Calculate the pH of 0.250 L of a 0.65 M formic acid (HCO2H) - 0.10 M sodium formate (HCO2Na) buffer before (on your own) and after the addition of (a) 0.010 mol of NaOH (on your own) and (b) 0.010 mol of HCl (in the blank). Assume that the volume remains constant.

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To calculate the pH of a buffer solution, you would need to determine the concentration of the acid (HCO2H) and its conjugate base (HCO2Na), as well as the pKa of the acid.

First, let's calculate the initial pH of the buffer before any addition of NaOH or HCl.

The Henderson-Hasselbalch equation is used to determine the pH of a buffer solution and is given as:

pH = pKa + log ([conjugate base]/[acid])

The pKa of formic acid (HCO2H) is 3.75.

Now, let's calculate the concentration of HCO2H and HCO2Na in the buffer solution before any addition:

HCO2H concentration = 0.65 M (given)
HCO2Na concentration = 0.10 M (given)

Substituting these values into the Henderson-Hasselbalch equation:

pH = 3.75 + log (0.10/0.65)

Simplifying further:

pH = 3.75 + log (0.1538)

Using a calculator, you can calculate the logarithm and obtain the pH value.

Now, let's move on to the effect of adding NaOH and HCl to the buffer solution.

(a) Addition of 0.010 mol of NaOH:
When NaOH is added to the buffer solution, it reacts with formic acid (HCO2H) to form sodium formate (HCO2Na) and water (H2O). This reaction reduces the concentration of formic acid and increases the concentration of sodium formate in the buffer.

To determine the resulting pH, you would need to calculate the new concentrations of HCO2H and HCO2Na in the buffer solution. The total volume remains constant at 0.250 L.

New HCO2H concentration = initial HCO2H concentration - mol NaOH
New HCO2H concentration = 0.65 M - 0.010 mol / 0.250 L

New HCO2Na concentration = initial HCO2Na concentration + mol NaOH
New HCO2Na concentration = 0.10 M + 0.010 mol / 0.250 L

After obtaining the new concentrations, you can use the Henderson-Hasselbalch equation as before to calculate the new pH.

(b) Addition of 0.010 mol of HCl:
When HCl is added to the buffer solution, it reacts with sodium formate (HCO2Na) to form formic acid (HCO2H) and sodium chloride (NaCl). This reaction reduces the concentration of sodium formate and increases the concentration of formic acid in the buffer.

To determine the resulting pH, you would need to calculate the new concentrations of HCO2H and HCO2Na in the buffer solution. The total volume remains constant at 0.250 L.

New HCO2H concentration = initial HCO2H concentration + mol HCl
New HCO2H concentration = 0.65 M + 0.010 mol / 0.250 L

New HCO2Na concentration = initial HCO2Na concentration - mol HCl
New HCO2Na concentration = 0.10 M - 0.010 mol / 0.250 L

After obtaining the new concentrations, you can use the Henderson-Hasselbalch equation as before to calculate the new pH.

Remember to substitute the new concentrations into the equation and perform the calculations using a calculator to obtain the final pH values.