Solutions 2 Flashcards
state henry’s law
at a constant temperature, the
solubility of a gas in a liquid
is directly proportional to the
partial pressure of the gas
present above the surface of
liquid or solution.
The mass of gas dissolved in a given volume of liquid at a constant temperature is directly proportional to the pressure of the gas present in equilibirum with the liquid.
m = Kp
m mass
K constant
p pressure
state henry’s law in term of partial pressure
“the partial pressure of the gas
in vapour phase (p) is proportional to the mole fraction
of the gas (x) in the solution” and is expressed as:
p = KH x
Here KH
is the Henry’s law constant.
describe the characteristics of KH
- when we plot a graph of equilibrium pressure v/s mole fraction, we get a straight line whose slope is Kh
- Different gases have different values of Kh at the same temperature- Kh is a function of the nature of gas.. The value of Kh differs for a same gas at different temperatures.
-When kH increases with the increase in temperature. The solubility decreases with increase in Kh.
applications of henry’s law: carbonated drinks
To increase the solubility of CO2
in soft drinks and soda water, the
bottle is sealed under high pressure.
applications of henry’s law: bends/ decompression sickness/ caisson disease
Scuba divers must cope with high concentrations of dissolved gases
while breathing air at high pressure underwater. Increased pressure
increases the solubility of atmospheric gases in blood. When the
divers come towards surface, the pressure gradually decreases. This
releases the dissolved gases and leads to the formation of bubbles
of nitrogen in the blood. This blocks capillaries and creates a medical
condition known as bends, which are painful and dangerous to life.
To avoid bends, as well as, the toxic effects of high concentrations
of nitrogen in the blood, the tanks used by scuba divers are filled
with air diluted with helium.
The helium is insoluble in blood. It serves to decrease the amount of dissolved nitrogen and hence reduce its effects.
applications of henry’s law: anoxia/ altitude sickness
At high altitudes the partial pressure of oxygen is less than that at
the ground level. This leads to low concentrations of oxygen in the
blood and tissues of people living at high altitudes or climbers. Low
blood oxygen causes climbers to become weak and unable to think
clearly, symptoms of a condition known as anoxia.
state raoult’s law
the Raoult’s law which states that for a solution of volatile liquids,the partial vapour pressure of each component of the solution
is directly proportional to its mole fraction present in solution.
p1 =p1o x1
where p1o is the vapour pressure of pure component 1 at the same
temperature.
p2 =p2o x2
what is dalton’s partial pressure
According to Dalton’s law of partial pressures, the total pressure
( ptotal ) over the solution phase in the container will be the sum of the
partial pressures of the components of the solution
P total = P1o + (p2o-p1o) x2
Total vapour pressure over the solution can be related to the mole
fraction of any one component.
These
lines (I and II) pass through the points
for which x1
and x2
are equal to unity.
Similarly the plot (line III) of ptotal versus
x2
is also linear (Fig. 2.3). The minimum
value of ptotal is p1
0
and the maximum value
is p2
0
, assuming that component 1 is less
volatile than component 2, i.e., p1
0 < p2
0
.
why is raoul’ts law a special case of henry’s law
If we compare the equations for Raoult’s law and Henry’s law, it
can be seen that the partial pressure of the volatile component or gas
is directly proportional to its mole fraction in solution. Only the
proportionality constant KH differs from p1
0
. Thus, Raoult’s law becomes
a special case of Henry’s law in which KH becomes equal to p1
0
.
what happens when a non volatile solute is added to a volatile solution
In a pure liquid the entire surface is
occupied by the molecules of the liquid. If a
non-volatile solute is added to a solvent to
give a solution [Fig. 2.4.(b)], the vapour
pressure of the solution is solely from the
solvent alone.
This vapour pressure of the
solution at a given temperature is found to
be lower than the vapour pressure of the
pure solvent at the same temperature.
In
the solution, the surface has both solute and
solvent molecules; thereby the fraction of the
surface covered by the solvent molecules gets
reduced. Consequently, the number of
solvent molecules escaping from the surface
is correspondingly reduced, thus, the vapour
pressure is also reduced.
does the decrease in vapour pressure depend upon
The decrease in the vapour pressure of solvent depends on the
quantity of non-volatile solute present in the solution, irrespective of
its nature. For example, decrease in the vapour pressure of water by
adding 1.0 mol of sucrose to one kg of water is nearly similar to that
produced by adding 1.0 mol of urea to the same quantity of water at
the same temperature.
why do we not refer to salt(nacl)? because nacl splits into 2 ions hence there will be twice as many particles,and hence the change will not be similar to urea/glucose which remain as one molecule.
the vapour pressure of the solvent, x1
be
its mole fraction, pi
0
be its vapour pressure
in the pure state. Then according to
Raoult’s law
p1 ∝ x1
and p1
= x1
0
1
p (2.20)
The proportionality constant is equal
to the vapour pressure of pure solvent, 0
1
p .
A plot between the vapour pressure and
the mole fraction of the solvent is linear
