C8 - Titration

• A titration is a practical technique in which an acid and an alkali are reacted together. The volume of one solution needed to neutralise a set volume of the other solution is carefully measured.

• A titration involves the use of a pipette and burette to accurately measure the volumes of the solutions.

• An indicator must be used to determine the exact volume of solution required for neutralisation.

The process of carrying out a titration allows us to accurately measure the volumes of an acid and an alkali required for neutralisation.

An indicator will be used to determine the exact volume required for neutralisation.

In titration you will attempt to work out the exact volume of sodium hydroxide solution required to neutralise 25 cm³ of sulfuric acid.

In order to carry out this practical you will be using two pieces of volumetric apparatus, the pipette and the burette.

You should aim to carry out the experiment with a high degree of accuracy so the correct volume can be determined.

• Sodium hydroxide solution (100 cm³)

• Sulfuric acid (100 cm³)

• Phenolphthalein indicator

• 25.0 cm³ pipette and filler

• 50.0 cm³ burette, retort stand and burette clamp

• Small funnel

• 250 cm³ conical flask (x3)

• Distilled water

• White tile

1. Rinse the burette with distilled water, then with the supplied alkali. Fill the burette with the alkali taking care to ensure that the bottom of the meniscus is on zero and that the jet of the burette is filled completely.

2. Rinse the pipette with distilled water, then with the sulfuric acid. Fill the pipette with the acid, taking care with the pipette filler and ensuring that the bottom of the meniscus is on the ‘line’ of the pipette.

3. Carefully transfer the acid in the pipette into a conical flask, to remove the final drop from the pipette, gently touch the end of the pipette onto the surface of the liquid in the conical flask.

4. Add 3 drops of phenolphthalein indicator to the conical flask and swirl gently to mix.

5. Place the conical flask onto a white tile underneath the burette.

6. Titrate the alkali with the acid, stop adding the alkali when the indicator turns pink and remains pink.

7. Record your ‘rough’ titre value in the results table.

8. Repeat the process with fresh acid and indicator, adding the alkali dropwise with swirling as the end point is reached.

9. Repeat once more, or until 2 titre values are within 0.2 cm³ of each other.

10. Calculate the average titre.

Average titre = _________________cm³

To ensure accuracy in a titration:

• Read volumes from the bottom of the meniscus.

• Add the solution from the burette drop-by-drop near the end point.

• Swirl the conical flask during the titration to ensure the solutions are mixed.

To ensure reliability in a titration:

• Carry out at least two accurate titrations and calculate an average titre.