Complete Question
You determine that it takes 26.0 mL of base to neutralize a sample of your unknown acid solution. The pH of the solution was 7.82 when exactly 13 mL of base had been added, you notice that the concentration of the unknown acid was 0.1 M. What is the pKa of your unknown acid?
Answer:
The pK_a value is
Explanation:
From the question we are told
The volume of base is
The pH of solution is
The concentration of the acid is
From the pH we can see that the titration is between a strong base and a weak acid
Let assume that the the volume of acid is
Generally the concentration of base
Substituting value
When 13mL of the base is added a buffer is formed
The chemical equation of the reaction is
Now before the reaction the number of mole of base is
Substituting value
Now before the reaction the number of mole of acid is
Substituting value
Now after the reaction the number of moles of base is zero i.e has been used up
this mathematically represented as
The number of moles of acid is
The pH of this reaction can be mathematically represented as
Substituting values