Water Purification Virtual Lab: Analyze and Distill Water

Updated 2026-10-07

This water purification virtual lab matches the AQA GCSE Chemistry required practical on analyzing and purifying water samples from different sources. Students measure the pH of tap, sea, rain and river water and filter off any mud. They then evaporate a known volume in a weighed basin to find the mass of dissolved solids in g/dm³. Finally they distill a sample and test the distillate: its pH, its boiling point and whether it leaves a residue. Every weighing appears on a balance, so students do the calculation themselves. They can also set up the condenser or thermometer wrongly and see what goes wrong.

Water analysis – pH, dissolved solids and distillation

Curriculum links

AQA GCSE Chemistry 4.10.1.2 (potable water) and its required practical: analysis and purification of water samples, including pH, mass of dissolved solids and distillation. The same practical appears in AQA GCSE Combined Science: Trilogy.

Simulic is not affiliated with or endorsed by AQA.

Before the lab (5 min)

Ask students to commit to a prediction:

"You distill sea water, which holds about 35 g of dissolved solids per dm³. How much dissolved solid will the distillate contain?"

Some students expect salt to travel with the steam. Leave the question open.

Method in the simulation

Set Sample to Sea water, Volume evaporated to 50 cm³, tick Filter before evaporating, Balance 0.01 g and Setup correct.
Follow the numbered buttons: measure the pH, filter, weigh the empty basin (m₁), add the sample, evaporate, then weigh again (m₂). Calculate the dissolved solids = (m₂ − m₁) ÷ volume in dm³.
Distill 100 cm³ of sample. Watch the flask temperature and the side-arm thermometer, collect at least 20 cm³, then turn off the heat.
Test the distillate: pH, boiling point and residue after evaporating.
Repeat for tap, rain and river water. For river water, use 100 cm³ and the 0.001 g balance, then run it once filtered and once unfiltered.
Try Setup: thermometer in the liquid, and cooling water in at the top.

Sample	Filtered?	V (cm³)
Sea	yes	50
Tap	yes	100
Rain	yes	100
River	yes	100
River	no	100

Expected results

Readings from the simulation (pH by meter; the indicator rounds to whole numbers):

Sample	pH	Dissolved solids (g/dm³)
Sea	8.1	35.0 (residue 1.75 g from 50 cm³)
Tap	7.4	0.300
River, filtered	7.0	0.200
River, unfiltered	7.0	0.350
Rain	5.6	0.010 (residue only 0.001 g)

Sea water has by far the most dissolved solids. Muddy river water has less dissolved solid than tap water once it is filtered. The mud is suspended, not dissolved.
Filtering removes the 0.15 g/dm³ of silt from river water but nothing from sea water: salt passes through filter paper.
Rain water is acidic (pH 5.6) from dissolved CO₂, yet it has almost no solids. Its residue is close to the balance resolution, so the result is very uncertain.
During distillation, sea water in the flask boils at 100.5 °C. It reaches 101.5 °C as it concentrates, while the side-arm thermometer reads 100.0 °C.
The distillate has pH 7.0 (meter 6.9–7.1), boils at exactly 100.0 °C and leaves 0.00 g of residue.
With the thermometer bulb in the liquid, it reads 101.4 °C instead of the vapor temperature. With the cooling water in at the top, steam escapes and the auto run collects 29 cm³ instead of 53 cm³.

Questions for students

(Prediction, asked again after the lab) How much dissolved solid will the distillate of sea water contain?
Which variable must be controlled when you compare dissolved solids in different samples?
What is the mass of dissolved solids in sea water, in g/dm³?
From two river-water runs, what is the mass of suspended solids per dm³?
Which results show that the distillate is pure water, and why does distillation work?

Answers for teachers: (1) Almost none: 0.00 g of residue. (2) Whether the sample is filtered before evaporating. (3) 35.0 g/dm³ (accept 34.6–35.4). (4) 0.35 − 0.20 = 0.15 g/dm³ (accept 0.13–0.17). (5) pH 7, a constant boiling point of 100.0 °C and no residue. Water boils off and condenses, and the dissolved solids stay behind in the flask.

Common misconceptions

"Cloudy water has the most dissolved solids." Cloudiness is suspended silt. Filtered river water has less dissolved solid than tap water.
"Filtering makes water pure." Filter paper only removes insoluble particles. Dissolved salts pass straight through.
"Clean water must be neutral." Rain water is almost solid-free but has pH 5.6.
"Potable water is pure water." Tap water is safe to drink but still leaves 0.300 g/dm³ of dissolved salts.

Extension

Unknown sample: choose Unknown sample and identify it from its pH and dissolved solids. It could be brackish estuary water, mineral water, an acidic peat stream or pond water.
Precision: evaporate 10 cm³ of tap water on the 0.01 g balance, then 100 cm³ on the 0.001 g balance. Ask why the first result is nearly useless.

FAQ

Are the results the same for every student?

For the four known samples, yes, apart from balance rounding of about ±0.01 g. That's why questions 3 and 4 accept a small range. Only the Unknown sample is random.

Why evaporate on a water bath?

A water bath heats gently, so the residue doesn't spit out of the basin. The simulation does the same.

Why does the flask temperature rise above 100 °C?

Dissolved solids raise the boiling point of the solution. As water boils off, the solution gets more concentrated, so its boiling point slowly rises. The vapor reaching the side arm is pure water at 100 °C.