A compound was found to be composed of the following amounts of elements: 20.00% wt% C, 26.64wt% O, 46.65 wt%N, and 6.71wt%H. A 6.125 grams sample of this compound dissolved in 46.205 grams of water as a solution was found to have a freezing point of -3.260C. The density of this solution was 1.066g/mL. Given that the freezing point depression constant and boiling point elevation constan for water are 1.766C/m and .512C/m, respectively answer the following questions.
a) calculate the molality (m) of this solution if the solute is a nonelectrolyte (i=1)
b) calculate of molarity (M) of this solution
c) the boiling point of the above solution
d) calculate the molecular mass of the dissolved solute
e) determine the empirical and molecular formula of the solute

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asked by lucy
  1. a. 3.26 = Kf*m
    Solve for m; I estimate 1.9 based on Kf = 1.766 (You may want to check that number).

    b. m = about 1.9 = mols/kg solvent
    1.9 = mols/0.046205; mols = about 0.085 mols.
    volume of 46.205 mL obtained from density. m = v x d; v = m/d = 46.205/1.066 = about 43.3 mL
    So M = mols/L = about 1.9/0.0433 = ?

    c. delta T = Kb*m. You have m from above.
    d. mol = g/molar mass. You have grams in the problem and mols from b which lets you solve for molar mass (but I don't believe the number you will get).
    mols C = 20/12 = ?
    mols O = 26.64/16 = ?
    mols N = 46.65/14 = ?
    mols H = 6.71/1 = ?
    Find the ratio of the mols to each other. I obtain COH4N2 (probably urea) but part d doesn't fit with this.

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