[BreakingBad20]

Equation: CO₂ + H₂O  H₂CO₃

K_h = [H₂CO₃] / [CO₂] = 0.0017 @25°C

Example point: pH = 4.4 @ t = 0

[H₂CO₃] = 10^-(4.4) = 3.98107*10^(-05)

[CO₂] = 10^-(4.4) / 0.0017 = 0.023418069

Is this correct?

[Borek]

You have posted some random numbers and random operations and you expect us to miraculously guess what you mean?

But the short answer is: it is wrong. No matter what you are doing, this line:

Example point: pH = 4.4 @ t = 0

[H₂CO₃] = 10^-(4.4) = 3.98107*10^(-05)

makes no sense. Concentration of a weak acid is not equal to concentration of H⁺.

[dayglo]

Henderson-Hasselbach equation? Try that.

[BreakingBad20]

I haven't done chemistry in a while, it's been more chemical engineering than anything else and then all of a sudden we have been getting more chemistry based experiments. Someone had explained that this was the way to do it but I wasn't sure so that's why I posted it. Sorry for the lack of information.
Basically, the experiment is to calculate the rate of absorption of carbon dioxide into water from analysis of liquid solutions flowing down an absorption column. Water is pumped down through the absorption column and carbon dioxide is pumped from the bottom and goes up through the absorption column. The water that is pumped down through the column is collected in a tank that pumps the water back up and into the absorption column. While this is happening a data logger with a probe in the tank is constantly measuring the pH of the water being circulated. The pH is recorded every 30 seconds, hence where I got pH = 4.4 @ t = 0. I need to convert these values of pH using the equation and K_h in the original post.

I'm trying to locate my old textbook where I have notes on this because the general chemistry books in the library are just confusing me. Can you give any tips on how to do this?

[Borek]

Simplest approach that I can think about is to treat carbonic acid as a weak monoprotic acid (it is diprotic, but the second dissociation step is so weak it can be safely ignored here). You will need an equation that combines [H⁺], Ca (acid concentration) and Ka - just solve it for Ca.

See if this page: http://www.chembuddy.com/?left=pH-calculation&right=pH-weak-acid-base doesn't help.