2- A 7.80 g sample of a nonvolatile nonelectrolyte blue crystalline solid is dis

Question

2- A 7.80 g sample of a nonvolatile nonelectrolyte blue crystalline solid is dissolved in 31.8 g of acetic acid, producing a solution that bolis at 119.5oC. Find the molar mass of the blue solid in g/mol.

A 7.80 g sample of a nonvolatile nonelectrolyte blue crystalline solid is dissolved in 31.8 g of acetic acid, producing a solution that bolis at 119.5°C. Find the molar mass of the blue solid in g/mol TABLE 12.3 Bolling-Point Elevations and Freezing-Point Depression Constants for Solvents Boiling Point(°C) 117.90 80.10 (oCim) Freezing Point (C) k, Solvent 8.07 2.53 Acetic acid Benzene Naphthalene Water 8.90 4.90 6.8 1.86 16.60 5.51 80.2 100.0 0.512 0.00

Explanation / Answer

We know that T f = Kf x m
Where

T f = elevation in boiling point

        = boiling point of solution - boiling point of solvent

        = 119.5 - 117.90 oC

        = 1.6 oC

K f = elevation in boiling point constant of acetic acid = 3.07 oC/m

m = molality of the solution

    = ( mass / Molar mass ) / weight of the solvent in Kg

    = (7.80 /M) / 0.0318 kg

   = 245.3 /M

Plug the values we get 1.6 = 3.07x(245.3/M)

                                   M = 470.7 g/mol

Therefore the molar mass of the blue solid is 470.7 g/mol

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