Los Angeles City College Chemistry 60
Additional Practice Problems: Colligative Properties and Stoichiometry (with Answers)
H
2
O, the resulting solution has a freezing point of -0.227 ºC.
A.
What is the molar mass of riboflavin? 376.9 g/mol
B.
What is the molecular formula of riboflavin if combustion analysis shows it to consist of 54.25% C, 5.36% H, 25.50% O, and 14.89% N? C
17
H
20
O
6
N
4
2. Creatinine is a by-product of nitrogen metabolism and can be used to provide an indication of renal function. A 4.04 g sample of creatinine is dissolved in enough water to make 100.0 mL of solution. The osmotic pressure of the solution is 8.73 mm Hg at
298 K. What is the molar mass of creatinine? 8.60 x 10
4
g/mol
3. What mass (in g) of a nonelectrolytic molecular substance (MW = 50.0 g/mol) must be added to 500 g of water to produce a solution that boils at 101.56 ºC? 75.0 g
4.
Nicotine, extracted from tobacco leaves, is a liquid completely miscible with water at temperatures below 60 ºC.
A.
What is the molality of nicotine in an aqueous solution that starts to freeze at
-0.450 ºC? 0.242 m
B.
If this solution is obtained by dissolving 1.921 g of nicotine in 48.92 g of H
2
O, what must be the molar mass (in g/mol) of nicotine? 162.3 g/mol
C.
Combustion analysis shows nicotine to consist of 74.03% C, 8.70% H, and
17.27% N by mass. What is the MOLECULAR formula of nicotine? C
10
H
14
N
2
5. A 50.00 mL sample of an aqueous solution contains 1.08 g of human serum albumin, a blood plasma protein. The solution has an osmotic pressure of 5.85 mm Hg at 25 ºC.
What is the molar mass (in g/mol) of the albumin? 6.86 x 10
4
g/mol