Posted by Marcus on .
The question is: what is the ratio [NH3/[NH4+] in an ammonia/ammonium chloride buffer solution with pH= 10.00? (pKa for ammonia=9.25)
When working the problem, I tried to solve it a bit backwards, in that I plugged in each of the multiple choices I was given to see which would equal 10.
Such as:
pH=pKa +log(salt/base)
9.25 +log(5.62)=10 pH
So my ratio would be 5.62 since that number makes it equal 10, or am I just doing this completely wrong?

Chemistry 
DrBob222,
My calculator is broken so I can't check your number; however, there is nothing wrong with doing it the way you tried. You can do it straight, however, by
pH = pKa + log (base)/(acid)
10 = 9.25 + log (base)/(acid) and solve for (base)/(acid)