The pH scale: Chemical Changes: Chemistry: GCSE (9:1)

Acid

A substance that increases the hydrogen ion concentration of a solution.

Base

A substance that reacts with an acid and neutralises it

Alkali

A soluble base, that produces OH- ions in solution

Types of chemicals that are bases

Metal oxides, metal hydroxides, metal carbonates, ammonia

Types of chemicals that are alkalis

Metal hydroxides, ammonia

Strong acids

Acids that fully ionise in water

Weak acids

Acids that only slightly ionise in aqueous solution

Ionise

Split into ions

pH

A measure of H+ concentration

Ions produced by acids

H+

Ions produced by alkalis

OH-

Neutral pH

7

pH of acids

less than 7

pH of alkalis

more than 7

Neutralisation reaction

The reaction of an acid and a base forming a salt and water

Ionic equation for an acid and an alkali

H+(aq) + OH-(aq) --> H2O(l)

Universal indicator

An indicator with a different colour for each pH value.

If pH decreases by 1

hydrogen ion concentration increases x10

At pH 7

concentration of H+ = concentration of OH-

Strong acid

An acid that ionises completely in water

Weak acid

An acid that only partially ionises in water