easier to separate. This clumped together matter is called floc. Flocculants are often used in water treatment to separate solid particles from liquids and to purify the liquid.

Hydrate is a compound which includes water as part of its crystalline structure.

Same as hydrate, hydrous compounds contain water molecules.

Monohydate means a chemical compound with water, but as the name ‘mono’ suggests which is of Greek origin meaning ‘one’, ‘single’ or ‘alone’ it possesses one water molecule per one molecule of compound.

An oxidising agent oxidises is a molecule or ion that can accept electrons from another substance thereby oxidising it. They are used to initiate or drive chemical reactions and as reagents.

Ancient Greek for the word five this means a chemical compound with five water molecules per molecule of compound.

Polymers are characterised by being flexible, water-proof and resistant to chemicals. They are long chains made up of repeating compounds called monomers. The properties of a polymer depend on the type of monomers and how they are linked together – stiff or flexible, transparent or opaque, strong or weak and so on.

Reactivity is the rate in which a substance goes through a chemical change when mixed with another substance.

A reagent is a substance used to carry out laboratory tests. When added to a solution reagents trigger a chemical reaction to help detect either the presence or absence of certain substances.

A reducing agent reduces another atom or ion by causing it to gain electrons.

A sequestrant is a compound used to bind and remove metal ions from a solution to keep them from reacting or forming solid particles. This allows the metal ions to be easily recovered and prevents the formation of unwanted impurities in a solution.

A solvent is used to dissolve, dilute or disperse other compounds such as solids, gases or other liquids. Common examples of solvents are water, alcohol and acetone.

Titration is a laboratory method of quantitative chemical analysis. It involves slowly adding a known concentration of a second substance (this is called a titrant) to the first substance until a specific reaction occurs, such as change in colour. Through this measurement, the concentration of the first substance can be calculated.