Name _______________Key_______________________________ Colligative Properties
Molality (m)= moles of solute/ kilogram of solvent
The molal freezing point constant for water (Kf) = -1.86 °C/m
ΔTf = Kf × m × i
ΔTb = Kb × m × i
The molal boiling point constant for water (Kb) = 0.51 °C/m
i = number of moles of particles produced per mole of solute
1.
Which of the following solutions would have the lowest freezing point?
a. 0.3 m NaCl
b. 0.3 m CaCl2
c. 0.3 m AlCl3
d. 0.3 m C6H12O6
2.
Which of the following solutions would have a freezing point most similar to a 1.0 m CaCl2 solution?
a. 1.0 m NaCl
b. 1.0 m AlCl3
c. 1.0 m C12H22O11
d. 1.0 m Na2CO3
3.
Which of the following would have a boiling point elevation most similar to that of a 0.2 m NaCl solution?
a. 0.4 m C12H22O11
b. 0.2 m C12H22O11
c. 0.1 m C12H22O11
d. 0.1 m NaCl
4.
Which of the following solutions would have an osmotic pressure most similar to that of a 4.0 m C12H22O11 solution?
a. 4.0 m NaCl
b. 1.0 m Na3PO4
c. 2 m CaCl2
d. 2 m C6H12O6
5.
Which of the following would have a freezing point closest to that of pure water?
a. 1.0 m NaCl
b. 1.0 m CaCl2
c. 1.0 m C12H22O11
d. 1.0 m Cu3(PO4)2
6.
When would a chemist use molality instead of molarity? (Page 422-423)
7.
If 1.00 mole of NaOH is dissolved in 1000 grams of water, what is the molality of this solution? 1 m
8.
What is the molality of a solution that has 40 grams of NaOH dissolved in 1.00 kilogram of water? 1 m
9.
If 80.0 grams of NaOH is dissolved in 1 kg of water, what is the molality of this solution?
Look it up!
2m
10. What is the molality of a solution that has 58.45 grams of NaCl dissolved in 500.0 grams of water. (NaCl= 58.45 g/mol)
2.000 m
11. A solution was prepared by dissolving 342 grams of table sugar (sucrose), C12H22O11, in 2000 grams of water. Find the
molal concentration of this solution. (molar mass of C12H22O11 = 342 g/mol)
0.5 m
12. If 29.2 grams of table salt (NaCl) is dissolved in 500 grams of water, what is the molality of this solution?
(NaCl= 58.4 g/mol)
1m
13. What is the boiling point of a solution made by dissolving 1.0000 mole of sucrose (C12H22O11) in 1.0000 kilogram of water?
100.51 ̊ C
14. What is the freezing point of a solution made by dissolving 342 grams of table sugar (C12H22O11) in 1000.0 grams of water?
-1.86 ̊ C
15. A solution is made by dissolving 58.45 grams of NaCl in 1000.0 grams of water. At what temperature will this solution
freeze? (NaCl= 58.45 g/mol)
-3.720 ̊ C
16. At what temperature will the solution in # 15 above boil? 101.02 ̊ C
17. How many grams of sodium chloride must be dissolved in 3000.0 grams of water so that it will boil at 105 °C?
860 grams, but to get correct sig. fig.’s it would be 8.60 X 102 grams
18. How many grams of sodium chloride must be dissolved in 3000.0 grams of water so that the solution freezes at -5.00 °C?
236 grams NaCl
19. Which will have the lowest freezing point— 50.0 grams of sucrose in 1000.0 grams of water
or
25.0 grams of NaCl
in 1000.0 grams of water?
They are not the same! The concentrations are given in grams, not moles! So convert to moles first! The NaCl should have the
lowest freezing point at -1.60 C
̊ compared to the sucrose at -0.279 ̊C
20. What is the definition of a colligative property from page 446 in your text? Look it up!