Titration

Aim

To determine the concentration of a strong alkali solution by carrying out a titration with strong acid.

Chemical equation(with sodium hydroxide and hydrochloric acid)

HCl + NaOH → NaCl + H₂O

Molar ratio of HCl to NaOH

1:1

Indicator used

Phenolphthalein — colourless in acid, pink in alkali

Volume of NaOH used

25 cm³

Purpose of the white tile

To make the colour change at the endpoint easier to see

Why the rough titre is excluded from the mean

It is not accurate enough — only concordant results are used

Concordant results

Titres within 0.1 cm³ of each other

How to read the burette

At eye level, from the bottom of the meniscus, to 2 decimal places

Purpose of rinsing pipette with deionised water

To ensure all NaOH is transferred and reacts, improving accuracy

How to calculate moles of HCl

Moles = mean titre volume (dm³) × concentration of HCl

How to calculate concentration of NaOH

Concentration = moles of NaOH ÷ volume of NaOH (dm³)

Sodium hydroxide hazard

Irritant — avoid skin contact, wash immediately if contact occurs

Hydrochloric acid hazard

Corrosive — treat with same precautions as NaOH, wear safety glasses

How to fill the burette safely

Below eye level (e.g. place on the floor) using a funnel

Purpose of the rough titre

To estimate the endpoint so accurate titrations can be done drop by drop near the endpoint

Significant figures for NaOH concentration

3 significant figures

Equipment used to measure NaOH

25 cm³ pipette with pipette filler

Equipment used to deliver HCl

50 cm³ burette

Why the conical flask is rinsed with deionised water between titrations

To remove residue without affecting the moles of NaOH added