The equivalent point in a titration of `40.0mL` of a sodium of a weak monoprotic acid occurs when `35.0mL` of a `0.10M NaOH` solutio has been added. The `pH` of the solution is 5.5 after the addition of `20.0mL` of `NaOH` solution. What is the dissociation constant of the acid ?

Explanation

To find the dissociation constant (Ka) of the weak monoprotic acid (HA) from the given titration data, we can follow these steps:

### Step 1: Determine the moles of NaOH at the equivalence point
Given that the equivalence point occurs when 35.0 mL of 0.10 M NaOH has been added, we can calculate the moles of NaOH used:

\[ \text{Moles of NaOH} = \text{Volume (L)} \times \text{Concentration (M)} = 0.035 \, \text{L} \times 0.10 \, \text{mol/L} = 0.0035 \, \text{mol} \]
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