Required Practical: Titration — AQA GCSE Chemistry

This required practical uses titration to find the volume of acid and alkali that exactly react.

Apparatus

• A pipette (and pipette filler) to measure an accurate, fixed volume of one solution into a conical flask.
• A burette to add the other solution gradually, read to the nearest 0.05 cm³.
• A suitable indicator — phenolphthalein (pink in alkali, colourless in acid) or methyl orange (yellow in alkali, red in acid). Universal indicator is not used because it does not give a sharp colour change.

Method

1. Use the pipette to add a measured volume of alkali to the conical flask, and add a few drops of indicator.
2. Fill the burette with acid and record the starting reading.
3. Add the acid slowly, swirling, especially near the end point.
4. Stop when the indicator just changes colour (the end point) and record the final reading.
5. The titre = final − initial reading.
6. Repeat until results are concordant (within 0.10 cm³) and calculate a mean titre.

Improving accuracy

• Do a rough titration first, then accurate ones.
• Swirl the flask and add dropwise near the end point.
• Read the burette at eye level from the bottom of the meniscus.

Exam tips

• Use a pipette (fixed volume) and a burette (read to 0.05 cm³).
• Use a single indicator with a sharp colour change (not universal indicator).
• Repeat for concordant results and use the mean titre.
• Read the burette at eye level (bottom of the meniscus).