[LHM]

1. 25.0 cm³ of a 0.050 M solution of formic acid, HCOOH, was neutralized with 25.0 cm³ of a 0.050 M solution of sodium hydroxide, NaOH. What is the pH of the resulting solution? K_a for HCOOH=2.1*10^-4.
A) 5.96
B) 6.61
C) 7.39
D) 8.04

The answer is D, but when I try to do this, I can't get D. When I first set it up using the reaction stoichiometry to find the amount of excess acid so that I can then set up the equilibrium table, I get that there are 0.00125 moles of acid and 0.00125 moles of base, so that they completely react to form salt and water. But then, there isn't any excess acid left to set up an equilibrium table, so how am I supposed to do this?

2. When titrating a weak acid with a strong base, which of the following indicators would be best to use?

A) quinaldine red, pK_a=2.75
B) bromeresol green, pK_a=7.10
C) cresol purple, pK_a=8.32
D) not enough information is provided

Since it never really specified which acid or base, how do you know that the answer is C?

[Borek]

http://www.titrations.info/acid-base-titration-equivalence-point-calculation