Reactions of non-metals with oxygen - Natural Science Grade 9 PDF Download

Table of Contents
1. Section A: Multiple Choice
2. Section B: True or False
3. Section C: Match the Column
4. Section D: Fill in the Blanks
5. Section E: Short Questions
6. Section F: Scenario Question
7. Section G: Long Question
8. Answer Key
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Section A: Multiple Choice

Choose the correct answer from the options given.

Question 1
When carbon reacts with oxygen, which product is formed?
A. Carbon monoxide only
B. Carbon dioxide only
C. Carbon dioxide or carbon monoxide depending on the oxygen supply
D. Carbon hydroxide
[2]

Question 2
Thandi burns sulfur in a gas jar containing oxygen. What colour is the flame produced?
A. Yellow
B. Blue
C. Green
D. Red
[2]

Question 3
What type of oxide is formed when phosphorus reacts with oxygen?
A. Basic oxide
B. Neutral oxide
C. Acidic oxide
D. Amphoteric oxide
[2]

Question 4
Which statement best describes the general reaction of non-metals with oxygen?
A. Non-metals react slowly with oxygen at room temperature
B. Non-metals form basic oxides when they react with oxygen
C. Non-metals form acidic oxides when they react with oxygen
D. Non-metals do not react with oxygen under any conditions
[2]

Section B: True or False

State whether each statement is TRUE or FALSE.

Question 1
Sulfur dioxide dissolves in water to form sulfuric acid directly.
[1]

Question 2
Non-metal oxides turn blue litmus paper red when dissolved in water.
[1]

Question 3
Nitrogen reacts vigorously with oxygen at room temperature.
[1]

Question 4
Complete combustion of carbon produces carbon dioxide gas.
[1]

Section C: Match the Column

Match the items in Column A with the correct descriptions in Column B. Write only the letter of your answer next to the question number.

[4]

Section D: Fill in the Blanks

Complete the sentences below using words from the word bank. Use each word only once.

Word Bank: acidic, carbon dioxide, combustion, non-metals

Question 1
The process of burning substances in oxygen is called ________.
[1]

Question 2
When ________ react with oxygen, they typically form acidic oxides.
[1]

Question 3
Complete combustion of carbon in sufficient oxygen produces ________.
[1]

Question 4
Non-metal oxides dissolved in water form ________ solutions.
[1]

Section E: Short Questions

Question 1
Write the word equation for the reaction of sulfur with oxygen.
[2]

Question 2
Explain why sulfur dioxide is considered an air pollutant.
[3]

Question 3
Describe what happens when carbon dioxide gas is bubbled through limewater.
[2]

Question 4
Sipho observes that a piece of charcoal glows more brightly when placed in pure oxygen than in air. Explain why this happens.
[3]

Section F: Scenario Question

Kagiso is conducting an experiment in the science laboratory. She places a small piece of red phosphorus in a deflagrating spoon and heats it until it ignites. She then lowers the burning phosphorus into a gas jar filled with oxygen gas. After the reaction is complete, she carefully adds a small amount of water to the gas jar, covers it with a lid, and shakes it gently. She then tests the solution formed with blue litmus paper.

Question 1
What gas is produced when phosphorus burns in oxygen?
[2]

Question 2
Write a balanced chemical equation for the reaction between phosphorus and oxygen. Use P₄ to represent phosphorus and P₄O₁₀ as the product.
[3]

Question 3
Predict what happens to the blue litmus paper when Kagiso tests the solution.
[2]

Question 4
Explain why the litmus paper changes colour in this way, referring to the nature of the oxide formed.
[3]

Section G: Long Question

Lerato investigates the combustion of carbon under different conditions. She burns charcoal in two separate gas jars: one containing a limited supply of oxygen and another containing excess oxygen. She collects the gases produced in each jar and tests them.

