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Titrations are a very accurate experimental technique used to find volumes of acid and alkali solutions that react together.

Before a titration is carried out the apparatus should be prepared.

1. A pipette should be rinsed with deionised water and then with the solution which is it is going to be used to measure.
2. A safety pipette filler should be used to draw up the solution until the bottom of the meniscus is on the line and the solution is then released into a conical flask.
3. A burette is rinsed with deionised water and then with the solution which is going to be used in the burette, ensuring the solution passes through the jet.
4. The burette is then filled with the solution, ensuring the jet is filled.

Method

This method is for titrating an acid into an alkali. The method is the same for sulfuric acid, hydrochloric acid and nitric acid.

1. Use the pipette and pipette filler to add a measured volume of sodium hydroxide solution to a clean conical flask.
2. Add a few drops of indicator and put the conical flask on a white tile.
3. Fill the burette with hydrochloric acid and note the initial reading.
4. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix. Add the acid drop by drop toward the end for maximum accuracy.
5. Stop adding the acid when the indicator first permanently changes colour (the end point). Note the final reading.
6. Repeat steps 1 – 5, until you get concordant (agreeing) titres.

Results

Record the results in a table.

Record your readings to one decimal place. The units must be placed with the quantity in the heading of the column. A reading of 0 cm³ or 24 cm³ on the burette must be recorded to one decimal place as 0.0 cm³ and 24.0 cm³.

The titre is the volume added (the difference between the end and start readings). A rough titration is carried out to get an idea of the end point of the titration so the accurate titration may be carried out more rapidly. The solution in the burette should be added dropwise, whilst swirling the conical flask, as you approach the end point.

Analysis

Concordant titres are within 0.2 cm³ (or sometimes 0.1 cm³) of each other. The results of titrations 1 and 3 are concordant titres.

Worked example

Calculate the average titre from the figures in the table. Ignore the rough run and run 2 – they are not concordant.

Prescribed Practical C8 - Determine the reacting volumes of solutions of acid and alkali by titration and determine the concentration of solutions of acid and alkali by titration