- Reactions of non-metals with oxygen Important Questions - Grade 9 PDF

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
View more

Section A: Multiple Choice

1. When carbon burns in oxygen, which gas is produced?

• A. Hydrogen gas
• B. Carbon dioxide
• C. Nitrogen gas
• D. Chlorine gas

[1]

2. What type of solution is formed when sulfur dioxide dissolves in water?

• A. Neutral solution
• B. Basic solution
• C. Acidic solution
• D. Alkaline solution

[1]

3. Which of the following is a product when phosphorus reacts with oxygen?

• A. Phosphorus pentoxide
• B. Phosphorus chloride
• C. Phosphorus hydride
• D. Phosphorus nitrate

[1]

4. What colour does universal indicator turn in a solution of a non-metal oxide dissolved in water?

• A. Blue or purple
• B. Green
• C. Red or orange
• D. Yellow only

[1]

Section B: True or False

1. Non-metal oxides are generally basic in nature. [1]

2. When sulfur burns in oxygen, it produces a substance with a choking smell. [1]

3. The reaction between carbon and oxygen is an endothermic reaction. [1]

4. Nitrogen gas reacts readily with oxygen at room temperature. [1]

Section C: Match the Column

Match the non-metal in Column A with its oxide in Column B. Write only the letter of the correct answer.

[4]

Section D: Fill in the Blanks

Word Bank: acidic, combustion, exothermic, non-metal oxides

1. When non-metals react with oxygen, the reaction is usually ________. [1]

2. The burning of a substance in oxygen is known as ________. [1]

3. Most ________ dissolve in water to form acidic solutions. [1]

4. Solutions of non-metal oxides in water are generally ________. [1]

Section E: Short Questions

1. Write a balanced chemical equation for the reaction of carbon with oxygen. [3]

2. Explain why non-metal oxides are called acidic oxides. [2]

3. Describe one safety precaution that should be taken when burning sulfur in the laboratory. [2]

4. State two observable signs that indicate a chemical reaction is occurring when a non-metal burns in oxygen. [2]

Section F: Scenario Question

Thandi conducted an experiment in her science class. She burned a small piece of charcoal in a gas jar filled with oxygen. After the charcoal stopped burning, she added a small amount of water to the gas jar, closed it with a stopper, and shook it well. She then tested the solution with blue litmus paper.

1. Name the gas produced when charcoal burns in oxygen. [1]

2. What change would Thandi observe when she adds blue litmus paper to the solution? [1]

3. Write the word equation for the reaction that occurs when charcoal burns in oxygen. [2]

4. Explain why the solution formed in the gas jar has the pH value that it does. [3]

Section G: Long Question

Bongani and Lerato were asked to investigate the products formed when different non-metals react with oxygen. They burned samples of carbon, sulfur, and phosphorus separately in oxygen and recorded their observations.

1. Write balanced chemical equations for the combustion of:

• (a) Carbon in excess oxygen [2]
• (b) Sulfur in oxygen [2]

2. Describe the procedure Bongani and Lerato should follow to test whether the oxide of sulfur forms an acidic solution when dissolved in water. [4]

3. Explain why all three non-metal oxides produced in this investigation are classified as acidic oxides. Include reference to what happens when these oxides dissolve in water. [4]

4. Evaluate the environmental impact of releasing large amounts of sulfur dioxide and nitrogen dioxide into the atmosphere. [3]

Grand Total: [50]

Answer Key

Well done on completing this worksheet! Before you check your answers, make sure you have attempted every question to the best of your ability. Use this answer key to mark your work carefully and learn from any mistakes. Remember, making mistakes is an important part of learning science!

Section A - Multiple Choice

Section A - Question 1
B. Carbon dioxide
When carbon burns in oxygen, it combines with oxygen to form carbon dioxide gas (CO₂). This is the same gas we breathe out and the gas that causes fizz in cold drinks.

Section A - Question 2
C. Acidic solution
Sulfur dioxide (SO₂) dissolves in water to form sulfurous acid, which makes the solution acidic. This is why non-metal oxides are often called acidic oxides.

Section A - Question 3
A. Phosphorus pentoxide
When phosphorus burns in oxygen, it forms phosphorus pentoxide (P₄O₁₀). The word "pentoxide" tells us there are five oxygen atoms bonded to the phosphorus.

Section A - Question 4
C. Red or orange
Universal indicator turns red or orange in acidic solutions. Since non-metal oxides dissolve in water to form acidic solutions, the indicator shows these acidic colours.

Section B - True or False

Section B - Question 1
FALSE
Corrected statement: Non-metal oxides are generally acidic in nature.
Non-metal oxides dissolve in water to form acids, not bases, so they are acidic rather than basic.

Section B - Question 2
TRUE
When sulfur burns in oxygen, it produces sulfur dioxide (SO₂), which has a sharp, choking smell that irritates the nose and throat.

