AP CHEM
Integrative Colligative Questions
May 2011
1. When 0.55g of pure benzoic acid (C6H5COOH) is dissolved in 32.0g of benzene (C6H6), the
freezing point of the solution is 0.36°C lower than the freezing point value of 5.5°C for the
pure solvent. (a) Calculate the molecular weight of benzoic acid in benzene. (b) Use the
structure of the solute to account for the observed value?
O
OH
AP CHEM
Integrative Colligative Questions
May 2011
2. At 35°C the vapor pressure of acetone, (CH3)2CO , is 360 torr and that of chloroform, CHCl3 is
300 torr. Acetone and chloroform can form weak hydrogen bonds between one another as
follows:
Cl
CH3
Cl
H
Cl
O
CH3
A solution composed of equal number of moles of acetone and chloroform has a vapor
pressure of 250 torr at 35°C (a) What would the vapor pressure of the solution if it exhibited
ideal behavior? (b) Use the existence of hydrogen bonds between acetone and chloroform
molecules to explain the deviation from ideal behavior. (c) Based on the behavior of the solution predict whether the mixing of acetone and chloroform is an exothermic (∆Hsoln < 0) or endothermic ((∆Hsoln >0) process