Question 1
Identify the two different products that can form when carbon reacts with oxygen under different conditions, and name the type of combustion that produces each.
[4]

Question 2
Write balanced chemical equations for both reactions described in Question 1.
[4]

Question 3
Lerato bubbles the gas from the excess oxygen jar through limewater and observes that the limewater turns milky. Explain this observation fully, including the chemical reason for the colour change.
[3]

Question 4
Carbon monoxide is a poisonous gas, whereas carbon dioxide is not considered poisonous at normal concentrations. Evaluate why incomplete combustion of carbon-containing fuels in homes is dangerous, and suggest one safety measure to prevent carbon monoxide poisoning.
[4]

Grand Total: [55]

Answer Key

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Section A - Question 1

Answer: C. Carbon dioxide or carbon monoxide depending on the oxygen supply
Carbon can form two different oxides when it reacts with oxygen. If there is plenty of oxygen available, complete combustion occurs and carbon dioxide (CO₂) is formed. If oxygen is limited, incomplete combustion happens and carbon monoxide (CO) is produced instead.

Section A - Question 2

Answer: B. Blue
When sulfur burns in oxygen, it produces a blue flame. This is a characteristic observation that helps identify sulfur combustion in the laboratory.

Section A - Question 3

Answer: C. Acidic oxide
Phosphorus is a non-metal, and non-metals typically form acidic oxides when they react with oxygen. Phosphorus pentoxide (P₄O₁₀) is an acidic oxide that dissolves in water to form phosphoric acid.

Section A - Question 4

Answer: C. Non-metals form acidic oxides when they react with oxygen
This is the key general pattern for non-metal reactions with oxygen. Unlike metals which form basic oxides, non-metals produce acidic oxides that turn blue litmus paper red when dissolved in water.

Section B - Question 1

FALSE
Correction: Sulfur dioxide dissolves in water to form sulfurous acid, not sulfuric acid directly.
Sulfur dioxide (SO₂) reacts with water to produce sulfurous acid (H₂SO₃). Sulfuric acid (H₂SO₄) is formed when sulfur trioxide (SO₃) dissolves in water, or when sulfurous acid is further oxidized.

Section B - Question 2

TRUE
Non-metal oxides dissolve in water to form acidic solutions. Acids turn blue litmus paper red, which is the standard test for acidic substances.

Section B - Question 3

FALSE
Correction: Nitrogen does not react with oxygen at room temperature; it requires very high temperatures such as in lightning or in car engines.
Nitrogen is a very stable molecule (N₂) and does not readily react with oxygen under normal conditions. The reaction only occurs at extremely high temperatures.

Section B - Question 4

TRUE
When carbon undergoes complete combustion in the presence of sufficient oxygen, the product is carbon dioxide gas (CO₂). This is the ideal combustion reaction.

Section C - Match the Column

1. C - Sulfur reacts with oxygen to produce sulfur dioxide (SO₂), which is a pungent-smelling gas that causes acid rain.
2. B - When carbon burns with limited oxygen supply, incomplete combustion occurs and carbon monoxide (CO) is formed, which is a poisonous gas.
3. D - Phosphorus reacts vigorously with oxygen to form phosphorus pentoxide (P₄O₁₀), which is a white powder.
4. A - At very high temperatures, such as during lightning or in vehicle engines, nitrogen reacts with oxygen to form nitrogen dioxide (NO₂), a brown acidic gas.

Section D - Question 1

Answer: combustion
Combustion is the scientific term for burning, which is a chemical reaction between a substance and oxygen that releases heat and light energy.

Section D - Question 2

Answer: non-metals
Non-metals such as sulfur, carbon, phosphorus, and nitrogen react with oxygen to form acidic oxides, which is different from metals that form basic oxides.

Section D - Question 3

Answer: carbon dioxide
Complete combustion means there is enough oxygen for all the carbon to be fully oxidized, producing carbon dioxide (CO₂) rather than carbon monoxide.

Section D - Question 4

Answer: acidic
When non-metal oxides dissolve in water, they form acidic solutions that can be tested with litmus paper or universal indicator.

Section E - Question 1

Model Answer:
Sulfur + Oxygen → Sulfur dioxide [2]
Award 1 mark for correct reactants (sulfur and oxygen) and 1 mark for correct product (sulfur dioxide). The word equation shows the chemical reaction in simple written form.

Section E - Question 2

Model Answer:
Sulfur dioxide is considered an air pollutant because it contributes to the formation of acid rain when it dissolves in atmospheric water [1]. Acid rain damages buildings, harms plant life, and acidifies water bodies [1]. Sulfur dioxide can also cause respiratory problems in humans and animals when inhaled [1].
Award 1 mark for mentioning acid rain, 1 mark for environmental damage, and 1 mark for health effects.

