Class 10 Science – Reaction of Metals with Salt Solutions

Class 10 Science – Chapter 2

Reaction of Metals with Salt Solutions

अम्ल, क्षार एवं लवण | Acids, Bases and Salts

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1. What is a Displacement Reaction?

English:
A displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound.

हिंदी:
विस्थापन अभिक्रिया वह रासायनिक अभिक्रिया है जिसमें अधिक क्रियाशील तत्व, कम क्रियाशील तत्व को उसके यौगिक से विस्थापित कर देता है।

General Form / सामान्य रूप

A + BC → AC + B

यदि A, B से अधिक क्रियाशील है, तो A, B को उसके यौगिक BC से विस्थापित कर देगा।

Example 1: Zinc and Copper Sulphate

Zn + CuSO₄ → ZnSO₄ + Cu

जिंक, कॉपर से अधिक क्रियाशील है। इसलिए Zn, CuSO₄ से Cu को विस्थापित कर देता है।

Example 2: Iron and Copper Sulphate

Fe + CuSO₄ → FeSO₄ + Cu

Iron is more reactive than copper, so iron displaces copper from copper sulphate solution.

Example 3: Copper and Zinc Sulphate

Cu + ZnSO₄ → No Reaction

Copper is less reactive than zinc. Therefore, copper cannot displace zinc from zinc sulphate.

Exam Point:
A more reactive metal can displace a less reactive metal from its salt solution.

अधिक क्रियाशील धातु, कम क्रियाशील धातु को उसके लवण विलयन से विस्थापित कर सकती है।

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2. Why Does Iron Displace Copper from Copper Sulphate?

English:
Iron displaces copper from copper sulphate because iron is more reactive than copper.

हिंदी:
लोहा कॉपर सल्फेट से कॉपर को इसलिए विस्थापित करता है क्योंकि लोहा, कॉपर से अधिक क्रियाशील है।

Reaction / अभिक्रिया

Fe + CuSO₄ → FeSO₄ + Cu

Observations / अवलोकन

• Blue colour of CuSO₄ solution gradually changes to green.
• CuSO₄ का नीला रंग धीरे-धीरे हरा हो जाता है।
• Reddish-brown copper is deposited.
• लाल-भूरे रंग का कॉपर जमा होता है।

Why does the colour change?

Copper sulphate solution is blue because of Cu²⁺ ions. During the reaction, Fe²⁺ ions are formed and FeSO₄ solution is pale green.

CuSO₄ विलयन का नीला रंग Cu²⁺ आयनों के कारण होता है। अभिक्रिया के बाद Fe²⁺ आयन बनते हैं और FeSO₄ का विलयन हल्का हरा होता है।

Electronic Explanation

Fe → Fe²⁺ + 2e⁻

Iron loses electrons and forms Fe²⁺ ions.

Cu²⁺ + 2e⁻ → Cu

Copper ions gain electrons and form metallic copper.

Conclusion:
Iron is oxidised while Cu²⁺ is reduced. Therefore, the reaction is also a redox reaction.

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3. Reaction Between Zinc and Copper Sulphate

English:
When zinc is placed in copper sulphate solution, zinc displaces copper from copper sulphate because zinc is more reactive than copper.

हिंदी:
जब जिंक को कॉपर सल्फेट के विलयन में डाला जाता है, तो जिंक कॉपर को विस्थापित कर देता है क्योंकि जिंक, कॉपर से अधिक क्रियाशील है।

Balanced Chemical Equation

Zn + CuSO₄ → ZnSO₄ + Cu

Observation / अवलोकन

• Blue CuSO₄ solution loses its blue colour.
• नीला CuSO₄ विलयन अपना नीला रंग खो देता है।
• Reddish-brown copper gets deposited on zinc.
• जिंक की सतह पर लाल-भूरा कॉपर जमा होता है।

Ionic Equation

Zn + Cu²⁺ → Zn²⁺ + Cu

Oxidation and Reduction

Zn → Zn²⁺ + 2e⁻

Zn is oxidised.

