Titration: Molarity of Acid or Base

Question

An aqueous solution of potassium hydroxide is standardized by titration with a 0.196 M solution of hydrochloric acid.

If 21.9 mL of base are required to neutralize 25.0 mL of the acid, what is the molarity of the potassium hydroxide solution?

______M potassium hydroxide

Answer 1

KOH + HCl ==> KCl + H2O ... balanced equation

moles HCl = 25.0 ml x 1 L/1000 ml x 0.196 moles/L = 0.0049 moles HCl

moles KOH needed = 0.0049 moles KOH (1:1 mole ratio in the balanced equation)

Since volume KOH used = 25.0 ml, this is equivalent to 0.025 L, we have...

Molarity of KOH) = 0.0049 moles/0.025 L = 0.196 M

We could have seen this from the start since both reactants are present in equal volumes so molarity must be equal.