Answer to Question #256769 in Chemistry for Syu

Question

In an experiment of titration, 25.0 mL of potassium hydroxide solution is poured

into a conical flask. A few drops of phenolphthalein are added into the solution.

The solution in the conical flask is titrated with 1.0 M sulphuric acid.

a)What is the function of phenolphthalein in this experiment

b)Write a balanced chemical equation for the reaction.

c) In this experiment, 20.00 mL sulphuric acid needed to react with 25.0 

mL of potassium hydroxide.

i. Calculate the mole for sulphuric acid.

ii. Calculate the molarity of potassium hydroxide solution.

Answer 1

a) Phenolphthalein is the indicator helping to identify the equivalence point of the titration.

b) 2KOH + H₂SO₄ = K₂SO₄ + 2H₂O

c)

i) According to this equation, n (KOH) = 2 x n (H₂SO₄)

C_M = n / V

n = C_M x V

n (H₂SO₄) = 1.0 x 0.020 = 0.020 mol

ii) n (KOH) = 2 x n (H₂SO₄) = 2 x 0.020 = 0.04 mol

C_M (KOH) = 0.04 / 0.025 = 1.6 M