Cu²⁺ + 2e⁻ → Cu

Cu²⁺ is reduced.

Therefore:
Zn is the reducing agent and Cu²⁺ acts as the oxidising species. The reaction is displacement as well as redox reaction.

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4. Reactivity Series & Applications

Reactivity Series of Metals

K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au

The metals are arranged in decreasing order of their reactivity.

धातुओं को उनकी क्रियाशीलता के घटते क्रम में व्यवस्थित किया जाता है।

Important Rules

Rule 1: A more reactive metal displaces a less reactive metal from its salt solution.

Rule 2: A less reactive metal cannot displace a more reactive metal.

Examples

Zn + CuSO₄ → ZnSO₄ + Cu

Fe + CuSO₄ → FeSO₄ + Cu

Cu + FeSO₄ → No Reaction

Ag + CuSO₄ → No Reaction

Competitive Concept

Suppose metal A displaces metal B from BSO₄ solution. This means A is more reactive than B.

Shortcut:
Displacement possible → Reactivity of added metal > Reactivity of metal in salt.

Example

If X displaces Y from YSO₄, then:

X > Y

If Y cannot displace X from XSO₄:

X > Y

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30 MCQs – Reaction of Metals with Salt Solutions

1. What type of reaction occurs when Zn reacts with CuSO₄?

A. Combination

B. Displacement

C. Decomposition

D. Neutralisation

Answer: B. Displacement

Zn displaces Cu from CuSO₄.

2. Which metal can displace copper from CuSO₄?

A. Ag

B. Au

C. Zn

D. Pt

Answer: C. Zn

Zn is more reactive than Cu.

3. What is the colour of CuSO₄ solution?

A. Green

B. Blue

C. Yellow

D. Colourless

Answer: B. Blue

Cu²⁺ ions impart blue colour to the solution.

