1. A sample of 33.17 mg of chymotrypsin was dissolved in water and diluted to a

Question

1. A sample of 33.17 mg of chymotrypsin was dissolved in water and diluted to a total volume of 5.651 mL. The osmotic pressure of this solution at 25 C was 4.365 torr. What is the molar mass?

2. What is the vapor pressure above the solution prepared by mixing 72 g of ethylene dibromide with 45 g of propylene dibromide at 85 C? The vapor pressures of pure ethylene dibromide and propylene dibromide at 85 C are 170 torr and 127 torr respectively. These compounds form nearly ideal solutions when mixed together

Explanation / Answer

P = CRT

4.365 = ( 33.17 * 10^-3 / Mol mass ) / ( 5.651/1000) * 62.3637 * 298

Mol mass = 24991.0241 grams/mol

2)

Vapor pressure = sum of Pure pressur * mol fracn

Mol of ethylene bromide = 72/108.965 = 0.660

Mol of propylene bromide = 45/121 = 2.142

Mol fractn of ethylene bromide = 0.660 / ( 0.66 + 2.142) = 0.2355

Mol fractn of propenyl bromide = 1 - 0.2355 = 0.7645

Vapor pressure =

0.2355 * 170 +0.7645 *127

= 137.1265 torr

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