Chemistry II
Worksheet
Colligative Properties 1
1. Define each of the following terms:
a. electrolyte
b. colligative property
c. saturated solution
2. Calculate the molality of 25.0 grams of KBr dissolved in 750.0 mL of pure water. What is “i” for this
solute? (ρH2O=1 g/mL)
3. 80.0 grams of glucose (C6H12O6, mol. mass = 180. g/mol) is dissolved in 1.00 kg of water. Calculate
the molality. What is “i” for this solute?
4. Calculate the molality when 75.0 grams of MgCl2 is dissolved in 500.0 g of solvent. What is “i” for
this solute?
5. The freezing point and electrical conductivities of three aqueous solutions are given below. (Kf = –
1.86°C/m)
Solution
Freezing
Electrical
(0.010 molal)
Point
Conductivity
sucrose
-0.0186˚C
almost zero
acetic acid
-0.0213˚C
low
sodium chloride
-0.0361˚C
high
Explain the relationship between the freezing point and electrical conductivity for each of the
solutions above. Account for the differences in the freezing points among the three solutions.
6. Explain, in your own words, why the addition of sucrose to water will result in an increase in the
boiling point of the solution.
Use the table for the following problems.
substance
Kf (°°C/m)
benzene
5.12
carbon tetrachloride
30.
water
1.853
Kb (°°C/m)
2.53
5.03
0.515
7. Seawater is about 3.5% (by weight) dissolved solids, almost all of which is NaCl. Calculate the normal
boiling point of seawater.
8. 0.64 g of adrenaline in 36.0 g of CCl4 produces a bp elevation of 0.49 °C. What is adrenaline's
molecular weight.
9. Calculate the freezing point of a solution of 5.00 g of diphenyl, C12H10, and 7.50 g of naphthalene,
C10H8, dissolved in 200.0 g of benzene (fp = 5.5 °C)
Answers
1. See your notes and text!
2. 0.280 m, i = 2
3. 0.444 m, i = 1
4. 1.15 m, i = 3
5. sucrose
a non electrolyte
0.010 mol/kg lowers freezing point 0.0186˚C
acetic acid
a weak electrolyte; low conductance as a result of low ion concentration
mtotal > 0.010 molal due to partial ionization and ∆Tf somewhat greater than 0.0186˚C
sodium chloride
a salt and strong electrolyte
approximately 100% dissociation into ions, mtotal approaching 0.02 molal
6.
7.
8.
9.
See your notes! Use a phase diagram as part of your answers!
100.64 °C
182 g/mol
3.2 °C