Question

Determine the concentration of a solution of sodium hydroxide (NaOH) using a 0.500M Potassium Hydrogen Phthalate (KHP) standard solution. Acid-base indicator phenolphthalein is added in its (colorless) acidic form to a precise volume sample of KHP. The base NaOH is slowly added to the same of KHP. Once all the KHP has reacted with the base, the first excess drop of NaOH will cause the indicator to convert to its basic (pink) form.

Answer 1

Answer:

0.425M NaOH assuming the volume of KHP was 25.50mL and the volume of the NaOH solution was 30.0mL

Explanation:

The KHP reacts with NaOH as follows:

KHP + NaOH → KNaP + H₂O

Where 1 mole of KHP reacts per mole of KNaP

That means, the moles of KHP added to the NaOH solution = Moles NaOH at equivalence point. With the moles of NaOH and the volume in liters we can find the molar concentration of NaOH.

Assuming the volume added of KHP was 25.50mL and the solution of NaOH contains 30.0mL (0.0300L), the concentration of the NaOH is:

Moles KHP = Moles NaOH:

25.50mL = 0.02550L * (0.500mol / L) = 0.01275 moles KHP = Moles NaOH

Molarity NaOH:

0.01275 moles NaOH / 0.0300L =

0.425M NaOH assuming the volume of KHP was 25.50mL and the volume of the NaOH solution was 30.0mL