Section B - Question 3
FALSE
Corrected statement: The reaction between carbon and oxygen is an exothermic reaction.
Combustion reactions release energy in the form of heat and light, which makes them exothermic, not endothermic.

Section B - Question 4
FALSE
Corrected statement: Nitrogen gas does not react readily with oxygen at room temperature.
Nitrogen is very unreactive at room temperature and requires high temperatures (like in a car engine or lightning) to react with oxygen.

Section C - Match the Column

Section C - Answers

• 1. D - Carbon reacts with oxygen to form carbon dioxide (CO₂).
• 2. A - Sulfur reacts with oxygen to form sulfur dioxide (SO₂).
• 3. B - Nitrogen reacts with oxygen under certain conditions to form nitrogen dioxide (NO₂).
• 4. C - Phosphorus reacts with oxygen to form phosphorus pentoxide (P₄O₁₀).

Section D - Fill in the Blanks

Section D - Question 1
exothermic
Reactions of non-metals with oxygen release energy as heat and light, making them exothermic.

Section D - Question 2
combustion
Combustion is the scientific term for burning, which is a reaction with oxygen that produces heat and light.

Section D - Question 3
non-metal oxides
Non-metal oxides are compounds formed when non-metals react with oxygen, and most of them dissolve in water to make acids.

Section D - Question 4
acidic
When non-metal oxides dissolve in water, they form acids, so the solutions are acidic in nature.

Section E - Short Questions

Section E - Question 1
Model Answer:
The balanced chemical equation is:
\[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \]
or in words: carbon + oxygen → carbon dioxide
• Correct reactants [1]
• Correct product [1]
• Balanced equation [1]

Section E - Question 2
Model Answer:
Non-metal oxides are called acidic oxides because when they dissolve in water, they form acidic solutions. For example, carbon dioxide forms carbonic acid and sulfur dioxide forms sulfurous acid.
• Reference to dissolving in water [1]
• Formation of acidic solutions [1]

Section E - Question 3
Model Answer:
One safety precaution is to work in a well-ventilated area or fume cupboard because sulfur dioxide gas produced is toxic and has a choking smell that can irritate the lungs.
• Correct safety precaution [1]
• Reason for precaution [1]

Section E - Question 4
Model Answer:
Two observable signs are: production of light (flame) and release of heat (the substance gets hot). You might also observe smoke or a colour change.
• First sign [1]
• Second sign [1]

Section F - Scenario Question

Section F - Question 1
Carbon dioxide (CO₂) is produced when charcoal (which is mainly carbon) burns in oxygen.

Section F - Question 2
The blue litmus paper would turn red (or pink), showing that the solution is acidic.

Section F - Question 3
Word equation:
carbon + oxygen → carbon dioxide
or
charcoal + oxygen → carbon dioxide
• Correct reactants [1]
• Correct product [1]

Section F - Question 4
Model Answer:
The solution has a low pH (acidic) because the carbon dioxide produced dissolves in the water to form carbonic acid (H₂CO₃). This acid releases hydrogen ions (H⁺) into the solution, which lowers the pH below 7.
• Identification that pH is low/acidic [1]
• Carbon dioxide dissolves to form carbonic acid [1]
• Reference to hydrogen ions or acid formation [1]

Section G - Long Question

Section G - Question 1(a)
\[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \]
• Correct formula equation [1]
• Balanced [1]

Section G - Question 1(b)
\[ \text{S} + \text{O}_2 \rightarrow \text{SO}_2 \]
• Correct formula equation [1]
• Balanced [1]

Section G - Question 2
Model Answer (Procedure):

1. Burn sulfur in oxygen inside a gas jar and allow it to cool. [1]
2. Add a small amount of distilled water to the gas jar and shake to dissolve the sulfur dioxide. [1]
3. Test the solution with universal indicator or blue litmus paper. [1]
4. If the indicator turns red/orange or blue litmus turns red, the solution is acidic. [1]

Section G - Question 3
Model Answer:
All three non-metal oxides are classified as acidic oxides because when they dissolve in water, they form acids. Carbon dioxide forms carbonic acid, sulfur dioxide forms sulfurous acid, and phosphorus pentoxide forms phosphoric acid. These acids release hydrogen ions (H⁺) in solution, which makes the pH less than 7.
• Statement that they dissolve in water [1]
• Formation of acids [1]
• Example of at least one acid formed [1]
• Reference to hydrogen ions or pH < 7="">

Section G - Question 4
Model Answer:
Sulfur dioxide and nitrogen dioxide are harmful to the environment because they dissolve in rainwater to form acid rain. Acid rain damages buildings, statues, and monuments, harms plants and crops, and makes rivers and lakes acidic, which kills fish and other aquatic life. These gases also contribute to respiratory problems in humans and animals.
• Formation of acid rain [1]
• Environmental damage (buildings, plants, water bodies) [1]
• Health impact [1]

Mark Allocation Summary