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Question (41)

QN0035912

Na2CO3 is converted into washing soda by crystallisation. Which formula represents washing soda in the chapter?

(A) NaHCO3
(B) Na2CO3·10H2O
(C) NaCl
(D) CaSO4·2H2O

Correct Answer: B

Explanation:

Washing soda is sodium carbonate decahydrate, Na2CO3·10H2O.

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Question (42)

QN0035913

A crystal of CuSO4·5H2O is heated strongly. Which change should be expected?

(A) It gains five water molecules and becomes darker blue
(B) Water of crystallisation is removed and the salt becomes white
(C) It changes directly into NaCl
(D) It produces chlorine gas

Correct Answer: B

Explanation:

Heating hydrated copper sulphate removes its water of crystallisation and the salt turns white.

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Question (43)

QN0035914

A sample of anhydrous copper sulphate is moistened with water. What observation supports the presence of water of crystallisation in the original crystals?

(A) Blue colour reappears
(B) The sample becomes black
(C) CO2 is released
(D) The sample becomes red

Correct Answer: A

Explanation:

Adding water restores the blue colour of copper sulphate crystals.

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Question (44)

QN0035915

One formula unit of CuSO4·5H2O contains how many water molecules as water of crystallisation?

(A) 2
(B) 4
(C) 5
(D) 10

Correct Answer: C

Explanation:

Five water molecules are present in one formula unit of hydrated copper sulphate.

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Question (45)

QN0035916

Gypsum has the formula CaSO4·2H2O. On heating at 373 K it loses water and forms:

(A) Sodium carbonate
(B) Calcium sulphate hemihydrate
(C) Calcium carbonate
(D) Sodium hydrogencarbonate

Correct Answer: B

Explanation:

Heating gypsum at 373 K forms calcium sulphate hemihydrate, called Plaster of Paris.

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Question (46)

QN0035917

Plaster of Paris is mixed with water and becomes a hard solid mass. Which substance is formed again?

(A) Gypsum
(B) Sodium chloride
(C) Bleaching powder
(D) Sodium carbonate

Correct Answer: A

Explanation:

Plaster of Paris reacts with water to change back into gypsum, producing a hard solid mass.

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Question (47)

QN0035918

Why should Plaster of Paris be stored in a moisture-proof container?

(A) It reacts with moisture and changes back into gypsum
(B) It absorbs oxygen and becomes chlorine
(C) It produces baking soda on contact with air
(D) It dissolves immediately into HCl

Correct Answer: A

Explanation:

Plaster of Paris reacts with water to form gypsum; therefore moisture can cause the material to set.

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Question (48)

QN0035919

A student compares two solutions: A has pH 6 and B has pH 8. Which statement correctly compares their nature?

(A) A is weakly acidic and B is weakly alkaline
(B) A is strongly alkaline and B is strongly acidic
(C) Both are neutral
(D) Both are acidic

Correct Answer: A

Explanation:

A pH below 7 indicates an acidic solution, while a pH above 7 indicates a basic solution.

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Question (49)

QN0035920

A solution has pH 11. It is gradually diluted with water. Which change is most consistent with dilution?

(A) Its OH- concentration per unit volume decreases and its pH moves toward the neutral range
(B) Its OH- concentration per unit volume increases indefinitely
(C) Its pH must become 1 immediately
(D) It becomes a strong acid immediately

Correct Answer: A

Explanation:

Dilution decreases ion concentration per unit volume; a basic solution becomes less concentrated as it is diluted.

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Question (50)

QN0035921

A student is given the following observations: (I) blue litmus turns red, (II) a metal produces hydrogen with the solution, (III) the solution conducts electricity in water, and (IV) the solution has pH 3. Which combination most strongly identifies an acidic solution?

(A) I and II only
(B) II and IV only
(C) I, II, III and IV
(D) III and IV only

Correct Answer: C

Explanation:

Acids show blue-litmus-to-red change, produce hydrogen with suitable metals, conduct electricity in aqueous solution due to ions, and have pH below 7.

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Question (41)

Na2CO3 is converted into washing soda by crystallisation. Which formula represents washing soda in the chapter?

Explanation:

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Question (42)

A crystal of CuSO4·5H2O is heated strongly. Which change should be expected?

Explanation:

Link:

Question (43)

A sample of anhydrous copper sulphate is moistened with water. What observation supports the presence of water of crystallisation in the original crystals?

Explanation:

Link:

Question (44)

One formula unit of CuSO4·5H2O contains how many water molecules as water of crystallisation?

Explanation:

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Question (45)

Gypsum has the formula CaSO4·2H2O. On heating at 373 K it loses water and forms:

Explanation:

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Question (46)

Plaster of Paris is mixed with water and becomes a hard solid mass. Which substance is formed again?

Explanation:

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Question (47)

Why should Plaster of Paris be stored in a moisture-proof container?

Explanation:

Link:

Question (48)

A student compares two solutions: A has pH 6 and B has pH 8. Which statement correctly compares their nature?

Explanation:

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Question (49)

A solution has pH 11. It is gradually diluted with water. Which change is most consistent with dilution?

Explanation:

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Question (50)

A student is given the following observations: (I) blue litmus turns red, (II) a metal produces hydrogen with the solution, (III) the solution conducts electricity in water, and (IV) the solution has pH 3. Which combination most strongly identifies an acidic solution?

Explanation:

Link:

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