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Question (21)

QN0035844

Iron nails are placed in copper sulphate solution. Which observation is expected after some time?

(A) The blue colour becomes more intense and no deposit forms
(B) A copper deposit forms and the blue colour fades
(C) The solution becomes colourless immediately
(D) Hydrogen gas is evolved

Correct Answer: B

Explanation:

Fe + CuSO₄ → FeSO₄ + Cu. Iron displaces copper from copper sulphate, causing copper to deposit and the blue colour to fade.

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Question (22)

QN0035845

In Fe + CuSO₄ → FeSO₄ + Cu, which element is displaced from its compound?

(A) Iron
(B) Sulphur
(C) Copper
(D) Oxygen

Correct Answer: C

Explanation:

Iron replaces or displaces copper from copper sulphate.

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Question (23)

QN0035846

If 3 Fe atoms react according to Fe + CuSO₄ → FeSO₄ + Cu, how many Cu atoms can theoretically be displaced, assuming sufficient CuSO₄?

(A) 1
(B) 2
(C) 3
(D) 6

Correct Answer: C

Explanation:

The reaction has a 1:1 ratio between Fe and Cu displaced. Therefore, 3 Fe atoms can displace 3 Cu atoms.

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Question (24)

QN0035847

Which of the following is a displacement reaction?

(A) Zn + CuSO₄ → ZnSO₄ + Cu
(B) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
(C) CaCO₃ → CaO + CO₂
(D) CaO + H₂O → Ca(OH)₂

Correct Answer: A

Explanation:

Zinc displaces copper from copper sulphate, forming zinc sulphate and copper.

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Question (25)

QN0035848

In the reaction Pb + CuCl₂ → PbCl₂ + Cu, if 2 Pb atoms react completely, the number of Cu atoms produced is

(A) 1
(B) 2
(C) 3
(D) 4

Correct Answer: B

Explanation:

The reaction ratio of Pb to Cu is 1:1. Therefore, 2 Pb atoms produce 2 Cu atoms.

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Question (26)

QN0035849

Sodium sulphate solution is mixed with barium chloride solution. A white insoluble substance forms. Which substance is the precipitate?

(A) NaCl
(B) BaCl₂
(C) Na₂SO₄
(D) BaSO₄

Correct Answer: D

Explanation:

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl. BaSO₄ is insoluble in water and forms the white precipitate.

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Question (27)

QN0035850

In Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl, the number of NaCl units formed per one BaSO₄ unit is

(A) 1
(B) 2
(C) 3
(D) 4

Correct Answer: B

Explanation:

The balanced equation contains a coefficient of 2 before NaCl, so two NaCl units are formed per BaSO₄ unit.

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Question (28)

QN0035851

A reaction involves exchange of ions between two compounds and produces an insoluble salt. It is best described as

(A) combination only
(B) decomposition only
(C) double displacement and precipitation
(D) displacement only

Correct Answer: C

Explanation:

Exchange of ions makes it a double displacement reaction, while formation of an insoluble salt makes it a precipitation reaction.

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Question (29)

QN0035852

Which pair correctly represents the products of Na₂SO₄ reacting with BaCl₂?

(A) NaCl and BaSO₄
(B) Na₂Cl and BaSO₄
(C) NaSO₄ and BaCl
(D) Na and BaCl₂

Correct Answer: A

Explanation:

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl.

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Question (30)

QN0035853

Copper powder is heated in air and becomes coated with a black substance. The black substance is

(A) Cu₂O
(B) CuO
(C) CuSO₄
(D) CuCO₃

Correct Answer: B

Explanation:

Copper gains oxygen on heating: 2Cu + O₂ → 2CuO. Copper oxide is black.

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Question (21)

Iron nails are placed in copper sulphate solution. Which observation is expected after some time?

Explanation:

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Question (22)

In Fe + CuSO₄ → FeSO₄ + Cu, which element is displaced from its compound?

Explanation:

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Question (23)

If 3 Fe atoms react according to Fe + CuSO₄ → FeSO₄ + Cu, how many Cu atoms can theoretically be displaced, assuming sufficient CuSO₄?

Explanation:

Link:

Question (24)

Which of the following is a displacement reaction?

Explanation:

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Question (25)

In the reaction Pb + CuCl₂ → PbCl₂ + Cu, if 2 Pb atoms react completely, the number of Cu atoms produced is

Explanation:

Link:

Question (26)

Sodium sulphate solution is mixed with barium chloride solution. A white insoluble substance forms. Which substance is the precipitate?

Explanation:

Link:

Question (27)

In Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl, the number of NaCl units formed per one BaSO₄ unit is

Explanation:

Link:

Question (28)

A reaction involves exchange of ions between two compounds and produces an insoluble salt. It is best described as

Explanation:

Link:

Question (29)

Which pair correctly represents the products of Na₂SO₄ reacting with BaCl₂?

Explanation:

Link:

Question (30)

Copper powder is heated in air and becomes coated with a black substance. The black substance is

Explanation:

Link:

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