Water Purification GCSE Chemistry Practical

Analysing and purifying a sample of water and making it
‘safe to drink’.

During this required practical, students are required to test, analyse, and purify a water sample using a simple distillation. The students will measure the pH of the water, comparing it with the pH of pure water and will reveal and remove any dissolved solids by evaporation. They will then distill the water and re-test it to show it is now purified. Their use of laboratory equipment is also assessed.

Equipment

• Safety goggles
• Bunsen burner
• Tripod
• Gauze
• Heatproof mat
• Test tubes
• Test tube rack
• Evaporating basin
• 50ml measuring cylinder

• 100ml conical flask
• Rubber bung with one hole and delivery tube
• Retort stand and clamp
• Crystallising dish
• Full range universal indicator solution
• Full range universal indicator paper
• Water samples

Equipment for the class to share

• Electronic balance (2 decimal place)
• CLEAPSS Hazcards: 47A, 95A

Method

Activity 1: Analysing a Water Sample

Collect Equipment

Gather all necessary equipment, including a Bunsen burner, evaporating basin, electronic balance, universal indicator paper, and water samples.

Test the pH of the Water Samples

Use a piece of universal indicator paper to test the pH of each water sample.
Record the pH values in a suitable table.

Weigh the Evaporating Basin

Use the electronic balance to weigh an empty evaporating basin.
Record the mass to two decimal places.

Add Water to the Basin

Pour 10ml of the first water sample into the evaporating basin.
Record the combined mass of the evaporating basin and the water.

Heat the Water Sample

Place the evaporating basin over the Bunsen burner.
Heat gently until dissolved solids begin to appear as the water evaporates.

Cool and Weigh the Solids

Once most of the water has evaporated, turn off the Bunsen burner and allow the basin to cool.
Re-weigh the evaporating basin with the remaining solids and record the mass.

Repeat for All Water Samples

Repeat Steps 3–6 for each water sample, recording results in the table.

Activity 2: Purifying Water by Distillation

Set Up the Distillation Equipment

Assemble the distillation apparatus:

Place a conical flask on a tripod and gauze over a Bunsen burner.
Add 10ml of the first water sample to the conical flask.
Insert a bung with a delivery tube into the flask, ensuring the other end of the tube extends 3cm above the bottom of a test tube.
Place the test tube in a beaker of iced water and secure it with a retort stand and clamp.

Heat the Water Sample

Gently heat the conical flask until the water starts to boil.
Lower the heat to maintain a gentle boil.

Observe the Distillation Process

Watch as steam rises in the conical flask, condenses on the inside of the delivery tube, and collects as purified water in the test tube.
Continue distillation until approximately 1cm of water is collected in the test tube.

Turn Off the Equipment

Switch off the Bunsen burner once the desired amount of purified water has been collected.

Analyse the Distilled Water

Determine the boiling point of the distilled water to confirm its purity.

Technician tips

• The pH of a water sample could be increased using Hydrochloric Acid.
• Dissolved solids could include Sodium Chloride and Sodium Carbonate.
• To prevent suck-back during the distillation, students should be warned to not let the solution from the conical flask boil into the delivery tube. The end of the delivery tube should be kept at least 3cm away from the bottom of the test tube.