Originally Posted by bc_hawaii
Basically, when C02 levels are high, pH goes down, therefore what is the actual equation between carbon dioxide and carbonic acid?
(I should know this, I have an AP chemistry test new Tuesday...)
Is the equation:
HC03 -> H20 + C02 (threfore, a high concentration of C02 will push the reaction to the left, producing carbonic acid -> lowers pH)
Thanks for the help!
P.S. - I think this water chemistry should help me with my AP chemistry studying, hopefully... Spending a lot of time on these boards rather than with my books...
First, good luck on the AP test. One of my co-workers was chair of the chemistry test committee last year (I am a chemistry professor). There should be plenty of acid-base equilibrium questions on it since we teach so much of that in freshman chemistry!
The above reaction needs to be corrected slightly:
H2CO3(aq) <----> H2O(l) + CO2(aq or g)
The CO2 on the right can be considered aqueous, though it does react quickly to produce the carbonic acid on the left. You are right on the addition of the CO2 producing more carbonic acid. There is more to it though:
H2CO3(aq) <----> HCO3-(aq) + H+(aq)
The carbonic acid is a weak acid which dissociates to bicarbonate (KH buffer!) and hydronium ions (written as the proton above). This is why the pH drops. Also, increasing bicarbonate ions (KH) will then resist the dissociation of carbonic acid, keeping the pH higher (for the same level of dissolved CO2).
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