Separating a sand, salt and water mixture and finding its percentage composition

The idea

A heterogeneous mixture is separated by physical properties (particle size, solubility, boiling point) and the recovered masses give the percentage composition by mass.

What you need

• Prepared mixture of about 2.0 g sand, 2.0 g sodium chloride and 30 mL water in a labelled 100 mL beaker (teacher-weighed masses recorded but not shown to the learner)
• Electronic balance reading to 0.01 g
• Filter funnel, filter paper (Whatman grade 1 or equivalent), 100 mL conical flask
• Evaporating basin, tripod, gauze mat, Bunsen burner or hotplate
• Glass stirring rod, wash bottle of deionised water
• Drying oven or a second hotplate setting for the sand

How to do it

1. Weigh the empty filter paper and the empty evaporating basin; record both masses to 0.01 g.
2. Stir the mixture for one minute so the salt dissolves fully, then filter it; rinse the sand on the paper with 10 mL deionised water so no salt stays behind.
3. Dry the sand and paper (oven at 60 to 80 degrees Celsius for 20 minutes or warm on the hotplate), cool and weigh; repeat drying until two masses agree within 0.02 g.
4. Evaporate the filtrate in the basin over a low flame until crystals appear and only a little liquid is left, then remove the flame and let the hot basin finish the evaporation so the salt does not spit. Cool and weigh; dry again on a low heat or in the oven until the mass is constant.
5. Calculate the mass of sand and of salt recovered, the total, and each as a percentage of the total recovered mass.
6. Compare with the teacher's prepared masses and account for any loss; repeat with a second mixture if time allows.

What you should see

If the teacher weighed out 2.00 g of sand and 2.00 g of salt, the true composition of the dry solids is 50.0 percent sand and 50.0 percent salt by mass. The learner recovers slightly less than 2.00 g of each because some solid stays on the filter paper and the glassware, so the recovered total falls a little short of 4.00 g and the comparison with the teacher's masses shows where the losses occurred. Water is the component removed by evaporation and is not recovered.

What changes

What you change

separation technique used for each component (filtration, evaporation)

What you measure

mass recovered for each component (g)

What you keep the same

• starting masses of each component
• rinse volume
• drying to constant mass

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• Dissolving is a chemical change (it is physical; the salt is recovered unchanged).
• Filtering removes dissolved substances (only insoluble particles are trapped).
• Mass is lost when salt dissolves (the dissolved salt is still there and is recovered on evaporation).

Safety card

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document)CH11-8CH11/12-3CH11/12-4
• Chemistry 11-12 Syllabus (2025), NESA; implemented from 2028, not yet taughtCH-11-01CH-11WS-03
• Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

1. www.nsw.gov.au/education-and-training/nesa/curriculum/science/chemistry-stage-6-2017
2. www.nsw.gov.au/sites/default/files/noindex/2025-03/chemistry-stage6-syllabus-word.docx
3. curriculum.nsw.edu.au/learning-areas/science/chemistry-11-12-2025/outcomes
4. edu.rsc.org/resources/separating-mixtures/499.article
5. edu.rsc.org/cpd/separation-techniques/3009787.article
6. education.nsw.gov.au/content/dam/main-education/teaching-and-learning/curriculum/key-learning-areas/science/s-6/chemistry/Chemistry-module-1-guide.docx