Ka for General Chemistry

Question

The Ka for formic acid (HCHO2) is 1.8 x 10^-4. What is the pH for a 0.35 aqueous solution of sodium formate (NaCHO2)?

Answer 1

Nick, to answer your question in your "Asker's Comment"  about choosing which "x" after the quadratic, yes you are right  : .... u choose the (0.25243) because you cannot have a neg atm.

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CHO2-  in water --> HCHO2 & OH-

Kb = Kwater / Ka = 1e-14 / 1.8e-4 = 5.56e-11

Kb = [HCHO2] [OH-] / [CHO2-]

5.56e-11 = [x] [x] / [0.35]

x2 = 1.9e-11

x = [OH-] = 4.4e-6

pOH = 5.36

pH = 14 -pOH

your answer : 8.64