Question

A solution of the primary standard potassium hydrogen phthalate (KHP), KHC8H4O4 , was prepared by dissolving 0.4877 g of KHP in about 50 mL of water. Titration of the KHP solution with a KOH solution of unknown concentration required 28.49 mL to reach a phenolphthalein end point. What is the concentration of the KOH solution?

Answer 1

0.08382 M

Step-by-step explanation:

Step 1: Write the balanced neutralization equation

KHC₈H₄O₄ + KOH ⇒ K₂C₈H₄O₄+ H₂O

Step 2: Calculate the moles corresponding to 0.4877 g of KHC₈H₄O₄

The molar mass of KHC₈H₄O₄ is 204.22 g/mol.

0.4877 g × 1 mol/204.22 g = 2.388 × 10⁻³ mol

Step 3: Calculate the moles of KOH that react with 2.388 × 10⁻³ moles of KHC₈H₄O₄

The molar ratio of KHC₈H₄O₄ to KOH is 1:1. The moles of KOH that react are 1/1 × 2.388 × 10⁻³ mol = 2.388 × 10⁻³ mol.

Step 4: Calculate the molar concentration of KOH

2.388 × 10⁻³ moles of KOH are in 28.49 mL of solution.

2.388 × 10⁻³ mol / 0.02849 L = 0.08382 M