Answer the following. (a) What is the effect of temperature on the solubility of glucose in water? (b) Ibrahim collected a 10mL each of fresh water and ocean water. He observed that one sample labeled "P" froze at 0 °C while the other "Q" at -1.3°C. Ibrahim forgot which of the two, "P" or "Q" was ocean water. Help him identify which container contains ocean water, giving rationalization for your answer. (c) Calculate Van't Hoff factor for an aqueous solution of K_3[Fe(CN)_6] if the degree of dissociation (α) is 0.852. What will be boiling point of this solution if its concentration is 1 molal? (K_b=0.52 K kg/mol)

ChemistryCBSE Class 12 · Sample paper, session 2023-24 · 5 marks · Long answer

CBSE Class 12 Chemistry sample paper 2023-24: question 32(a)

From the official CBSE sample question paper for 2023-24, section E, question 32(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(a) · 5 marks · Long answerSolutions

Answer the following.

(a)
What is the effect of temperature on the solubility of glucose in water?
0 marks
(b)
Ibrahim collected a 10mL each of fresh water and ocean water. He observed that one sample labeled "P" froze at 0 °C while the other "Q" at -1.3°C. Ibrahim forgot which of the two, "P" or "Q" was ocean water. Help him identify which container contains ocean water, giving rationalization for your answer.
0 marks
(c)
Calculate Van't Hoff factor for an aqueous solution of $K_{3} [Fe (CN)_{6}]$ if the degree of dissociation ( $α$ ) is 0.852. What will be boiling point of this solution if its concentration is 1 molal? ( $K_{b}$ =0.52 K kg/mol)
0 marks

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

Open one hint at a time and try again before the next.

Hint 1

Decide whether dissolving glucose absorbs or releases heat.

Hint 2

Dissolved salts change the freezing point of water — in which direction?

Hint 3

Count the ions from K₃[Fe(CN)₆], then use i = 1 + (n – 1)α and ΔTb = iKb m.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

(a) Dissolving glucose in water is endothermic. By Le Chatelier's principle, raising the temperature favours the endothermic dissolution, so the solubility of glucose increases.
1 mark
(b) Q (freezing at –1.3 °C) is ocean water. Its dissolved salts depress the freezing point below 0 °C ( $Δ T_{f} = i K_{f} m$ ), while fresh water P freezes at 0 °C.
1 mark
(c) $K_{3} [Fe (CN)_{6}] \to 3 K^{+} + [Fe (CN)_{6}]^{3 -}$ , so $n = 4$ ions.
½ mark
$i = 1 + (n - 1) α = 1 + (4 - 1) (0.852) = 3.556$
1 mark
$Δ T_{b} = i K_{b} m = 3.556 \times 0.52 \times 1 = 1.85 K$
1 mark
$T_{b} = 100 + 1.85 = 101.85^{\circ} C$ (≈ 375.0 K)
½ mark

Answer: (a) Solubility increases with temperature; (b) Q is ocean water; (c) i = 3.556, boiling point = 101.85 °C

Where the marks are

(a) Endothermic dissolution, so solubility rises with temperature (Le Chatelier) (1 mark)
(b) Q is ocean water, explained by depression of freezing point due to salts (1 mark)
(c) n = 4 ions (½ mark)
(c) i = 1 + (n–1)α = 3.556 (1 mark)
(c) ΔTb = 1.85 K (1 mark)
(c) Tb = 101.85 °C (½ mark)

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CBSE Class 12 Chemistry sample paper 2023-24: question 32(a)

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