Question

A student is asked to standardize a solution of barium hydroxide. He weighs out 0.925 g potassium hydrogen phthalate (KHC8H4O4, treat this as a monoprotic acid). It requires 28.5 mL of barium hydroxide to reach the endpoint.

A. What is the molarity of the barium hydroxide solution? This barium hydroxide solution is then used to titrate an unknown solution of perchloric acid.

B. If 26.0 mL of the barium hydroxide solution is required to neutralize 26.9 mL of perchloric acid, what is the molarity of the perchloric acid solution?

Answer 1

• potassium hydrogen phthalate molecular wieght is 204.22 g/mol
• no. of moles of potassium hydrogen phthalate is 0.925/204.22 = 0.00453 moles
• 2 moles of potassium hydrogen phthalate requires 1 mole of barium hydroxide (since it is diacidic base).
• i.e., 0.00225 moles of barium hydroxide requires to nutralise 0.925 g of potassium hydrogen phthalate
• molarity of Ba(OH)₂ is 0.00225/0.0285 = 0.079 M
• for neutralization formula is M₁V₁/N_{1 =}M₂V₂/N₂
• M₁ = 0.079 m, V₁ =26 mL, N₁ = 2,  V₂ = 26.9, N₂ = 1, M₂ = ?
• (0.079 X 26)/2 = (M₂ X 26.9)/1
• 1.027 = M₂ X 26.9
• M₂ = 1.027/26.9 = 0.038 M
• molarity of perchloric acid is 0.038