Page 146 - Bruno Linder Elementary Physical Chemistry

August 18, 2010 11:37 9in x 6in b985-appA Elementary Physical Chemistry

Appendix A: Homework Problem Sets 131

3
is K H =74.68 kPa m mol −1 . What is the solubility (molarity) of
oxygen in water at that temperature?
(b) If the minimum concentration of O 2 (g) in water necessary to sus-
tain life is 4 mg/L, what is the minimum partial pressure of O 2 (g)?
5. The vapor pressure of a pure solvent at 80.0 C is 400 Torr. When 0.15 g
◦
of a solute is dissolved in 6.5 g of this solvent, the pressure is reduced
by 15 Torr. The molar mass of the solvent is M solvent =80.0gmol −1 .
What is the molar mass, M solute of the compound?
6. The addition of 30.0g of a substance to 7.0 g of CCl 4 lowered the
freezing point of the solvent by 7.5 K. The freezing point lowering
constant is K f = 40 K/mol per 1 kg of solvent. What is the molar mass
of the compound?
7. The osmotic pressure of an aqueous solution of a solid in H 2 O(l)
is 125 kPa at 298.15K. The mass number of the solid is M =
180.16g mol −1 . The freezing point constant for water is K f =
1.86 Kkg solvent /mol solute . The normal freezing point of H 2 O(l) is
∗
T = 273.15 K. Calculate the freezing point of the solution.
f
8. Calculate the number of moles (the solubility) of CO 2 in water at
298.15 K when the partial pressure of CO 2 is
(a) 2.0 kP a ,
(b) 200 kP a.

Henry’s Law constant of CO 2 in water at 298.15K is K H =
3
2.937 kP a m mol −1 and the atmospheric pressure is 1 atm or 101 kPa
at 298.15 K.
3
9. Calculate the boiling point of 250 cm of water containing 7.5 g of
sucrose. The normal boiling point of water is 373.15K and the boiling
point elevation constant is K b =0.51 K kg mol −1 .
solv solute
10. (a) Solute B and solvent A form an ideal dilute solution. The partial
pressure of the solute is 30 Torr when the mole fraction of the solute
is x A =0.20. Find Henry’s Law constant K B.
(b) If the partial pressure of the solvent at that composition is 250 Torr,
what is the pressure of the pure solvent?
11. An aqueous solution containing a substance whose concentration is
7.50 g/L has an osmotic pressure of 1150 Torr at 77 K.
(a) What is the molecular weight of the solute?
◦
(b) What is the osmotic pressure of a solution at 27 Cthatcontains
1.00 g of this solute in 500 mL of solution?