CL 351 Homework # 2
Due date: 18 August 2005
1. 20 cc of Ether and 100 cc of water, which are
mutually immiscible, are contacted in a container such that the interfacial
area is 12.2 cm2. Water forms the bottom layer being heavier than ether. An iodine-like solute is originally present
in both phases at 3 x 10-3 M.
However, it is 700 times more soluble in ether. Diffusion coefficients in both phases are
around 10-5 cm2/sec.
Resistance to mass transfer in the ether is across a 0.01 cm film; resistance
to mass transfer in the water involves a surface renewal time of 10
seconds. What is the solute
concentration in the ether after 20 minutes?
2. A packed, absorption tower was used to absorb
compound A from a gas mixture into solvent B.
At one point in the tower, the partial pressure of A in the gas stream
was 1.52 x 104 Pa and the concentration of A in the contacting
liquid stream was 1.0 x 10-3 kg mole/m3. The mass transfer between the gas stream and
the liquid stream at that point in the tower was 4 x 10-5 kg mole/(m2 sec).
The individual mass transfer coefficient on the gas side was 3.95 x 10-9
kg mole/(m2 sec Pa). A laboratory experiment verified that the
system satisfied Henry’s law and the liquid composition 1 x 10-3 kg
mole/m3 was in equilibrium with a partial pressure of 3.04 x 103
3. We are studying gas absorption into water at
2.2 atmospheres total pressure in a packed tower. From earlier experiments with ammonia and
methane, we believe that for both gases the mass transfer coefficient times the
packing area per tower volume is 18 lb mol/(hr ft3) for the gas side and 530 lb
mol/(hr ft3) for the liquid side. The
values for these two gases may be similar because methane and ammonia have
similar molecular weights. However,
their Henry’s law constants are different: 9.6 atmosphere for ammonia and
41,000 atmospheres for methane. What is
the overall gas-side mass transfer coefficient for each gas? What fraction of resistance does gas offer
for each gas?
4. A solution with oxygen dissolved in water
containing 0.5 mg oxygen per 100 grams of water is brought in contact with a
large volume of atmospheric air at 283 K and a total pressure of a1
atmosphere. The Henry’s law constant for
the oxygen-water system at 283 K equals 3.27 x 104 atm/mole fraction. Will the solution gain or lose oxygen? What will be the concentration of oxygen in
the final equilibrium solution?
5. Various met