Calculations for Expt. 23

Colligative Properties

Part A : Objective: To determine the freezing point of the solvent naphthalene

Mass of naphthalene used = (Mass of test tube + naphthalene) – (Mass of empty test tube)

Freezing Point of naphthalene = is the temperature at longest plateau (flat line) on the graph

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Part B: Objective: To determine the Kf (freezing pt. dissociation constant) of naphthalene

Freezing Point naphthalene/dichlorobenzene solution = is the temperature at longest plateau (flat line) on the SECOND graph (should be below the first freezing point)

DT (Change in Freezing Point) = the Freezing Point of naphthalene (Graph A) minus Freezing Point naphthalene/dichlorobenzene solution (Graph B)

Moles of 1,4-dichlorobenzene = grams of 1,4-dichlorobenzene used

Molar mass of 1,4-dichlorobenzene which is 147 grams/mole

Molality of dichlorobenzene solution = Mole of 1,4-dichlorobenzene

Kg of solvent which is naphthalene

If DT = iKf x molality, then: Kf for naphthalene = ______DT ______

Molality of diclorobenzene solution

[Note that i = 1 in this experiment.]

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Part C: Objective: To determine the molar mass of sulfur

Freezing point of naphthalene/sulfur solution = is the temperature at longest plateau (flat line) on the THIRD graph (Please note that third graph should fall between first and second graph.)

DT = Freezing Pt. Part A minus Freezing Pt. Part C

Again, if DT = iKf x molality, then:

Molality of sulfur solution = ______DT

Calculated Kf from Part B

Moles of sulfur in the solution = Molality of sulfur solution x Kg. of naphthalene solvent in Part C

Calculated Molar Mass of Sulfur = grams of sulfur used

# moles of sulfur in solution

Ratio = calculated molar mass of sulfur

32 gm/mole

Molecular Formula = S Ratio

% Error in Calculated Molar Mass of Sulfur = 256gm/mole - calculated molar mass of sulfur x 100

256 gm/mole