10.1 Water
1. Describe the chemical test for the presence of water using anhydrous cobalt(II) chloride.
Anhydrous cobalt(II) chloride turns from blue to pink in the presence of water.
2. Describe the chemical test for the presence of water using anhydrous copper(II) sulfate.
Anhydrous copper(II) sulfate turns from white to blue in the presence of water.
3. How is the purity of water tested using physical properties?
By checking its melting point and boiling point; pure water has a fixed melting point of 0 °C and a boiling point of 100 °C.
4. Why is distilled water preferred over tap water in practical chemistry?
Because distilled water contains fewer chemical impurities.
5. List the specific substances that may be found in water from natural sources.
Dissolved oxygen, metal compounds, plastics, sewage, harmful microbes, nitrates (from fertilisers), and phosphates (from fertilisers and detergents).
6. Which substances in natural water are considered beneficial, and why?
Dissolved oxygen is beneficial for aquatic life, and some metal compounds provide essential minerals for life.
7. What are the potentially harmful effects of metal compounds and plastics in water?
Some metal compounds are toxic, and some plastics harm aquatic life.
8. What is the danger of sewage in water supplies?
Sewage contains harmful microbes which cause disease.
9. What are the environmental consequences of nitrates and phosphates in water?
They lead to the deoxygenation of water and damage to aquatic life.
10. Describe the two steps in domestic water treatment used to remove solids.
Sedimentation and filtration.
11. What is the purpose of using carbon in water treatment?
To remove unpleasant tastes and odours.
12. Why is chlorination used in the treatment of the domestic water supply?
To kill harmful microbes.
10.2 Fertilisers
13. Name the two types of salts used as fertilisers mentioned in the syllabus.
Ammonium salts and nitrates.
14. What are NPK fertilisers?
Fertilisers that provide the elements nitrogen (N), phosphorus (P), and potassium (K).
15. Why are NPK fertilisers used in agriculture?
To provide essential elements for improved plant growth.
10.3 Air quality and climate
16. State the approximate percentages of the primary gases in clean, dry air.
Approximately 78% nitrogen (N2), 21% oxygen (O2), and the remainder as a mixture of noble gases and carbon dioxide (CO2).
17. What is the source of carbon dioxide as an air pollutant?
The complete combustion of carbon-containing fuels.
18. State the sources of carbon monoxide and particulates.
The incomplete combustion of carbon-containing fuels.
19. What are the sources of methane in the atmosphere?
The decomposition of vegetation and waste gases from digestion in animals.
20. How are oxides of nitrogen formed?
They are formed in car engines.
21. What is the source of sulfur dioxide?
The combustion of fossil fuels which contain sulfur compounds.
22. Describe the adverse effect of increased carbon dioxide levels.
Increased levels lead to increased global warming, which causes climate change.
23. Why is carbon monoxide considered a pollutant?
It is a toxic gas.
24. What are the health risks associated with particulates?
An increased risk of respiratory problems and cancer.
25. Describe the adverse effect of increased methane levels.
Higher levels lead to increased global warming and subsequent climate change.
26. What are the three adverse effects of oxides of nitrogen?
Acid rain, photochemical smog, and respiratory problems.
27. State the adverse effect of sulfur dioxide.
It causes acid rain.
28. Explain how greenhouse gases like carbon dioxide and methane cause global warming.
They absorb, reflect, and emit thermal energy, thereby reducing thermal energy loss to space.
29. List five strategies to reduce the effects of climate change.
Planting trees, reduction in livestock farming, decreasing use of fossil fuels, increasing use of hydrogen, and increasing use of renewable energy (e.g., wind, solar).
30. List three strategies to reduce the effects of acid rain.
Use of catalytic converters in vehicles, using low-sulfur fuels, and flue gas desulfurisation with calcium oxide.
31. Define photosynthesis.
The reaction between carbon dioxide and water to produce glucose and oxygen in the presence of chlorophyll and using energy from light.
32. State the word equation for photosynthesis.
carbon dioxide + water → glucose + oxygen
33. State the symbol equation for photosynthesis.
6CO2 + 6H2O → C6H12O6 + 6O2
34. How do oxides of nitrogen form in car engines?
Nitrogen and oxygen from the air react together due to the high temperatures inside the engine.
35. Describe how catalytic converters remove pollutants from car exhausts.
They facilitate a reaction between carbon monoxide and nitrogen monoxide to produce nitrogen and carbon dioxide.
36. State the symbol equation for the reaction occurring in a catalytic converter.
2CO + 2NO → 2CO2 + N2