5 Steps to a 5 AP Chemistry 2019

Solutions and Colligative Properties ❮ 191

❯ Answers and Explanations

1. C—If the solute is an electrolyte, the solu-
   tion will conduct electricity and the van’t Hoff
   factor, i, will be greater than 1. The choices do
   not include any conductivity measurements;
   therefore, the van’t Hoff factor would need to
   be determined. This determination may be 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. A—The potassium ion contribution from the
   KNO 3 is

()

















+

300.0 mL

1 mol KNO

1,000 mL

1 mol K

1 mol KNO

3

3

= 0.300 mole K+

The potassium ion contribution from K 3 PO 4 is

(^) ()














+

700.0 mL

2.0 mol K PO

1,000 mL

3 mol K

1 mol KPO

34

34

= 4.20 moles K+

The total potassium is 4.50 moles in a total

volume of 1.000 L. Thus, the potassium concen-

tration is 4.50 M.

15. A student prepares 100 mL of each of the fol-
    lowing solutions by dissolving the appropriate
    solute in water. He then proceeds to measure the
    electrical conductivity of each solution. Which of
    the following aqueous solutions has the greatest
    electrical conductivity?
    (A) 0.01 M Ba(OH) 2
    (B) 0.01 M KCl
    (C) 0.01 M Na 3 PO 4
    (D) 0.01 M HC 2 H 3 O 2

16. IONIC RADIUS (PM)

ION (CUBIC ENVIRONMENT)

Na+^132

Cd^2 + 124

La^3 + 130

The energy change in the following reaction is

the heat of hydration:

Mn+(g) + x H 2 O(l) → M(H 2 O)xn+(aq)

ΔH = Heat of hydration

In general, the heat of hydration is exothermic.

Assuming the value of x is the same in all cases,

which of the following correctly predicts the rela-

tive order of the heats of hydration for the ions

listed in the table and gives a correct explanation?

(A) Na+ > Cd^2 + > La^3 + because ions of elements

lower on the periodic table have lower hydra-

tion energies.

(B) Cd^2 +^ > La^3 +^ > Na+^ because smaller radii lead

to higher hydration energies.

(C) La^3 +^ > Cd^2 +^ > Na+^ because higher charges

lead to higher hydration energies.

(D) All are about the same because their ionic

radii are similar.