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MHT CET · Chemistry · Solutions

Calculate the depression in freezing point of solution when \(4 \mathrm{~g}\) nonvolatile solute of molar mass \(126 \mathrm{~g} \mathrm{~mol}^{-1}\) dissolved in \(80 \mathrm{~mL}\) water. \(\left[\right.\) Cryoscopic constant of water \(\left.=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right]\)

  1. A \(0.55 \mathrm{~K}\)
  2. B \(0.74 \mathrm{~K}\)
  3. C \(0.86 \mathrm{~K}\)
  4. D \(0.96 \mathrm{~K}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(0.74 \mathrm{~K}\)

Step-by-step Solution

Detailed explanation

\(80 \mathrm{~mL} \text { water }=80 \mathrm{~g} \text { water (Density of}\) \(\text{water }= 1 \mathrm{~g} / \mathrm{mL} \text { ) } \)
\( \Delta \mathrm{T}_{\mathrm{f}}=\frac{1000 \mathrm{~K}_{\mathrm{f}} \mathrm{W}_2}{\mathrm{M}_2 \mathrm{~W}_1} \)
\( =\frac{1000 \mathrm{~g} \mathrm{~kg}^{-1} \times 1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1} \times 4 \mathrm{~g}}{126 \mathrm{~g} \mathrm{~mol}^{-1} \times 80 \mathrm{~g}} \)
\( =0.74 \mathrm{~K}\)