Molality and the Colligative Properties of Solutions
Do not write on this worksheet.
Concept Review
1. What are colligative properties?
2. Define the term “molality.”
3. Normal freezing points depress. What does this mean?
4. Normal boiling points elevate. What does this mean?
5. The density of water is 1.0 g/mL.
6. What is the volume of 1,000 g of water?
7. What is the volume of 1.0 kg of water?
8. What is the mass of 1,000 mL of water?
9. What is the mass of 1.0 L of water?
10. What conversion factor exists between kg of water and L of water?
Molality Calculation
Determine the molality (m) of the following aqueous solutions.
11.
12.
13.
14.
15.
16.
17.
67.99 g Mg(OH)2 in 750 mL water [1.55 49 m ≈ 1.6 m]
100 g KI in 1000 mL water [0.6024 m≈ 0.6 m]
80.0 g KCl in 500.0 mL water [2.1447 m ≈ 2.14 m]
10.0 g NaClO in 135 mL water [0.9942 m ≈ 0.994 m]
750 g NaCl in 2500 mL water [5.128 m ≈ 5.1 m]
What is the molality of a solution of NH4NO3 contains 2.05 g of solute in 252 g of water? [0.1016 m ≈ 0.102 m]
A solution of NaNO3 contains 34.0 g solute dissolved in 100.00 g water. What is the solution's molality? [4 m ≈ 4.00
m]
18. What is the molality of a 10.5-gram sample of NaCl dissolves in 500 grams of water? [ 0.3589 m ≈ 0.4 m]
19. A 14.5-gram sample of potassium sulfate (K2SO4) dissolves in 677 mL of water. What is the molality of the solution?
(The density of water is 1.00 g/mL). [0.1228 m ≈ 0.1 m]
Freezing Point Depression
and
Solvent
water
Tf (oC)
Kf (ºC/molal)
0.0
1.86
Solvent
benzene
Tf (oC)
Kf (ºC/molal)
5.5
5.12
20. What is the freezing point of a solution dissolved in water if the concentration of the solution is 0.24 m? [ ]
21. What is the freezing point of a 0.850 m aqueous solution of sugar? [ ]
22. What is the freezing point of a solution that contains 68.4 g of sucrose dissolved in 100.0 g water? [ ]
23. If 13.4 g of the scopolamine (C17H21NO4) is dissolved in 50.3 g of water, what will become the solution’s freezing
point? [m = 0.8792131 m ΔTf = 1.64 oC and FPnew = -1.64 oC]
24. What is the freezing point depression when 85.3 g of oxygen gas is dissolved in 1,500 g of water? [m = 1.777083 m
ΔTf = 3.3 oC and FPnew = -3.3 oC]
SC7. Students will characterize the properties that describe solutions and the nature of acids and bases.
a. Explain the process of dissolving in terms of solute/solvent interactions (iv.) relate molality to colligative properties.
 You exceeded the standard(s).
 You met the standard(s).
 You did not meet the standard(s).
Molality and the Colligative Properties of Solutions
Do not write on this worksheet.
25. What is the freezing point of 1050 g of benzene if 31.1 g of orcinol (C7H8O2) is dissolved in the benzene? [m =
0.2388632m ΔTf = 1.2229 oC and FPnew = -1.22 oC]
26. What will become the freezing point of 42.0 g of ibuprofen (C13H18O2) when it is dissolved in 975 g of benzene? [ ]
Boiling Point Depression
and
Solvent
water
Tb (oC)
Kb (ºC/molal)
100.0
0.52
Solvent
benzene
Tb (oC)
Kb (ºC/molal)
80.1
2.67
27. What is the boiling point of a solution dissolved in water if the concentration of the solution is
0.24 m? [ ]
28. What is the boiling point of a 0.850 m aqueous solution of sugar? [ ]
29. What is the boiling point of a solution that contains 68.4 g of sucrose dissolved in 100.0 g water? [ ]
30. What is the boiling point when 11.4 g of ammonia (NH3) is dissolved in 200 g of H2O? [m = 3.3529411 m
and BPnew = 102 oC]
31. If 67.7 g of urea (CH4N2O) is dissolved in 833 g of benzene, what is the new boiling point? [ ]
32. What is the boiling point when 31.5 g of menthol (C10H20O) is dissolved in 258 g of benzene? [ ]
SC7. Students will characterize the properties that describe solutions and the nature of acids and bases.
a. Explain the process of dissolving in terms of solute/solvent interactions (iv.) relate molality to colligative properties.
 You exceeded the standard(s).
 You met the standard(s).
 You did not meet the standard(s).
ΔTb = 2 oC