# 2 Chem problems please help if you can?

1) Liquid A and liquid B form a solution that behaves ideally according to Raoult's Law. The vapor pressure of the pure substances A and B are 205 torr and 135 torr respectively. Determine the vapor pressure ober teh solution if 1.25 moles of liquid A is added to 5.30 moles of liquid B.

2) The freezing point for t-butanol is 25.50 degrees Celsius and Kr is 9.1 degrees Celsius/m. Usually t-butanol absorbs water on exosure to air. If the Freezing point of a 10.0g sample of t-butanol is measured as 24.59 degrees Celsius, how many grams of water is present in the sample?

1) Pa = P°a Xa and Pb = P°b Xb

Xa = 1.25 / 1.25 + 5.30 = 0.191

Pa = 205 x 0.191 = 39.1 torr

Xb = 5.30 / 1.25 + 5.30 = 0.809

Pb = 135 x 0.809 = 109.2 torr

2) delta T = 25.50 - 24.59 = 0.91

delta T = k x m

0.91 = 9.1 x m

m = 0.1

molar mass t-butanol = 74 g/mol

10.0 / 74 = 0.135 moles

m = 0.1 = 0.135 moles / Kg water

Kg water = 1.35 = 1350 g

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2) The freezing point for t-butanol is 25.50 degrees Celsius and Kr is 9.1 degrees Celsius/m. Usually t-butanol absorbs water on exosure to air. If the Freezing point of a 10.0g sample of t-butanol is measured as 24.59 degrees Celsius, how many grams of water is present in the sample?

**Answer:**1) Pa = P°a Xa and Pb = P°b Xb

Xa = 1.25 / 1.25 + 5.30 = 0.191

Pa = 205 x 0.191 = 39.1 torr

Xb = 5.30 / 1.25 + 5.30 = 0.809

Pb = 135 x 0.809 = 109.2 torr

2) delta T = 25.50 - 24.59 = 0.91

delta T = k x m

0.91 = 9.1 x m

m = 0.1

molar mass t-butanol = 74 g/mol

10.0 / 74 = 0.135 moles

m = 0.1 = 0.135 moles / Kg water

Kg water = 1.35 = 1350 g

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