Mass of beaker, test tube (g) Freezing point, from cooling curve (degree C) Inst

Question

Mass of beaker, test tube (g) Freezing point, from cooling curve (degree C) Instructor's approval of graph Freezing point of Cyclohexane plus Unknown Solute Mass of beaker, test tube, cyclohexane (g) Mass of cyclohexane (g) Tared mass of added solute (g) Freezing point, from cooling curve (degree C) Instructor's approval of graph k_f for cyclohexane (degree C kg/mol) Freezing point change Delta T^f (degree C). Mass of cyclohexane in solution (kg) Moles of solute, total (mol) Mass of solute in solution, total (g) Molar mass of solute (g/mol) Average molar mass of solute (g/mol) Standard deviation of molar mass Relative standard deviation of molar mass (% RSD)

Explanation / Answer

depression in F.P = kf*m

where m = molality = moles of the unknown solid/mass of cyclohexane in kgs

Let molar mass of the unknown solid be 'M' g/mole

Thus, moles of the unknown solid = mass/molar mass = 0.2029/M

molality = (0.2029/M)/0.0100055) = 20.2788/M

Thus, 2.56 = 20*(20.2788/M)

or, M = 158.43 g/mole

Thus, molar mas of the unknown solid = 158.43 g/mole

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