Question

When 10.5 g of a certain molecular compound X are dissolved in 75. g of benzonitrile (CAH,CN), the freezing point of the solution is measured to be -13.8 °C. Calculate the molar mass of X. If you need any additional information on benzonitrile, use only what you find in the ALEKS Data resource. Also, be sure your answer has a unit symbol, and is rounded to 1 significant digit. OP X 5

Answer 1

Answer :-
8 x 102(g/mol)
or
0.8(kg/mol)

Given :-

Freezing point of Benzonitrile = T⁰ = -12.82 °C

Freezing point of solution = T = -13.8 °C

Molal freezing point depression constant for Benzonitrile = K_f = 5.35 °C.kg/mol

Mass of Solute (unknown) = W₂ = 10.5 g = 0.0105 kg

Mass of Solvent = W₁ = 75 g = 0.075 kg

Freezing point depression =
AT: = 10-1

ie.
AT, = -12.82(C) - (-13.8(°C)) = 0.98(°C)

Molar mass of Solute (unknown) = M₂ = ?

Formula :-

M2 = ATX W1 M2 = Kg x W)

M2 = - 5.35("C.kg/mol) x 0.0105(kg) 0.98(°C) x 0.075(kg)

M2 = 0.7643(kg/mol) = 0.8(kg/mol)
(rounded to one significant digit)

or
M2 = 0.8 kg/mol) = 800(g/mol)

i.e.
M2 = 8 x 10P(g/mol)
(rounded to one significant digit)