4. What is formed when Zn reacts with CuSO₄?

A. ZnCl₂

B. ZnSO₄ and Cu

C. CuCl₂

D. ZnO

Answer: B. ZnSO₄ and Cu

5. Which metal is more reactive?

A. Cu

B. Zn

C. Ag

D. Au

Answer: B. Zn

6. Fe + CuSO₄ gives:

A. FeSO₄ + Cu

B. FeCl₂ + Cu

C. CuO + Fe

D. No reaction

Answer: A. FeSO₄ + Cu

7. The colour of FeSO₄ solution is generally:

A. Blue

B. Pale green

C. Red

D. Black

Answer: B. Pale green

8. Copper cannot displace zinc from ZnSO₄ because:

A. Cu is more reactive

B. Zn is more reactive

C. Both are equally reactive

D. Cu is non-metal

Answer: B. Zn is more reactive

9. In Zn + CuSO₄ → ZnSO₄ + Cu, Zn is:

A. Reduced

B. Oxidised

C. Neutralised

D. Decomposed

Answer: B. Oxidised

10. In the same reaction, Cu²⁺ is:

A. Oxidised

B. Reduced

C. Neutralised

D. Decomposed

Answer: B. Reduced

11. Which equation is correctly balanced?

A. Zn + CuSO₄ → ZnSO₄ + Cu

B. Zn₂ + CuSO₄ → ZnSO₄ + Cu

C. Zn + 2CuSO₄ → ZnSO₄ + Cu

D. ZnSO₄ → Zn + Cu

Answer: A

12. A displacement reaction depends mainly on:

A. Colour

B. Reactivity

C. Density only

D. Melting point

Answer: B. Reactivity

13. Which is more reactive?

A. Fe

B. Cu

C. Ag

D. Au

Answer: A. Fe

14. What deposits on zinc in CuSO₄ solution?

A. Iron

B. Copper

C. Silver

D. Sulphur

Answer: B. Copper

15. Cu + ZnSO₄ results in:

A. Zn + CuSO₄

B. No reaction

C. CuSO₄ + H₂

D. ZnO

Answer: B. No reaction

16. The ionic equation for zinc and copper sulphate is:

A. Zn + Cu²⁺ → Zn²⁺ + Cu

B. Zn²⁺ + Cu → Zn + Cu²⁺

C. Zn + SO₄²⁻ → ZnSO₄

D. Cu + SO₄²⁻ → CuSO₄

Answer: A

17. Which species gains electrons?

A. Zn

B. Cu²⁺

C. SO₄²⁻

D. Zn²⁺

Answer: B. Cu²⁺

18. Which species loses electrons?

A. Cu²⁺

B. Zn

C. Cu

D. SO₄²⁻

Answer: B. Zn

19. Oxidation of Zn is represented by:

A. Zn → Zn²⁺ + 2e⁻

B. Zn²⁺ + 2e⁻ → Zn

C. Cu²⁺ → Cu

D. Cu → Cu²⁺

Answer: A

20. Reduction of copper ion is:

A. Cu → Cu²⁺ + 2e⁻

B. Cu²⁺ + 2e⁻ → Cu

C. Zn → Zn²⁺

D. SO₄²⁻ → SO₂

Answer: B

21. Which metal is below copper in the reactivity series?

A. Zn

B. Fe

C. Ag

D. Mg

Answer: C. Ag

22. Which metal can displace Fe from FeSO₄?

A. Cu

B. Ag

C. Zn

D. Au

Answer: C. Zn

23. Which reaction is impossible?

A. Zn + CuSO₄

B. Fe + CuSO₄

C. Cu + ZnSO₄

D. Mg + CuSO₄

Answer: C. Cu + ZnSO₄

24. A displacement reaction is also often:

A. Redox reaction

B. Neutralisation

C. Photochemical reaction only

D. Polymerisation

Answer: A. Redox reaction

25. In Fe + CuSO₄, the blue colour changes because:

A. FeSO₄ is formed

B. CuSO₄ becomes CuO

C. Water evaporates

D. Copper dissolves completely

Answer: A. FeSO₄ is formed

26. Which metal is the least reactive among these?

A. Zn

B. Fe

C. Cu

D. Ag

Answer: D. Ag

27. If A displaces B from BSO₄, then:

A. A is less reactive than B

B. A is more reactive than B

C. A and B are non-metals

D. A and B have equal reactivity

Answer: B

28. Which product contains the displaced metal?

A. ZnSO₄ in Zn + CuSO₄

B. Cu in Zn + CuSO₄

C. SO₄ only

D. Zn only

Answer: B. Cu

29. The reactivity of Zn compared with Cu is:

A. Zn < Cu

B. Zn > Cu

C. Zn = Cu

D. Cannot be compared

Answer: B. Zn > Cu

30. The best definition of displacement reaction is:

A. Two compounds exchange ions

B. One element replaces another element from its compound

C. One compound breaks down

D. Acid reacts with base

Answer: B

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30 Subjective Questions – Complete Solutions

1 Mark Questions

Q1. What is a displacement reaction?

एक अधिक क्रियाशील तत्व द्वारा कम क्रियाशील तत्व को उसके यौगिक से विस्थापित करने की अभिक्रिया विस्थापन अभिक्रिया कहलाती है।

Q2. Which metal can displace copper from CuSO₄?

Zinc (Zn), Iron (Fe), Magnesium (Mg) आदि।

Q3. Write the reaction between zinc and copper sulphate.

Zn + CuSO₄ → ZnSO₄ + Cu

Q4. Which is more reactive: Zn or Cu?

Zinc is more reactive than copper.

Q5. What is deposited when Zn is placed in CuSO₄ solution?

Reddish-brown copper is deposited.

2 Mark Questions

Q6. Why can zinc displace copper from CuSO₄?

Zinc is above copper in the reactivity series. Therefore, Zn is more reactive and displaces Cu from CuSO₄.

Q7. Why can copper not displace zinc from ZnSO₄?

