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AQA GCSE · Question 09.3 · Chemical changes

A student does a titration to find the volume of acid needed to neutralise an alkali.
The student fills a burette with the acid.
Give three more steps the student must do before adding the acid to the alkali from the burette.
You should name any equipment used.

How to approach this question

Think about the standard titration procedure. The acid is in the burette. 1. **The Alkali:** How do you accurately measure a specific volume of the alkali solution? What piece of equipment is used for this? 2. **The Reaction Vessel:** Where do you put the alkali for the reaction? What is the name of the flask used in titrations? 3. **Detecting the End Point:** How will you know when the alkali has been exactly neutralised? What must be added to the flask to see a colour change?

Full Answer

Before starting to add the acid from the burette, the alkali must be prepared in the reaction vessel. The standard procedure is: 1. **Measure the alkali:** A pipette is used to accurately measure a fixed volume of the alkali (e.g., 25.0 cm³). A pipette filler is used for safety to draw the liquid into the pipette. 2. **Transfer to flask:** The measured volume of alkali is then transferred from the pipette into a conical flask. A conical flask is used because its shape reduces the risk of splashing during the titration. 3. **Add indicator:** A few drops of a suitable acid-base indicator, such as phenolphthalein or methyl orange, are added to the alkali in the conical flask. The indicator will change colour sharply at the end point of the titration, signalling that neutralisation is complete.

Common mistakes

✗ Naming the wrong equipment (e.g., "measuring cylinder" instead of "pipette" for measuring the alkali). ✗ Forgetting to mention the indicator. ✗ Saying "put the alkali in a beaker" - a conical flask is the correct equipment.

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