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# pH watch

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1. i was wondering...if you have the pH of a solution, is it possible to work out the concentration of the substances using kp?
Basically, what i have is the pH changes during the aerobic respiration of yeast.. the pH changes because CO2 is produced and dissociates.. is it possible for me to calculate the amount of CO2 present in the solution? If it's not possible like this..is there any other way i could figure out the amount of CO2 present in the solution using pH?
thanks
2. (Original post by Dal)
i was wondering...if you have the pH of a solution, is it possible to work out the concentration of the substances using kp?
Basically, what i have is the pH changes during the aerobic respiration of yeast.. the pH changes because CO2 is produced and dissociates.. is it possible for me to calculate the amount of CO2 present in the solution? If it's not possible like this..is there any other way i could figure out the amount of CO2 present in the solution using pH?
thanks
Yes, but you'll need to know the concentration of HCO3- ions since it is in the following equilibrium...

CO2 + H20 <=> H2CO3 <=> H+ + HCO3-

pH = 6.1 + log [ (HCO3-) / (0.03 x pCO2) ]
3. any ideas how i could find the H2co3 concentration?
4. (Original post by Dal)
any ideas how i could find the H2co3 concentration?
[H2CO3] = 0.03 x pCO2

that's why I have adjusted the equation the above not to include [H2CO3]so that you don't need to know the concentration of carbonic acid...

other than reading out an equation in my lecture notes i havent got a clue - i am no biochemist - not that they would have a clue about anything... (other than enzymes or the liver... i expect they know everything there is to know about these 'wonderful' things )

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Updated: February 20, 2006
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