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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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Nyjt400ex Nyjt400ex
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11 years ago
There are many organic acids and bases in our cells and their presence modifies the ph of fluids inside them. One of these is lactic acid, CH3CHOHCOOH. A solution of equal concentrations of lactic acid and sodium lactate has a ph = 3.08 Using these values determine the pKa and Ka values of lactic acid..
What would the Ph be if the acid had twice the concentration of the salt sodium lactate?
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#1
11 years ago
The relationship between pKa and pH is:

pH = pKa + log [HA]/[A-]

With the concentration equal, the pKa is just the pH of the system.

pKa = 3.08

Ka = 10^-3.08 = 8.31E-4



[EDIT]:

If the acid was twice the concentration of the sodium salt, then [HA] = 2x, [A-] = x.

pH = pKa + log [HA]/[A-]

pKa = pH - log [HA]/[A-]

pKa = 3.08 - log [2x/1x]

pKa = 3.08 - log[2]

pH = 3.08 - .301

pH = 2.78
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