Chapter 16 – Problem 7
Sparkling Drinks
CO2 in H2O has Henry’s law constant kh = 1.25e6 mmHg. What mole fraction of CO2 in
water will lead to “bubbling up” and a vapor pressure equal to 1 atm?
This problem is gone in like 10 seconds or as quick as you can punch it into your
calculator. We have a nice equation that relates the mole fraction of a solute, which in
this case is CO2, in a solvent, which is water to the vapor pressure of a liquid. It is shown
below.
p CO2   CO2 * k h
We know the Henry’s law constant, kh, since it was given to us. The pressure is simply
the vapor pressure given. We can assume this because at room temperature the vapor
pressure of pure water is 0.0231 atm, which contributes practically nothing to the total
vapor pressure of 1 atm.
**FYI – In general chemistry we did an experiment and collected CO2. We assumed that
the gas collected was completely CO2 even though some water vapor was present. This
assumption was valid though because the contribution of the water vapor pressure is
negligible compared to CO2’s vapor pressure.**
So doing some hard algebra and plugging in our values given we arrive at the following
answer.
 CO 
2
p CO2
kh

760 mmHg
 6.08e  4
1.25e6 mmHg