12. (5 pts) An aqueous Caci2 (FM 110.98 g/mol)solution has a vapor pressure of 8

Question

12. (5 pts) An aqueous Caci2 (FM 110.98 g/mol)solution has a vapor pressure of 81.6 mmHg at 50.0 oC. The vapor pressure of pure water (FM 18.02 g/mol at this temperature is 92.6 mmHg. What is the concentration of CaCl2 in mass percent? CaCl 13. (4 pts) Consider the following reaction: 2 H2O2 *mmm 2H20 +o2 (a) If H202 is decomposing at the rate of 0.66 s, at what rate is O2 being formed? M/s (b) Assuming this is an elementary reaction (like all the ones discussed thus far), what is the rate law expression? Rate

Explanation / Answer

Q12

Apply colligative properties

dP = xsolute*Psolvent

so

dP = Pwater - Pmix = 92.6-81.6 = 11

so

dP = xsolute*Psolent

x solute = 11/(92.6) = 0.11879

so

x solut = mol of solute / (mol of solute + mol of solvnet)

assume

1 mol of water so..

0.11879 = S/(S+1)

0.11879S+ 0.11879 = S

(1-0.11879)S = 0.11879

S = (0.11879)/(1-0.11879) = 0.1348 mol of S

total mass of mix = S + water = 0.1348*110.98 + 1*18 = 32.96 g

mass of S =  0.1348*110.98 = 14.960104

so.

% S = 14.960104/(32.96*100 = 45.38%

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