PROBLEMS
(In this set of problems assume that all the solutes are molecular.)
1. When 92 grams of a compound are dissolved in 2000 grams of water here is a lowering of the freezing -point to -1.86°C.
What is its molecular weight?
2. When 31 grams of a compound are dissolved in 500 grams of water, the freezing-point is -1.86°C. Calculate its molecular
weight. (Hint: as a general rule, solve first for the molal concentration.)
3: If 2.00 moles of glycerol, C3H5(OH)3, are dissolved in 1000 grams of water, what , would be the freezing-point?
4. Thirty grams of a nonvolatile solute are dissolved in 1000 g of water at 760 mm pressure. The solution boils at 100.17 C.
Determine the molecular weight.
5. If 5.000 moles of a nonvolatile compound are added to 500 g of H20, what is the boiling-point of the solution at 1
atmosphere pressure?
6. A quantity of a nonvolatile solute was dissolved in 200 grams of water. The boiling-point of the solution was 101.275 °C at
760 mm pressure. How many moles of the solute were used?
7. When 4.6 grams of a compound were dissolved in 50 grams of water, the resulting solution was found to have a
freezing-point of -3.72°C. Calculate the molecular weight of the compound.
8. When 6.0 g of a molecular compound were dissolved in 40 g of H20, the freezing-point of the solution was found to be
-4.65°C. Calculate the molecular weight of the compound.
9. Calculate the molecular weight of urea, 180 grams of which dissolve in 1500 grams of water to produce a solution having a
freezing-point of --3.72°C.
10. When 4.70 g of a nonvolatile compound are dissolved in 50.0 g of water, the resulting solution boils at 100.34°C at 760 mm
pressure. Calculate the molecular weight of the compound.
11. When 124 grams of the alcohol, ethylene glycol, are dissolved in 1000 grams of water, the freezing-point is - 3.72 C. (a) Calculate
the molecular weight of it. Upon analysis it is found to contain carbon = 38.7%, hydrogen = 9.7%, and oxygen = 51.6%. (b)
Calculate its empirical formula and (c) its correct molecular formula.
12 .Calculate the weight of methanol, CH30H, required to lower the freezing-point of 10.00 liters of water to - 20.00°e.
13
.When 171 g of a sugar are dissolved in 250 g H 20, the boiling-point of the solution is 101.02°C at one atmosphere pressure.
Calculate the molecular weight of the sugar.
14. What weight of dextrose, CGH1206, dissolved in 2000 grams of water, will raise the boiling-point to 102.04°C at one atmosphere
pressure?
15
.Calculate the molecular weight of propyl alcohol, 10 grams of which dissolve in 500 grams of water to lower the freezing-point by
0.62Co.
16. If 9.2 grams of a molecular compound are dissolved in 200 grams of water, the freezing-point is -0.93°C. Calculate the molecular
weight of the solute.
17. Calculate the freezing-point of a solution prepared by dissolving 1000 grams of methanol in 4.00 liters of water.
18. When 1.28 grams of sulfur are dissolved in 10 grams of naphthalene, its freezing-point is 76.75°e. The freezing-point of pure
naphthalene is 80.2°C and its molal freezing-point depression constant is 6.9Co. (a) Calculate the molecular weight of the sulfur
used, and (b) what is the molecular formula of the sulfur?
19. Calculate the freezing-point of a water solution which is 30.0% by weight ethyl alcohol (M. W. = 46).
In 20 and 21 assume the normal freezing-point of benzene is 5.50°C and its molal freezing-point depression constant is 5.10 C.
20. In a molecular-weight determination, it was found that a solution of 1.200 grams of the compound paranitrotoluene in 10.00 grams
of benzene has a freezing point of 1.03°C. Calculate the molecular weight of the compound.
21. When 0.441 gram of an organic compound, thought to be paradichlorobenzene, was dissolved in 10.0 grams of benzene, the
freezing point of the solution was found to be 3.97°C. The compound was analyzed and found to contain by weight 49.0% carbon,
2.7% hydrogen, and 48.3% chlorine. Calculate the (a) molecular weight, (b) simplest formula, and (c) correct molecular formula
for the compound.