The molar mass of an unknown Organic compound was studied by a Freezing Point De

Question

The molar mass of an unknown Organic compound was studied by a Freezing Point Depression experiment. 0.455 g of the unknown compound was dissolved in 10.0 grams of CCl4. The freezing temperature of this mixture was -38.6 oC. Using the following data, what is the molar mass of this unknown Organic compound? Tf(CCl4) = -22.9 oC and Kf(CCl4) = 29.9 oC.

Answer Choices:

a) 21.4 g/mol                          b) 1.03 x 104 g/mol                             c) 2.14 x 103 g/mol

            d) 86.7 g/mol                          e) 418 g/mol

I need to the see the steps to solving this...

Explanation / Answer

1) Determine temperature change:

-22.9 - (-38.6) = 15.7 °C

2) Determine how many moles of the compound dissolved:

T = Kf m

15.7 °C = (29.9 °C kg mol-1) (x / 0.455 kg)

x = 0.2389 mol

3) Determine molecular weight:

10.0 g / 0.2389 mol = 41.8 g/mol

Ans is option (e) but it should be 41.8 g/mol instead of 418 g/mol

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