3. Formic acid, HCHO2, has a Ka = 1.8 x 10-4. We are asked to prepare a buffer solution having a pH of 3.40 from a 0.10 M HCHO2 (formic acid solution) and 0.10 M NaCHO2 (sodium formate; formate ion is the conjugate base). How many mL of the NaHCO2 solution should be added to 20.0 mL of the 0.10 M HCHO2 solution to make the buffer? 4. When 5 drops of 0.10 M NaOH were added to 20 mL of the buffer in problem 3, the pH went from 3.40 to 3.43. Write a net ionic equation to explain why the pH didnât go up to about 10, as it would have if that amount of NaOH were added to distilled water or to about 20.0 mL of 0.00040 M HCl, which also would have a pH of 3.40.

Question

3. Formic acid, HCHO2, has a Ka = 1.8 x 10-4. We are asked to prepare a buffer solution having a pH of 3.40 from a 0.10 M HCHO2 (formic acid solution) and 0.10 M NaCHO2 (sodium formate; formate ion is the conjugate base). How many mL of the NaHCO2 solution should be added to 20.0 mL of the 0.10 M HCHO2 solution to make the buffer? 4. When 5 drops of 0.10 M NaOH were added to 20 mL of the buffer in problem 3, the pH went from 3.40 to 3.43. Write a net ionic equation to explain why the pH didnât go up to about 10, as it would have if that amount of NaOH were added to distilled water or to about 20.0 mL of 0.00040 M HCl, which also would have a pH of 3.40.

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