1.
Which of the following is needed for the combustion of substances?
Correct Answer
C. Oxygen
Explanation
Oxygen is needed for the combustion of substances because it is a highly reactive gas that supports the chemical reaction of burning. During combustion, oxygen molecules react with the fuel molecules, breaking their chemical bonds and releasing energy in the form of heat and light. Without oxygen, combustion cannot occur as there would be no source of oxygen atoms to combine with the fuel molecules. Nitrogen, carbon dioxide, and noble gases do not play a direct role in the combustion process.
2.
Car exhausts are a major source of pollution by nitrogen oxides. Which statement explains how the oxides are produced?
Correct Answer
C. Heat from the engine makes atmospHeric nitrogen and oxygen react together
Explanation
The correct answer is "Heat from the engine makes atmospheric nitrogen and oxygen react together." When the engine of a car heats up, it causes the atmospheric nitrogen and oxygen to react and form nitrogen oxides. This reaction occurs due to the high temperatures reached during combustion in the engine.
3.
Carbon monoxide is a pollutant emitted from the car exhaust system. Which of the following reasons explain why carbon monoxide is considered as an air pollutant?
Correct Answer
D. It causes breathing difficulties by preventing the absorption of oxygen
Explanation
Carbon monoxide is considered an air pollutant because it causes breathing difficulties by preventing the absorption of oxygen. This is because carbon monoxide has a higher affinity for hemoglobin in the blood than oxygen, leading to a decrease in the amount of oxygen that can be transported to the body's tissues. This can result in symptoms such as shortness of breath, dizziness, and even death in severe cases.
4.
Which of the following substances is not found in a clean air sample?
Correct Answer
C. Hydrogen
Explanation
Air is made up of nitrogen, oxygen, carbon dioxide and noble gases.
Helium is a noble gas. Hydrogen does not belong to any of these categories.
5.
Which of the following processes will not affect the carbon cycle?
Correct Answer
D. Neutralisation
Explanation
Photosynthesis removes carbon dioxide in the atmosphere.
Both respiration and combustion adds carbon dioxide to the atmosphere.
Neutralisation does not affect the carbon cycle.
6.
120 cm3 of air is heated with phosphorus to form phosphorus (V) oxide in the air. After the reaction, what is the volume of air which remained?
Correct Answer
C. 96
Explanation
The oxygen has reacted with phosphorus.
There is 20% of oxygen in the composition of air,
Amount of oxygen reacted: 20% of 120 = 24
Remaining volume of air: 120 - 24 = 96
7.
The burning of fossil fuels releases an air pollutant which attacks limestone and buildings. Which of the following is the air pollutant released?
Correct Answer
D. Sulfur dioxide
Explanation
Both sulfur dioxide and oxides of nitrogen causes acid rain which corrodes buildings.
However, only sulfur dioxide is produced from the burning of fossil fuels.
8.
Unpolluted rain water has a pH of about 6. Which of the following gas causes this pH?
Correct Answer
A. Carbon dioxide
Explanation
pH 6 is slightly acidic.
Carbon dioxide dissolves in water to form carbonic acid, which is slightly acidic.
CO2 + H2O --> H2CO3
Nitrogen dioxide dissolves to form nitric acid while sulfur dioxide dissolves to form sulfuric acid, with a pH of about 3.
9.
Which gas is not produced when hydrocarbons are burnt in the internal combustion engines?
Correct Answer
C. Hydrogen
Explanation
Complete combustion produces H2O and CO2.
Incomplete combustion produces CO.
Oxides of nitrogen are produced around the engines at high temperatures. N2 + 2O2 + heat --> 2NO2
Hydrogen is not produced.
10.
A tyre of a lorry is made by heating together a mixture of sulfur and rubber. Rubber is a hydrocarbon. What are the products if the tyre is completely burnt in air?
Correct Answer
C. Carbon dioxide, sulfur dioxide, water
Explanation
Sulfur reacts with oxygen to form sulfur dioxide.
S (g) + O2 (g) --> 2SO2 (g)
Hydrocarbon burns completely to form carbon dioxide and water.