Core practical: acid-alkali titration

1. Use a pipette and pipette filler to put exactly 25.0 cm³ of alkali (for example sodium hydroxide solution) into a conical flask.
2. Add a few drops of indicator (such as phenolphthalein or methyl orange) and stand the flask on a white tile.
3. Rinse the burette with a little of the acid, then fill it with acid using a small funnel, with the burette below eye level. Remove the funnel and run a little acid through so the tip has no air bubbles. Record the starting reading.
4. Rough titration: add acid while swirling the flask until the indicator changes colour. This gives an idea of the volume needed.
5. Accurate titrations: wash out the flask with distilled water, then add a fresh 25.0 cm³ of alkali and indicator. Add acid quickly to about 2 cm³ before the rough end point, then drop by drop, swirling, until the colour just changes. Record the final reading.
6. Titre = final reading − starting reading. Repeat until you have concordant results.
Safety: wear eye protection, because acids and alkalis can damage the eyes and skin.

Phenolphthalein: pink in alkali, colourless in acid.
Methyl orange: yellow in alkali, red in acid.
These change colour sharply at the end point. Universal indicator is not used, because it changes colour gradually through many colours, so there is no clear end point.
The white tile makes the colour change easy to see.

Read the burette at eye level, from the bottom of the meniscus, to the nearest 0.05 cm³ (so readings have two decimal places, such as 23.45 cm³).
Concordant results are titres within 0.10 cm³ of each other. Calculate the mean of the concordant titres only. Leave out the rough titre, because it usually overshoots the end point.
Higher tier: use the mean titre to calculate an unknown concentration. Moles of acid = concentration × volume in dm³, then use the ratio in the balanced equation.