Copper is less reactive than zinc. Hence, it cannot displace zinc from ZnSO₄.

Q8. Write two observations when Zn is added to CuSO₄ solution.

1. Blue colour of CuSO₄ decreases/disappears.
2. Reddish-brown copper is deposited on zinc.

Q9. Why does Fe displace Cu from CuSO₄?

Fe is more reactive than Cu and lies above Cu in the reactivity series. Hence Fe displaces Cu.

Q10. State the general form of a displacement reaction.

A + BC → AC + B
provided A is more reactive than B.

3 Mark Questions

Q11. Explain the reaction between Fe and CuSO₄.

Iron is more reactive than copper. Therefore, Fe displaces Cu from CuSO₄.

Fe + CuSO₄ → FeSO₄ + Cu

The blue CuSO₄ solution changes towards pale green due to formation of FeSO₄, and copper is deposited.

Q12. Explain Zn + CuSO₄ using electron transfer.

Oxidation:
Zn → Zn²⁺ + 2e⁻

Reduction:
Cu²⁺ + 2e⁻ → Cu

Therefore, Zn is oxidised and Cu²⁺ is reduced.

Q13. Why is displacement reaction also a redox reaction?

In a displacement reaction, one metal loses electrons while the displaced metal ion gains electrons. Thus oxidation and reduction occur simultaneously, making it a redox reaction.

Q14. Give three examples of displacement reactions.

Zn + CuSO₄ → ZnSO₄ + Cu
Fe + CuSO₄ → FeSO₄ + Cu
Mg + CuSO₄ → MgSO₄ + Cu

Q15. Explain the importance of reactivity series in displacement reactions.

The reactivity series helps us predict whether a displacement reaction will occur. A metal higher in the series can displace a metal lower in the series from its salt solution.

4 Mark Questions

Q16. Describe an experiment to show displacement of copper by zinc.

Take a blue CuSO₄ solution in a beaker and immerse a clean zinc strip in it. After some time, the blue colour fades and reddish-brown copper gets deposited on zinc.

Equation:
Zn + CuSO₄ → ZnSO₄ + Cu

This proves that Zn is more reactive than Cu.

Q17. Compare Zn + CuSO₄ and Cu + ZnSO₄.

Zn + CuSO₄ → ZnSO₄ + Cu — reaction occurs because Zn is more reactive than Cu.

Cu + ZnSO₄ → No reaction — Cu is less reactive than Zn.

Q18. Explain the colour change in Fe + CuSO₄ reaction.

CuSO₄ solution is blue due to Cu²⁺ ions. Fe displaces Cu and forms FeSO₄. FeSO₄ solution is pale green.

Fe + CuSO₄ → FeSO₄ + Cu

Q19. Explain oxidation and reduction in Zn + CuSO₄.

Zn loses two electrons:
Zn → Zn²⁺ + 2e⁻

Cu²⁺ gains two electrons:
Cu²⁺ + 2e⁻ → Cu

Thus Zn undergoes oxidation and Cu²⁺ undergoes reduction.

Q20. Predict whether the following reactions occur:
(i) Cu + ZnSO₄
(ii) Zn + FeSO₄
(iii) Fe + CuSO₄

(i) No reaction — Cu is less reactive than Zn.
(ii) Reaction occurs — Zn is more reactive than Fe.
(iii) Reaction occurs — Fe is more reactive than Cu.

5 Mark Questions

Q21. Explain displacement reaction with suitable examples.

A displacement reaction occurs when a more reactive element replaces a less reactive element from its compound.

General:
A + BC → AC + B

Examples:
Zn + CuSO₄ → ZnSO₄ + Cu
Fe + CuSO₄ → FeSO₄ + Cu
Mg + CuSO₄ → MgSO₄ + Cu

These reactions are possible because the added metals are more reactive than copper.

Q22. Explain the complete reaction between zinc and copper sulphate.

Zinc is placed in blue CuSO₄ solution. Zinc is more reactive than copper and displaces it.

