A solution contains 57.0 g octane, C_8 C_16 (M = 114 g/mol) dissolved in 148 g o

Question

A solution contains 57.0 g octane, C_8 C_16 (M = 114 g/mol) dissolved in 148 g of benzene, C_6 H_4 (M = Octane is a nonelectrolyte. The freezing point of pure C_6 H_4 is 5.50 degree C; K_r for octane is 3.47 degree C/molal and the K_f for C_5 H_5 is 5.12 degree C/molal. The density of the solution is 0.83 g/mL. The molality of C_8 H_18 in the solution is m. a) 1.30 b) 0.500 c) 0.296 d) 3.38 e) 0.00338 The molality of the solution is M. a) 2.02 b) 0.494 c) 0.942 d) 2.80 e) indicate some other answer The freezing point of the solution is degree C. a) -1.18 b) -6.22 c) 2.94 d) -17.3 e) indicate some other answer degree C Which of the following substances exhibit hydrogen bonding? CH_3 (CH_2)_2 CH_2 OH CH_3 CH_2 CH_2 CH_3 CH_3 CH_2 NH_2 H_2 S a)1, 3, and 6 bj) 2 and 5 c) 3 and 6 d) 1, 4, and 6 e) 1, 3, 4, and 6

Explanation / Answer

1) molality of solution = number of moles / mass in kg

moles of C8H18 = 57 g / 114 g/mol = 0.5 moles

m = 0.5 moles / 0.148 kg = 3.38 mole/kg

2) molarity of solution = number of moles / volume in L

volume of solution = mass / density = (148 g /0.83 g/mL) = 178.3 mL

molarity = 0.5 moles / 0.1783 L = 2.8 mole/L

3) depression in freezing point

delta T = Kf . m

delta T = 5.12 C/molal x 3.38 mole/kg

delta T = 17.3056 C

T = 5.5 C - 17.3056 C = -11.8 C

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