5 Steps to a 5 AP Chemistry

18.Which of the following aqueous solutions would
have the greatest conductivity?

(A) 0.2 M NaOH

(B) 0.2 M RbCl

(C) 0.2 M NH 4 NO 3

(D) 0.2 M HNO 2

(E) 0.2 M K 3 PO 4

19.An aqueous KNO 3 solution is cooled from 75°C
to 15°C. Which statement from the following list
is true?

(A) The molarity of the solution does not

change.

(B) The molality of the solution decreases.

(C) The density of the solution does not change.

(D) The molality of the solution does not

change.

(E) The mole fraction of the solute increases.

20.How many milliliters of water must be added to
50.0 mL of 10.0 M HNO 3 to prepare 4.00 M HNO 3?

(A) 50.0 mL

(B) 125 mL

(C) 500 mL

(D) 250 mL

(E) 75.0 mL

21.Pick the pair of substances that will most likely

obey Raoult’s law.

(A) CH 3 CH 2 CH 2 CH 2 COOH(l) and C 5 H 12 (l)

(B) C 5 H 12 (l) and H 2 O(l)

(C) CH 3 CH 2 CH 2 CH 2 COOH(l) and H 2 O(l)

(D) H 3 PO 4 (l) and H 2 O(l)

(E) C 5 Hl2(l) and C 6 H 14 (l)

22.The best method to isolate pure MgSO 4 from an

aqueous solution of MgSO 4 is

(A) Evaporate the solution to dryness.

(B) Titrate the solution.

(C) Electrolyze the solution.

(D) Use paper chromatography.

(E) Filter the solution.

23.Pick the conditions that would yield the highest

concentration of N 2 (g) in water.

(A) partial pressure of gas =1.0 atm; tempera-

ture of water = 25 °C

(B) partial pressure of gas =0.50 atm; tempera-

ture of water = 55 °C

(C) partial pressure of gas =2.0 atm; tempera-

ture of water = 25 °C

(D) partial pressure of gas =2.0 atm; tempera-

ture of water = 85 °C

(E) partial pressure of gas =1.0 atm; temperature

of water = 85 °C

Solutions and Colligative Properties  191

 Answers and Explanations

1. C—If the solute is an electrolyte, the solution
   will conduct electricity and the van’t Hoff factor,
   i, will be greater than 1. The choices do not
   include any conductivity measurements; there-
   fore, the van’t Hoff factor would need to be deter-
   mined. This determination is done by measuring
   the osmotic pressure, the boiling-point elevation,
   or the freezing-point depression. The freezing-
   point depression may be found by measuring the
   freezing point of the solution.
   2. E—The potassium ion contribution from the
   KNO 3 is:

(300.0 mL)(1.0 mol KNO 3 /1000 mL)(l mol K+/

1 mol KNO 3 )

=0.300 mol K+

The potassium ion contribution from K 3 PO 4 is:

(700.0 mL)(2.0 mol K 3 PO 4 /l000 mL)(3 mol K+/

l mol K 3 PO 4 )

=4.20 mol K+

The total potassium is 4.50 mol in a total volume

of 1.000 L. Thus, the potassium concentration is

4.50 M.