• Heat the water to the boiling point, and record the temperature of the water to the
  nearest 0.5°C.


• Do not let thermometer touch sides or bottom of flask.


• Be sure temperature is constant when reading.


• Prepare a solution of 10.0 grams of KNO 3 in 50.0 grams of distilled water. May
  have to add more water to the Erlenmeyer due to loss by evaporation.


• Determine B.P. of this solution.
  (c)Restatement: Formula mass of solute.


• Change in boiling point
  change in B.P. = B.P. of solution −B.P. of solvent
  = 102.2°C −100.0°C = 2.2°C


• Molal concentration of solution

.

..

i C

change in B P temperature

kg

mole

052 1

#^1

`j%

where i= 2 because two moles of ions are formed for each mole of KNO 3 used.

.

.

.

/

C

C

kg

(^221) mole 21 moles kg
2052 1

=

%
`j%

• Formula mass of KNO 3
  .
  grams of solvent

grams of solute

moles solute

10 10^3 g water

#

#

.

.

.

.

gH O /

g KNO

moles KNO

gH O

50 0 gmole

10 0

21

10 10

95

3

2

3

3

2

#

#

=

(d)Restatement: Calculate the % error and possible sources.

KNO 3 formula mass (theoretical) = 101 g/mole

KNO 3 formula mass (from data) = 95 g/mole

%

values

error theoretical value 100 %

difference between theoretical and experimental

= #

%%error=101 95 101 - # 100 = 6 %

Sources of Error: 1. Experimental error in measurement; 2. Measuring tools not reliable or not
sensitive enough; 3. Activity of ions as proposed by Debye and Huckel which states an “effec-
tive” concentration called activity which takes into account interionic attractions resulting in a
decrease in the magnitude of colligative properties, especially for concentrated solutions.

Part II: Specific Topics