PROPERTIES OF SOLUTIONS III
1. 25.0g sample of Mg(NO3)2 dissolves in 675mL of distilled water.
a. What is the boiling point elevation of the solution over that of the pure
solvent? Kb for water is 0.521kg K/mol or 0.521 K/m
b. At what temperature will the solution boil if the atmospheric pressure is
1.0atm?
2. What mass of KOH (in grams) must be dissolved in 350.0mL of distilled water
to raise the boiling point by 2.0ºC?
3. The van't Hoff factor for a 1.0M Ca(NO3)2 solution is greater than that of a
2.5M Ca(NO3)2 solution. Explain.
4. What mass of butanol (CH3CH2CH2CH2OH) must be added to 8746mL of
distilled water to depress the freezing point to -38.0ºC?
5. A 45.8g sample of an unknown alcohol is dissolved in 125mL of distilled water.
The freezing point of the solution is measured to be -21.3ºC.
a. Find the molality of the solution.
b. Find the number of moles of alcohol in the solution.
c. Find the molar mass of the unknown alcohol.
1985
The formula and the molecular weight of an unknown hydrocarbon compound are
to be determined by elemental analysis and the freezing point depression method.
a. The hydrocarbon is found to contain 93.46 percent carbon and 6.54 percent
hydrogen. Calculate the empirical formula of the unknown hydrocarbon.
b. A solution is prepared by dissolving 2.53 grams of p-dichlorobenzene
(molecular weight 147.0) in 25.86 grams of naphthalene (molecular weight
128.2). Calculate the molality of the p-dichlorobenzene solution.
c. The freezing point of pure naphthalene is determined to be 80.2°C. The
solution prepared in (b) is found to have an initial freezing point of 75.7°C.
Calculate the molal freezing-point depression constant of naphthalene.
d. A solution of 2.42 grams of the unknown hydrocarbon dissolved in 26.7
grams of naphthalene is found to freeze initially at 76.2°C. Calculate the
apparent molecular weight of the unknown hydrocarbon on the basis of the
freezing-point depression experiment above.
e. What is the molecular formula of the unknown hydrocarbon?
PROPERTIES OF SOLUTIONS III
1. 25.0g sample of Mg(NO3)2 dissolves in 675mL of distilled water.
a. What is the boiling point elevation of the solution over that of the pure
solvent? Kb for water is 0.521kg K/mol or 0.521 K/m
b. At what temperature will the solution boil if the atmospheric pressure is
1.0atm?
2. What mass of KOH (in grams) must be dissolved in 350.0mL of distilled water
to raise the boiling point by 2.0ºC?
3. The van't Hoff factor for a 1.0M Ca(NO3)2 solution is greater than that of a
2.5M Ca(NO3)2 solution. Explain.
4. What mass of butanol (CH3CH2CH2CH2OH) must be added to 8746mL of
distilled water to depress the freezing point to -38.0ºC?
5. A 45.8g sample of an unknown alcohol is dissolved in 125mL of distilled water.
The freezing point of the solution is measured to be -21.3ºC.
a. Find the molality of the solution.
b. Find the number of moles of alcohol in the solution.
c. Find the molar mass of the unknown alcohol.
1985
The formula and the molecular weight of an unknown hydrocarbon compound are
to be determined by elemental analysis and the freezing point depression method.
a. The hydrocarbon is found to contain 93.46 percent carbon and 6.54 percent
hydrogen. Calculate the empirical formula of the unknown hydrocarbon.
b. A solution is prepared by dissolving 2.53 grams of p-dichlorobenzene
(molecular weight 147.0) in 25.86 grams of naphthalene (molecular weight
128.2). Calculate the molality of the p-dichlorobenzene solution.
c. The freezing point of pure naphthalene is determined to be 80.2°C. The
solution prepared in (b) is found to have an initial freezing point of 75.7°C.
Calculate the molal freezing-point depression constant of naphthalene.
d. A solution of 2.42 grams of the unknown hydrocarbon dissolved in 26.7
grams of naphthalene is found to freeze initially at 76.2°C. Calculate the
apparent molecular weight of the unknown hydrocarbon on the basis of the
freezing-point depression experiment above.
e. What is the molecular formula of the unknown hydrocarbon?