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Practise Class 10 Science Chapter 3 – Metals and Non-metals with 5 original NCERT-based MCQs on reactions of metals with oxygen, reduction of metal oxides, displacement reactions, corrosion and prevention of rusting, with detailed explanations.
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Chapter Information
Subject: Science
Class: 10
Chapter: Metals and Non-metals
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 3
Difficulty Level: Moderate
Based On: NCERT Syllabus
Content Type: Original Practice Questions
Introduction
Metals undergo different chemical reactions depending on their reactivity and the substances with which they interact. Their reactions with oxygen can produce metal oxides, while certain metals can displace less reactive metals from their salt solutions.
Metals may also deteriorate when exposed to air and moisture. This process is known as corrosion. Understanding corrosion and its prevention is important because it helps explain how metallic objects can be protected from damage.
This Practice Set 3 covers metal oxides, reduction, displacement reactions, corrosion and methods of preventing rusting.
What You Will Learn
- Reactions of metals with oxygen
- Reduction of metal oxides
- Displacement reactions
- Corrosion of metals
- Rusting of iron
- Methods of preventing corrosion
- Important chemical equations and concepts
Why This Topic Is Important
Chemical reactions and corrosion are important topics in Class 10 Science. Questions may test students’ ability to identify reaction products, understand how metals react and explain why iron rusts.
Learning the conditions required for rusting and the methods used to prevent corrosion also helps students connect chemistry with everyday life.
5 MCQs with Answers and Detailed Solutions
Q1. Which conditions are necessary for the rusting of iron under ordinary circumstances?
A) Oxygen only
B) Water only
C) Both oxygen and water
D) Nitrogen and carbon dioxide only
Answer: Both oxygen and water
Detailed Solution
Rusting is a form of corrosion in which iron reacts with oxygen in the presence of moisture. The process produces hydrated iron(III) oxide, commonly called rust.
Both oxygen and water are necessary for ordinary rusting. If either is excluded effectively, rusting can be prevented or greatly reduced.
This is why iron objects are often protected with paint, oil or other suitable coatings.
Therefore, Option C is correct.
Exam Tip
Remember that rusting requires both oxygen and moisture. Salt in water can accelerate corrosion, but salt is not essential for rusting.
Q2. Which substance is commonly used to protect iron from rusting by coating it with a layer of zinc?
A) Copper
B) Zinc
C) Silver
D) Gold
Answer: Zinc
Detailed Solution
The process of coating iron or steel with zinc is called galvanisation.
The zinc coating acts as a barrier that limits the contact of iron with oxygen and moisture. Zinc can also provide sacrificial protection because it is more reactive than iron.
Galvanisation is widely used to protect iron and steel objects such as certain pipes, sheets and outdoor structures.
Therefore, zinc is the correct answer.
Exam Tip
Do not confuse galvanisation with electroplating using other metals. Galvanisation specifically refers to applying a protective zinc coating to iron or steel.
Q3. What happens when copper(II) oxide is heated with hydrogen gas under suitable conditions?
A) Copper oxide changes into copper, and water is formed.
B) Copper oxide changes into copper sulphate.
C) Copper oxide produces copper chloride and oxygen.
D) No chemical reaction takes place.
Answer: Copper oxide changes into copper, and water is formed.
Detailed Solution
Hydrogen reacts with copper(II) oxide on heating. Hydrogen removes oxygen from copper(II) oxide, producing copper and water.
The balanced chemical equation is:
$$CuO + H_2 \rightarrow Cu + H_2O$$
In this reaction:
- Copper(II) oxide loses oxygen and is reduced to copper.
- Hydrogen gains oxygen and is oxidised to water.
This reaction illustrates the relationship between oxidation and reduction.
Therefore, Option A is correct.
Exam Tip
Reduction can involve the removal of oxygen from a substance, while oxidation can involve the addition of oxygen.
Q4. An iron strip is placed in copper sulphate solution. Which observation supports the occurrence of a displacement reaction?
A) The iron strip remains unchanged, and no reaction occurs.
B) Copper deposits on the iron strip, and the solution changes towards pale green.
C) The solution immediately becomes colourless because copper forms a gas.
D) The iron strip changes into silver.
Answer: Copper deposits on the iron strip, and the solution changes towards pale green.
Detailed Solution
Iron is more reactive than copper. Therefore, iron displaces copper from copper sulphate solution and forms iron(II) sulphate.
The balanced chemical equation is:
$$Fe + CuSO_4 \rightarrow FeSO_4 + Cu$$
Copper forms a reddish-brown deposit on the iron strip. The blue copper sulphate solution changes towards pale green as iron(II) sulphate forms.
These observations provide evidence of a displacement reaction.
Therefore, Option B is correct.
Exam Tip
Learn both the chemical equation and the expected observations. Examination questions may ask about either one.
Q5. Which method protects iron from corrosion by covering its surface with a protective layer of paint?
A) Painting
B) Melting
C) Crushing
D) Dissolving in water
Answer: Painting
Detailed Solution
Painting forms a protective coating over an iron surface. When the coating remains intact, it limits direct contact between iron and environmental oxygen and moisture.
This reduces the likelihood of rusting. For effective protection, the surface should be properly prepared, and damaged paint should be repaired.
Other methods of corrosion prevention include oiling, greasing, galvanisation and suitable electroplating.
Therefore, painting is the correct answer.
