Cliffs AP Chemistry, 3rd Edition

Figure 4

Figure 5

Analysis:

1. What was the freezing point of the solution?
   The intersection of the two lines occurred at approximately 48.4 °C


2. What was the freezing point depression of the solution? The standard freezing point for
   paradichlorobenzene is 53.0°C.

∆Tf= T°f−Tf= 53.0 °C −48.4 °C = 4.6 °C

3. What was the molality of the naphthalene? The freezing point depression constant for

paradichlorobenzene is 7.1 °C ⋅m–1.

.

.

m.

k

T

Cm

∆ C 065 m

71

46

f

f

o

o

= ==: - 1

4. What was the molecular mass of naphthalene?

..

..

MM kg solvent T

k g solute

mol kg C

Ckg g

∆ 0 0520 4 6 g mol

71 40

solute f 120

f

o

o

1

:

:

::

::

== =: -

5. What was the percent error of the results compared to the actual molecular mass of

128 g ⋅mol–1?

% exp %%%

exp

error ected

observed ected

===-## 100 120 128 128 100 6

• 
  
  
  
  • 
    
  
  
  
  

The results were about 6% below expected.

Temperature

°C

Time (min)

1

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Freezing Point Depression of Naphthalene in Paradichlorobenzene

Naphthalene, C 10 H 8

Laboratory Experiments