Topic 9Reactions

of Acids

Titrations

Burette with acid solution e.g. dilute hydrochloric acid HCl(aq)

Alkali solution e.g. sodium hydroxide NaOH(aq) + indicator

White tile

We use the following formula:Pacid x Vacid x Cacid = Palkali x Valkali x Calkali

Where P= powerV= volume (l)C=Concentration

• Power of the acid is the number of H+ ions in the formulaHCl has a power of 1HNO3 has a power of 1H2SO4 has a power of 2

• Power of the alkali is the number of OH- ions in the formulaNaOH has a power of 1Mg(OH)2 has a power of 2

Example 1Q. In a titration, 25cm3 of 0.1 mol/l NaOH

was exactly neutralised by 22.2cm3 of hydrochloric acid. Calculate the concentration of the hydrochloric acid.

A. Pacid x Vacid x Cacid = Palkali x Valkali x

Calkali

Cacid = Palkali x Valkali x Calkali

Pacid x Vacid

Cacid = Palkali x Valkali x Calkali

Pacid x Vacid

Cacid= 1 x 0.025 x 0.1 1 x 0.0222

Cacid= 0.11mol/l

Therefore the concentration of acid is 0.11mol/l.

Example 2Q. What volume of 0.2mol/l sulphuric acid

will exactly neutralise 25.0cm3 of 0.5 mol/l potassium hydroxide?

A. Pacid x Vacid x Cacid = Palkali x Valkali x

Calkali

Vacid = Palkali x Valkali x Calkali

Pacid x Cacid

Vacid = Palkali x Valkali x Calkali

Pacid x Cacid

Vacid = 1 x 0.025 x 0.5

2 x 0.2

Vacid =0.03125l

Therefore 31.25cm3 will neutralise the alkali.