Exam Tip
Remember that protective coatings work by separating the metal surface from substances that cause corrosion. Some methods, such as galvanisation, can also provide additional protection if the coating is scratched.
Important Concepts
Corrosion
Corrosion is the gradual deterioration of a metal due to chemical or electrochemical reactions with its surroundings.
Examples include rusting of iron and the formation of a green coating on copper under suitable environmental conditions.
Rusting of Iron
Rusting occurs when iron is exposed to oxygen and moisture. Rust is commonly described as hydrated iron(III) oxide.
Rusting can weaken iron objects and damage structures over time.
Prevention of Rusting
Common methods include:
- Painting
- Oiling or greasing
- Galvanisation
- Suitable electroplating
- Using appropriate corrosion-resistant materials
The method chosen depends on the application and environmental conditions.
Oxidation and Reduction
Oxidation can involve the addition of oxygen, while reduction can involve the removal of oxygen.
In the reaction:
$$CuO + H_2 \rightarrow Cu + H_2O$$
Copper(II) oxide is reduced to copper, while hydrogen is oxidised to water.
Displacement Reactions
A more reactive metal can displace a less reactive metal from its salt solution.
For example:
$$Fe + CuSO_4 \rightarrow FeSO_4 + Cu$$
Iron displaces copper because iron is more reactive than copper.
Related Practice Questions
Q1. Why does iron rust more readily in moist air than in dry air?
Q2. What is galvanisation, and how does it help protect iron?
Q3. Write the balanced chemical equation for the reaction between copper(II) oxide and hydrogen.
Q4. What is the difference between oxidation and reduction in terms of oxygen transfer?
Q5. Why is painting an effective method of protecting iron from rusting?
Mini Quiz Challenge
Try answering these questions without looking at the answers.
Q1. Which two substances are required for ordinary rusting of iron?
A) Oxygen and water
B) Nitrogen and hydrogen
C) Carbon dioxide and nitrogen
D) Helium and oxygen
Q2. What is galvanisation?
A) Coating iron or steel with zinc
B) Coating iron with water
C) Heating iron until it melts
D) Mixing iron with sand
Q3. In the reaction below, which substance is reduced?
$$CuO + H_2 \rightarrow Cu + H_2O$$
A) Hydrogen
B) Copper(II) oxide
C) Water
D) Oxygen gas
Q4. Which metal displaces copper from copper sulphate solution?
A) Silver
B) Gold
C) Iron
D) Platinum
Q5. Which method reduces rusting by forming a protective barrier on iron?
A) Painting
B) Scratching
C) Crushing
D) Washing with salt water
Exam Tips
- Remember the conditions required for rusting.
- Learn the meaning of corrosion and distinguish it from rusting.
- Understand the purpose of galvanisation.
- Practise identifying oxidation and reduction in chemical equations.
- Learn the observations of the iron and copper sulphate displacement reaction.
- Remember that protective coatings must remain effective to provide barrier protection.
- Check chemical equations for correct formulas and balanced atoms.
Quick Revision Notes
- Corrosion is the gradual deterioration of a metal due to its surroundings.
- Rusting is the corrosion of iron in the presence of oxygen and moisture.
- Galvanisation involves coating iron or steel with zinc.
- Painting and oiling can protect metal surfaces by limiting contact with oxygen and moisture.
- Reduction can involve the removal of oxygen from a compound.
- Oxidation can involve the addition of oxygen to a substance.
- Iron displaces copper from copper sulphate solution.
- Copper(II) oxide reacts with hydrogen on heating to form copper and water.
Common Mistakes Students Make
- Assuming that water alone is sufficient for ordinary rusting of iron.
- Confusing corrosion with rusting; rusting specifically concerns iron.
- Forgetting that galvanisation uses zinc.
- Reversing the products and reactants in a chemical equation.
- Confusing oxidation with reduction.
- Assuming that all metals corrode in exactly the same way.
- Forgetting the colour changes associated with the iron and copper sulphate reaction.
Key Takeaways
- Rusting of iron requires oxygen and moisture under ordinary conditions.
- Corrosion can damage metallic objects and structures.
- Protective coatings help reduce contact between metals and corrosive surroundings.
- Galvanisation protects iron and steel by applying a zinc coating.
- Oxidation and reduction can be understood through the transfer of oxygen.
- Displacement reactions depend on the relative reactivity of metals.
FAQs
Q. What is rusting?
Answer:
Rusting is the corrosion of iron in the presence of oxygen and moisture. It produces hydrated iron(III) oxide, commonly called rust.
Q. What is galvanisation?
Answer:
Galvanisation is the process of coating iron or steel with zinc to protect it from corrosion.
Q. Why is painting used to protect iron?
Answer:
Paint forms a protective barrier that limits contact between iron and oxygen and moisture.
Q. What happens when hydrogen reacts with copper(II) oxide on heating?
Answer:
Hydrogen reduces copper(II) oxide to copper and is oxidised to water.
$$CuO + H_2 \rightarrow Cu + H_2O$$
Q. Why does iron displace copper from copper sulphate solution?
Answer:
Iron is more reactive than copper, so it displaces copper from copper sulphate solution.
Conclusion
Class 10 Science Chapter 3 – Metals and Non-metals covers corrosion, rusting, galvanisation, oxidation, reduction and displacement reactions. These original practice questions help students revise key concepts and understand chemical changes involving metals.
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