The questions are on the atmosphere and Earth resources test. Take it under real conditions before reading the mark scheme.
Quick answer: Air is about 78 % nitrogen and 21 % oxygen. This mark scheme gives the model answers and the marks for the 8 questions of the Chemistry 9-10 test on atmosphere and Earth resources, from gases in air to life cycle stages, with the equivalent answers to accept.
Use this guide to mark the test out of 20. Give one mark for each correct point, name or formula. Accept any other correct wording, and do not penalise either British or American spelling.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-ESS3-6, GCSE C9-C10
Question 1 Gases in air (3 marks)
a. Nitrogen.b. Oxygen, about 21 %.
c. Argon.
Marking: 1 mark each.
Question 2 Greenhouse effect (3 marks)
a. Carbon dioxide and methane.b. They absorb infrared radiation from the warm surface and send part of it back to the Earth, so less heat escapes to space.
Marking: a. 1 mark. b. 1 mark for absorbing infrared, 1 mark for sending it back.
Question 3 Carbon monoxide (2 marks)
It forms by incomplete combustion when there is not enough oxygen. It is toxic because it binds to haemoglobin and stops the blood carrying oxygen.Marking: 1 mark each.
Question 4 Acid rain (3 marks)
a. Sulfur dioxide.b. Acid rain that damages trees, buildings and lakes.
c. Remove sulfur from the fuel, or use a scrubber on the power station waste gases.
Marking: 1 mark each.
Question 5 Potable water (2 marks)
Potable water is safe to drink but contains dissolved minerals and possibly chlorine. Pure water contains only H₂O.Marking: 1 mark for safe to drink, 1 mark for pure water only H₂O.
Question 6 Water treatment (3 marks)
The water passes through screens, then settling and a sand and gravel filter bed to remove solids. Chlorine is added to kill microbes.Marking: 1 mark for filtering, 1 mark for sterilising, 1 mark for killing microbes.
Question 7 Volume calculation (2 marks)
0.04 ÷ 100 × 250 = 0.10 dm³ (100 cm³).Marking: 1 mark for method, 1 mark for the answer with unit.
Question 8 Life cycle stages (2 marks)
Getting raw materials, manufacturing, use, and disposal.Marking: Half a mark each; 2 marks for all four.
