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1. ⇒  (MHT CET 2023 12th May Morning Shift )

Which among the following solutions has minimum boiling point elevation?

A. 0.1   m   NaCl

B. 0.2   m   KNO 3

C. 0.1   m   Na 2 SO 4

D. 0.05   m   CaCl 2

Correct Option is (D)

NaCl Na + + Cl

Total ions = 0.1 + 0.1 = 0.2 ions

KNO 3 K + + NO 3

Total ions = 0.2 + 0.2 = 0.4 ions

Na 2 SO 4 2 Na + + SO 4 2

Total ions = 0.2 + 0.1 = 0.3 ions

CaCl 2 Ca 2 + + 2 Cl

Total ions = 0.05 + 0.1 = 0.15 ions

0.05   m CaCl 2 solution has minimum ions in solution, so it shows minimum boiling point elevation.

2. ⇒  (MHT CET 2023 11th May Morning Shift )

If K b denote molal elevation constant of water, then boiling point of an aqueous solution containing 36   g glucose (molar mass = 180 ) per dm 3 is:

A. ( 100 + K b ) C

B. ( 100 + 2   K b ) C

C. ( 100 + K b 10 ) C

D. ( 100 + 2   K b 10 ) C

Correct Option is (D)

The aqueous solution contains 36   g glucose per dm 3 , so mass of solute W 2 is 36   g .

Assuming that the density of solution is 1   g / dm 3 , the mass of solvent (water) is 1000   g .

Δ T b = 1000   K b W 2 M 2   W 1 Δ T b = 1000   g   kg 1 × K b × 36   g 180   g × 1000   g Δ T b = 2   K b 10 Δ T b = T b T b T b = T b + Δ T b T b = ( 100 + 2   K b 10 ) C

3. ⇒  (MHT CET 2023 11th May Morning Shift )

What is vapour pressure of a solution containing 1   mol of a nonvolatile solute in 36   g of water ( P 1 0 = 32   mm   Hg ) ?

A. 8.14   mm   Hg

B. 12.31   mm   Hg

C. 16.08   mm   Hg

D. 21.44   mm   Hg

Correct Option is (D)

n 2 = 1   mol n 1 = 36 18 = 2   mol

Relative lowering of vapour pressure

= P 1 0 P 1 P 1 0 = x 2 = n 2 n 1 + n 2

32   mm Hg P 1 32   mm Hg = 1 3 96   mm   Hg 3 P 1 = 32   mm   Hg 64   mm   Hg = 3 P 1 P 1 = 21.33   mm   Hg 21.44   mm   Hg

4. ⇒  (MHT CET 2023 9th May Morning Shift )

A solution of nonvolatile solute is obtained by dissolving 3.5   g in 100   g solvent has boiling point elevation 0.35   K . Calculate the molar mass of solute.

(Molal elevation constant = 2.5   K   kg   mol 1 )

A. 270   g   mol 1

B. 260   g   mol 1

C. 250   g   mol 1

D. 240   g   mol 1

Correct Option is (C)

M 2 = K b × W 2 × 1000 Δ T b × W 1 = 2.5 × 3.5 × 1000 0.35 × 100 = 250   g   mol 1

5. ⇒  (MHT CET 2021 21th September Evening Shift )

What is the boiling point of 0.5 molal aqueous solution of sucrose if 0.1 molal aqueous solution of glucose boils at 100.16 C?

A. 100.32 C

B. 100.80 C

C. 100.16 C

D. 100.62 C

Correct Option is (B)

For glucose solution, m = 0.1   m ,   T b = 100.16 C

Δ T b = T b T b = 100.16 100 = 0.16 C

K b = Δ T b m = 0.16 C 0.1   m = 1.6 C / m

For sucrose solution, m = 0.5   m ,   K b = 1.6 C / m

Δ T b = K b × m = 1.6 C / m × 0.5   m = 0.80 C Δ T b = T b T b T b = Δ T b + T b = 0.80 + 100 = 100.80 C