Question

The pH = pKa at equivalence point

a) at half the volume of base needed to reach equivalence point

b) when all of the acid is neutralized

c) plus or minus one pH unit from equivalence

d) none of the above

Please also EXPLAIN your asnwer!

Answer 1

Answer is

a) at half the volume of base needed to reach equivalence point

At the half equivalence point, say we have 10 moles of Weak acid (WA), so there will be 5 moles of Strong base (SB) as ("half equivalence").

So we know that the 10 moles will be neutralized to 5 moles of WA by the SB. If we do this then the conjugate base is also now equal to the Weak acid since it will increase by 5 moles.

Weak Acid = Conjugate base

pH = pKa + log 1

pH = pKa

It requires half of the volume of base reached needed to reach equivalence point.