DAT Mass of lauric acid Mass of benzoic acid Freezing temper

DAT Mass of lauric acid Mass of benzoic acid Freezing temperature of pure lauric acid LolG 2. 9 39.05 Freezing point of the benzoic acid-lauric acid mixture Freezing temperature depression, At 42939.0 5 5 \"C Molality, m molkg Moles of benzoic acid mol Molecular weight of benzoic acid (experimental) g/mol Molecular weight of benzoic acid (accepted g/mol Percent error 15-4 Chemistry with Computers

Solution

Change in temperature = 42.9 - 39.05 = 3.85 degree C

Kf of lauric acid = 3.9 ⁰C.kg/mol

We know,

depression infreezing point = Kf * molality

Molality = 3.85 / 3.90

Molality = 0.987 mol /kg.

But molality = moles of solute / mass of solvent in kg

0.987 = moles of solute / 0.008006

Moles of solute = 0.00790 mol

Molecular weight of benzoic acid = mass of benzoic acid / moles of benzoic acid

Molecular weight f bezoic acid = 1.016 / 0.00790 = 128.6 g/mol

Accepted molecular weigth of benzoic acid, C6H5COOH = 84 + 6 + 32 = 122 g/mol

% Error = ( 128.6 - 122 ) * 100 / 122 = 5.41 %