Section E - Question 3

Model Answer:
When carbon dioxide is bubbled through limewater (calcium hydroxide solution), the limewater turns milky or cloudy [1]. This happens because carbon dioxide reacts with calcium hydroxide to form calcium carbonate, which is insoluble and appears as a white precipitate [1].
Award 1 mark for stating the limewater turns milky/cloudy, and 1 mark for explaining that calcium carbonate forms.

Section E - Question 4

Model Answer:
The charcoal glows more brightly in pure oxygen because oxygen is required for combustion [1]. Air contains only about 21% oxygen, while pure oxygen is 100% oxygen [1]. The higher concentration of oxygen in the gas jar allows the combustion reaction to occur much more rapidly and vigorously, releasing more energy as heat and light [1].
Award 1 mark for identifying oxygen is needed for combustion, 1 mark for comparing oxygen concentration in air vs pure oxygen, and 1 mark for explaining the faster/more vigorous reaction.

Section F - Question 1

Model Answer:
The gas produced when phosphorus burns in oxygen is phosphorus pentoxide (or diphosphorus pentoxide) [2].
Award 1 mark for phosphorus oxide and 2 marks for the specific name phosphorus pentoxide. This white solid appears as a powder or smoke during the reaction.

Section F - Question 2

Model Answer:
P₄ + 5O₂ → P₄O₁₀ [3]
Award 1 mark for correct reactants, 1 mark for correct product, and 1 mark for correct balancing. This equation shows that one molecule of phosphorus (containing 4 phosphorus atoms) reacts with five molecules of oxygen gas to produce one molecule of phosphorus pentoxide.

Section F - Question 3

Model Answer:
The blue litmus paper turns red [2].
Award 2 marks for stating the litmus paper turns red. This colour change is the standard test for an acidic solution.

Section F - Question 4

Model Answer:
The litmus paper turns red because phosphorus pentoxide is an acidic oxide [1]. When Kagiso adds water and shakes the jar, the phosphorus pentoxide dissolves in water to form phosphoric acid (H₃PO₄) [1]. Acids turn blue litmus paper red, which confirms the solution is acidic [1].
Award 1 mark for identifying phosphorus pentoxide as an acidic oxide, 1 mark for explaining that it forms phosphoric acid in water, and 1 mark for linking this to the litmus paper colour change.

Section G - Question 1

Model Answer:
The two different products are:
Carbon dioxide (CO₂), which is formed during complete combustion when there is excess or sufficient oxygen [2].
Carbon monoxide (CO), which is formed during incomplete combustion when there is a limited supply of oxygen [2].
Award 1 mark for each product correctly named and 1 mark for each type of combustion correctly identified.

Section G - Question 2

Model Answer:
Complete combustion: C + O₂ → CO₂ [2]
or
2C + O₂ → 2CO₂ [2]
Incomplete combustion: 2C + O₂ → 2CO [2]
Award 2 marks for each correctly balanced equation. Make sure the number of atoms of each element is the same on both sides of the equation.

Section G - Question 3

Model Answer:
The limewater turns milky or cloudy white because carbon dioxide reacts with calcium hydroxide in the limewater [1]. The reaction produces calcium carbonate (CaCO₃), which is insoluble in water [1]. The tiny particles of calcium carbonate suspend in the water, making it appear milky [1].
Award 1 mark for stating the limewater turns milky, 1 mark for identifying that calcium carbonate forms, and 1 mark for explaining that calcium carbonate is insoluble.

Section G - Question 4

Model Answer:
Incomplete combustion of fuels in homes is dangerous because it produces carbon monoxide (CO), which is a poisonous gas [1]. Carbon monoxide binds to haemoglobin in red blood cells more strongly than oxygen does, preventing oxygen from being transported around the body [1]. This can lead to suffocation, unconsciousness, or death [1]. A safety measure to prevent carbon monoxide poisoning is to ensure proper ventilation or install carbon monoxide detectors in the home [1].
Award 1 mark for identifying carbon monoxide as poisonous, 1 mark for explaining its effect on haemoglobin/oxygen transport, 1 mark for mentioning the health consequences, and 1 mark for suggesting a valid safety measure.

Mark Allocation Summary

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