A titration finds exactly how much acid neutralises a measured volume of alkali. The skill is in the procedure: pipette, indicator, burette, swirl, and repeat until two titres agree.
In an acid-base titration a volumetric pipette transfers a fixed volume of alkali (for example 25.0 cm3) into a conical flask, a few drops of indicator are added, and acid is run in from a burette until the indicator just changes colour: the end-point. The volume of acid added is the titre (final reading minus initial reading). A rough titre is followed by accurate titrations, adding acid drop by drop near the end-point, until concordant results (titres within 0.10 cm3 of each other) are obtained; their mean is used. Methyl orange is red in acid and yellow in alkali; thymolphthalein is colourless in acid and blue in alkali. Litmus is not used for titrations because its colour change is not sharp.
Run a titration in the simulator: fill the burette, add the indicator, and slow down to single drops as the colour starts to change.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Which piece of apparatus is used to add the acid during a titration?
What colour is methyl orange in an alkali?
Thymolphthalein is added to sodium hydroxide solution, which is then titrated with acid. What is the colour change at the end-point?
What are concordant titres?
Extended. Record readings to 0.05 cm3, pick the concordant titres, then use moles to find the unknown concentration.
| rough | 1 | 2 | 3 | |
|---|---|---|---|---|
| final reading / cm3 | 25.10 | 24.65 | 48.90 | 24.40 |
| initial reading / cm3 | 0.50 | 0.50 | 24.65 | 0.20 |
| titre / cm3 | 24.60 | 24.15 | 24.25 | 24.20 |
The rough titre overshoots the end-point, so leave it out of the mean. Titre = final reading minus initial reading, not the final reading alone. Use the mole ratio from the equation: with H2SO4, moles of NaOH are twice the moles of acid. And convert cm3 to dm3 by dividing by 1000.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
A burette reads 1.20 cm3 at the start and 23.75 cm3 at the end-point. What is the titre?
Titres of 22.40, 22.90, 22.35 and 22.45 cm3 are obtained. What mean titre should be used?
(Extended) 25.0 cm3 of NaOH(aq) needs 20.0 cm3 of 0.100 mol/dm3 HCl. What is the concentration of the NaOH?
Why is litmus not normally used as the indicator in a titration?
This skill is now recorded on your profile. Keep the chain going.