Required Practical 13: Water Purification

About this practical...

In these experiments, you will have samples of water which you will test the pH and compare with drinking water. You will then evaporate some of the samples of water to see if there are any solid crystals left behind showing that there were dissolved solids. Finally, you get to carefully purify a sample through distillation.


Method 1: Analysis of water samples

1. Using universal indicator, test and record the pH of all of the available water samples.

2. Using a measuring cylinder, accurately measure out 25 cm3 of the first sample.

3. Weigh an evaporating basin and record the mass

4. Add the water sample then heat with a Bunsen. It is important to stop heating while there is still a small amount of water left.

5. Leave the evaporating basin to cool and the rest of the water to evaporate.

6. Reweigh the basin, record the new mass and calculate the mass of dissolved solids in the sample.

Method 2: Purifying a sample of water using distillation

1. Carefully setup the distillation equipment as shown by your teacher

2. Before heating the impure water, check that all of the glassware is stable.

3. Heat the water until it is boiling and collect at least 1 cm of water in the collection tube.

4. Stop heating the sample and allow it to cool.

5. Gently clamp the boiling tube with your pure water at a slight angle and add a thermometer

6. Heat the sample until it boils, if it is pure water, its boiling point should be exactly 100°C

Throughout this second method, be aware that lots of equipment gets hot, please take care and wait for it to cool.

Safety & Managing Risks

Usual lab rules must be followed: loose hair tied back, goggles worn throughout the lesson, bags and stools tucked away and notify the teacher of any spills or breakages immediately. Take care when using the Bunsen. It is crucial that you do not boil the solution dry in the evaporation dish as it will spit and hot crystals will potentially land on people. For more detailed information, please consult CLEAPSS.

Technician notes:

4 large bottles of water - samples A to D

The 4 bottles have different pH levels and different amounts of dissolved salt

Universal indicator

Test tubes

Evaporating basins


Distillation equipment - boiling tube, bung and delivery tube

This page was updated on: 8th January 2022