Neutralisation & Titrations 3
Chemistry: AQA GCSE Higher, topic 4.3.11
Titrations
Titration is a technique that measures the volumes of acid and alkali solutions that are needed in a neutralisation reaction.
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Method
- Measure a precise volume of unknown solution and place it into a conical flask.
- Add a couple of drops of your indicator. The flask should be placed on a white tile so you can observe any colour change.
- The titre should be added to the burette and the starting point noted.
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Method cont.
- The titre should be added slowly to the unknown solution with swirling.
- No more titre should be added once the indicator permanently changes colour. This should be done dropwise towards the end.
- This is the end-point of the titration and the volume of titre added should be noted.
- Repeat these steps until you obtain concordant results.
Key variables
- If, for example, we were neutralising an alkali with an acid, titration could be used to calculate the concentration of the alkali if we knew:
- The concentration of the acid to be added.
- The volume of the alkali.
Indicators
- Indicators show the end point of titrations by suddenly changing colour when the solution turns from acidic to alkaline, or alkaline to acidic.
Choosing an indicator
- When choosing an indicator, the strength of the acid and alkali must be considered.
- If both the acid and alkali are strong, suitable indicators would be:
- Methyl orange (yellow in alkali → red in acid).
- Phenolphthalein (pink in alkali → colourless in acid).
Test yourself on Neutralisation & Titrations 3
Why do you repeat titrations to obtain multiple results?
Why is the titre added dropwise as you approach the end-point of a titration?
What should be recorded at the end-point of the titration?
Select the true statement in each pair
Why can indicators be used to identify a titration's end-point?