Molecular equation:
Zn + CuSO₄ → ZnSO₄ + Cu

Ionic equation:
Zn + Cu²⁺ → Zn²⁺ + Cu

Oxidation:
Zn → Zn²⁺ + 2e⁻

Reduction:
Cu²⁺ + 2e⁻ → Cu

Copper appears as a reddish-brown deposit.

Q23. Explain how reactivity series predicts displacement reactions.

The reactivity series arranges metals from most reactive to least reactive.

K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au

A metal higher in the series displaces a metal lower in the series from its salt solution.

For example:
Zn > Cu
Therefore:
Zn + CuSO₄ → ZnSO₄ + Cu

But:
Cu + ZnSO₄ → No reaction.

Q24. Explain Fe + CuSO₄ reaction with observations and reason.

Iron is more reactive than copper. Therefore iron displaces copper from copper sulphate.

Equation:
Fe + CuSO₄ → FeSO₄ + Cu

Observations:
1. Blue colour of CuSO₄ changes towards pale green.
2. Reddish-brown copper is deposited.
3. Iron slowly dissolves.

Reason: Fe lies above Cu in the reactivity series.

Q25. Differentiate between displacement and double displacement reactions.

Displacement: One element displaces another element from a compound.
Example:
Zn + CuSO₄ → ZnSO₄ + Cu

Double displacement: Two compounds exchange their ions.
Example:
AgNO₃ + NaCl → AgCl + NaNO₃

6 Mark Questions

Q26. Give a detailed explanation of Zn + CuSO₄ reaction including ionic and redox equations.

Zinc is more reactive than copper, so it displaces copper from copper sulphate.

Molecular equation:
Zn + CuSO₄ → ZnSO₄ + Cu

Ionic equation:
Zn + Cu²⁺ → Zn²⁺ + Cu

Oxidation:
Zn → Zn²⁺ + 2e⁻

Reduction:
Cu²⁺ + 2e⁻ → Cu

Zinc loses electrons and is oxidised. Copper ions gain electrons and are reduced. Therefore, the reaction is both displacement and redox.

Q27. Explain experimentally how you can prove that Zn is more reactive than Cu.

Take CuSO₄ solution in a test tube and immerse a clean zinc strip.

The blue colour gradually fades and reddish-brown copper deposits on zinc.

Equation:
Zn + CuSO₄ → ZnSO₄ + Cu

This shows that Zn has displaced Cu. Hence Zn is more reactive than Cu.

Q28. A student performs the following reactions. Predict the products and explain:
(a) Zn + CuSO₄
(b) Cu + ZnSO₄
(c) Fe + CuSO₄

(a) Zn + CuSO₄ → ZnSO₄ + Cu
Reason: Zn is more reactive than Cu.

(b) Cu + ZnSO₄ → No reaction
Reason: Cu is less reactive than Zn.

(c) Fe + CuSO₄ → FeSO₄ + Cu
Reason: Fe is more reactive than Cu.

Q29. Explain the relationship between displacement reaction and reactivity series.

The reactivity series determines whether one metal can displace another from its salt solution.

If metal A is above metal B:
A > B

then:
A + B-salt → A-salt + B

Example:
Zn > Cu
Therefore:
Zn + CuSO₄ → ZnSO₄ + Cu

If A is below B, displacement does not occur.

Q30. Explain why displacement reactions are important in chemistry.

Displacement reactions are important because:

1. They demonstrate relative reactivity of metals.
2. They help establish the reactivity series.
3. They explain extraction and recovery of some metals.
4. They demonstrate oxidation-reduction processes.
5. They help predict whether a reaction will occur.
6. They provide experimental evidence for electron transfer.

Example:
Zn + CuSO₄ → ZnSO₄ + Cu

This single reaction demonstrates displacement, oxidation, reduction and relative reactivity.

Class 10 Science | Acids, Bases and Salts
Reaction of Metals with Salt Solutions
Concept + Reactions + MCQs + Subjective Questions