Quick answer: Air is about 78 % nitrogen and 21 % oxygen. This Chemistry 9-10 lab on atmosphere and Earth resources gives the aim, the equipment, the safety points, a step-by-step method, sample results and 8 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
Fresh water is scarce, and many countries must clean polluted or salty water. In this lab you treat a muddy salt solution in two stages, filtration and distillation, then use mass measurements and a chemical test to show what each stage removes and what it leaves behind.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-ESS3-6, GCSE C9-C10
Aim
To make clean water from a muddy salty sample by filtration and distillation, and to measure how much solid is removed at each stage.
Equipment
- sample A (soil and salt stirred in water), filter funnel and paper, beakers
- conical flask with bung and delivery tube, test tube, beaker of cold water, heat source and tripod
- 25 cm³ measuring cylinder, evaporating dishes, balance (±0.001 g)
- dilute nitric acid, dilute silver nitrate solution, goggles
Safety
Wear goggles. Silver nitrate stains skin and is harmful; dilute nitric acid is irritant. Never heat the flask until it is dry, and remove the delivery tube from the collecting tube before the heat is turned off. Hot steam can scald.
Method
- Measure 25 cm³ of sample A into a weighed evaporating dish, heat it gently until dry, cool it and reweigh. Record the mass of solid.
- Filter the rest of sample A to make sample B. Repeat step 1 with 25 cm³ of B.
- Distil about 50 cm³ of B and collect the liquid as sample C. Repeat step 1 with 25 cm³ of C.
- Put 2 cm³ of each sample in a test tube, add 3 drops of dilute nitric acid and 3 drops of silver nitrate. Record what you see.
Results
The class results were:
| Sample | Appearance | Silver nitrate test | Solid left from 25 cm³ (g) |
|---|---|---|---|
| A original | brown, muddy | heavy white precipitate | 1.075 |
| B filtered | clear, pale | heavy white precipitate | 0.875 |
| C distillate | clear, colourless | no precipitate | 0.000 |
Analysis questions
Question 1 Dissolved solids
Calculate the concentration of dissolved solids in sample B in g/dm³.Question 2 Mud removed
Calculate the mass of mud in 25 cm³ of A and in 1 dm³ of A.Question 3 Fraction of solid that is mud
Calculate the percentage of the total solid in A that is mud.Question 4 Why filtering is not enough
Explain why filtration cannot make sample A drinkable.Question 5 Silver nitrate test
Name the ion detected, give the ionic equation, and explain the result for sample C.Question 6 Chloride concentration
Sample B contains sodium chloride only (M = 58.5 g/mol). Calculate the concentration in mol/dm³.Question 7 Role of the cold water
Explain the roles of the cold water bath and of not heating to dryness.Question 8 Evaluate the method
Distilled water is not what is supplied to homes. Give two reasons and one improvement to the lab.
