Pure CS2 melts at -112°C. 228 grams of propylene glycol crystals is mixed with 500 grams of CS2. If kf of CS2 = -3.83 K kg mol^-1 what is the depression in freezing point?(a) -23°C(b) -135°C(c) -20°C(d) -100°CThis question was posed to me in exam.The origin of the question is Colligative Properties and Determination of Molar Mass topic in portion Solutions of Chemistry – Class 12

Pure CS2 melts at -112°C. 228 grams of propylene glycol crystals is m

1.	Pure CS2 melts at -112°C. 228 grams of propylene glycol crystals is mixed with 500 grams of CS2. If kf of CS2 = -3.83 K kg mol^-1 what is the depression in freezing point?(a) -23°C(b) -135°C(c) -20°C(d) -100°CThis question was posed to me in exam.The origin of the question is Colligative Properties and Determination of Molar Mass topic in portion Solutions of Chemistry – Class 12
Answer» The correct option is (a) -23°C The best I can explain: Given, kf = -3.83 k kg mol^-1 MASS of solute, w2 = 228 g Mass of solvent, W1 = 500 g Molar mass of solute, M2 = 76 g/mole Moles of solute = w2/M2 = 228/76 = 3 moles Molality of the solution, m = Number of moles of solute/mass of solvent (kg) m = 3 moles/0.5 kg = 6 molal We know, ΔTf = kf x m ΔTf = -3.83 x 6 = -23°C.

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