Quick answer: Air is about 78 % nitrogen and 21 % oxygen. These answers go with the Chemistry 9-10 lab on atmosphere and Earth resources: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
Here are the atmosphere and Earth resources lab answers for chemistry grades 9-10: graph, calculations, uncertainties and conclusion. First do the lab yourself, then compare, and go back to the lesson if needed.
These model answers use the sample data to calculate concentrations and show what each treatment removes. Check your units carefully when converting between cm³ and dm³, and make sure ionic equations balance in charge.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-ESS3-6, GCSE C9-C10
Mud = 1.075 − 0.875 = 0.200 g in 25 cm³. In 1 dm³: 0.200 ÷ 0.025 = 8.0 g.
Question 3 Fraction of solid that is mud
0.200 ÷ 1.075 × 100 = 18.6 % (about 19 %).
Question 4 Why filtering is not enough
Filtration only removes insoluble solids such as soil. Dissolved salt ions are far smaller than the holes in the paper, so they pass through, and the silver nitrate test still gives a precipitate.
Question 5 Silver nitrate test
The ion is chloride. Ag⁺(aq) + Cl⁻(aq) → AgCl(s). Sample C gives no precipitate because the salt stays behind in the flask and the distillate has no chloride ions.
Question 6 Chloride concentration
35 ÷ 58.5 = 0.60 mol/dm³.
Question 7 Role of the cold water
Cold water condenses the steam back to liquid. Heating to dryness could crack the flask and would carry spray or salt over into the distillate.
Question 8 Evaluate the method
Distillation needs a lot of energy, and distilled water lacks the minerals that make water pleasant. Improve the lab by using a condenser and repeating the measurements to give a mean.
