aChem

Acid

A chemical substance that ionises in water to produce hydrogen ions ($H^+$).

Base

A metal oxide or metal hydroxide that reacts with an acid to produce salt and water only.

Alkali

A base that is soluble in water and ionises to produce hydroxide ions ($OH^-$).

Requirement for acidic properties

Presence of water, which allows the acid to ionise and release free-moving hydrogen ions ($H^+$).

Monoprotic acid

An acid that produces one mole of hydrogen ions ($H^+$) per mole of acid during ionisation.

Diprotic acid

An acid that produces two moles of hydrogen ions ($H^+$) per mole of acid during ionisation.

Strong acid

An acid that completely ionises in water to produce a high concentration of hydrogen ions ($H^+$).

Weak acid

An acid that partially ionises in water to produce a low concentration of hydrogen ions ($H^+$).

pH value

A logarithmic measure of the concentration of hydrogen ions ($H^+$) in an aqueous solution.

Effect of increasing hydrogen ion concentration on pH

The pH value decreases, indicating a more acidic solution.

Neutralisation

A chemical reaction between an acid and a base or alkali to produce salt and water.

Standard solution

A solution with an accurately known concentration.

Molarity

The number of moles of solute present in $1\,dm^3$ of solution.

Salt

An ionic compound formed when the hydrogen ion in an acid is replaced by a metal ion or ammonium ion ($NH_4^+$).

SNAP salts

Salts containing Sodium, Nitrate, Ammonium, or Potassium, all of which are always soluble in water.

Preparation of insoluble salts

Double decomposition reaction (precipitation reaction) using two soluble salt solutions.

Reaction between lead(II) nitrate and potassium iodide

Forms a yellow precipitate of lead(II) iodide ($PbI_2$).

Limewater test for carbon dioxide

Gas turns limewater chalky due to the formation of a white precipitate of calcium carbonate ($CaCO_3$).

Chemical test for sulphate ions ($SO_4^{2-}$)

Add dilute hydrochloric acid ($HCl$) followed by barium chloride ($BaCl_2$) solution; a white precipitate forms.

Chemical test for chloride ions ($Cl^-$)

Add dilute nitric acid ($HNO_3$) followed by silver nitrate ($AgNO_3$) solution; a white precipitate forms.