AAMC FL2 C/P #42

[Jony770]

What is the pH of a buffer solution that is 0.2M HCO3- and 2M H2CO3? (First pKa of carbonic acid is 6.37)
Answer: 5.37

If the HH equation is pH= pKa + log([A-]/[HA]) then that should be 6.37+log(0.2/2) which is 4.06 according to wolfram alpha, which is the incorrect. I feel like I'm making a dumb mistake somewhere.

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[aldol16]

You had to have put it into Wolfram Alpha wrong. Also, you need to be able to do simple logs like this without a calculator:

0.2/2 = 1/10 or 0.1 or 10^-1

Therefore,

6.37 + log(10^-1) = 6.37 + -1*log(10) = 6.37 - 1 = 5.37