12.6 Steam Distillation
1. The steam distillation is used in the phenylamine purification :
a. Explain why phenylamine cannot be distilled by the normal distillation method.
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b. A mixture of phenylamine (boiling point = 185 C ) and water boils at 98 C at atmospheric pressure (101.3 kPa). At 98 C ,
the vapour pressures of phenylamine and water are respectively 7.07 kPa and 94.23 kPa.
i. Explain why that mixture boils at the temperature which is far below the boiling point of phenylamine.
ii. Calculate the percentage by mass of phenylamine in the distillate.
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iii. Steam distillation of bromobenzene yields a mixture that boils at 95 C and the distillate contains 62.1% of bromobenzene.
Give two reasons why % of bromobenzene in that distillate is different from the % of phenylamine in (b)(ii).
2. From the following data, calculate
the maximum mass of bromobenzene
(C6H5Br) that can be steam distilled
using 1000g of steam, assume that the
atmospheric pressure, 760 mmHg.
What is the temperature of this steam
distillation?
Temperature/
o
C
Vapour pressure in
mmHg
Water Bromobenzene
90
526
98
92
567
106
94
611
114
96
658
123
98
707
132
100
760
141
(H = 1; C = 12; O = 16; Br = 80)
Then, calculate the mass of bromobenzene
in the distillate.
Plot a graph of vapour pressure (mmHg) –
temperature (oC).
3.(a) The vapour pressure against
temperature graph for two
immiscible liquids P and Q is shown
below :
(i) On the grid, sketch a curve you
would expected to obtain for the
total vapour pressure of a
mixture of P and Q.
[2]
4. (a) The graph below shows how the
vapour pressures of a mixture of
organic compound, X (which is not
miscible with water) and water
changes with increasing in
temperature. On the same graph,
plot a graph of vapour pressure of X
against temperature.
(ii) Determine, until the nearest 0C ,
temperature when a mixture of P
and Q is distilled at standard
atmospheric pressure.
[1]
(b) A mixture containing 10g of organic
compound X in 100 cm3 water is
distilled at pressure 101 kPa for one
hour. The distillate is found to
contain 5.12 g X and 10.67 g water.
(iii) If the relative molecular mass of P
and Q are respectively 18.0 and
93.0, calculate the percentage of
Q by mass that you would expected
in the distillate in (a)(ii).
[3]
(iv) State a suitable type of distillation
for
a mixture of P and Q.
Explain the properties of P and Q
that
causes the type of distillation that
you
stated it is suitable for the mixture.
[2]
(i) Based on the above graph,
determine the vapour pressure of X
at the boiling point of the mixture.
(ii) Determine the mole ratio of X to
water in the vapour phase.
(iii) Determine the relative molecular
mass of X.
(iv) State the name of distillation
process used for the above
mixture.
(v) State one industrial application of
this distillation process. Explain
your answer.