Question

A 0.7834 g sample of a primary standard KHP was titrated with 38.45 mL of NaOH solution to a phenolphthalein end-point. What is the molarity of the NaOH solution?

Answer 1

0.0998 M

Step-by-step explanation:

KHP is a weak monoprotic acid. This means that the moles of acid are equal to the moles of OH⁻ that were added in the titration.

KHP Molecular weight = 204.22 g/mol

• moles KHP = 0.7834 g ÷ 204.22 g/mol = 3.836x10⁻³ mol KHP

So 3.836x10⁻³ moles of OH⁻ were added in the titration. With moles and volume we can calculate the molarity of the NaOH solution:

38.45 mL ⇒ 38.45/1000 = 0.03845 L

• 3.836x10⁻³ mol OH⁻ / 0.03845 L = 0.0998 M