Answer to Question #271106 in Chemistry for khryst

Question

A solution of HClO4 was standardized by dissolving 0.4008 g of primary-standard-grade HgO in a solution of KBr:

HgO(s) + 4Br- + H2O  HgBr42- + 2OH-

The liberated OH- consumed 43.75 mL of the acid. Calculate the molar concentration of the HClO4.

Answer 1

Solution:

Calculate the moles of HgO:

The molar mass of HgO is 216.59 g/mol

Hence,

(0.4008 g HgO) × (1 mol HgO / 216.59 g HgO) = 0.00185 mol HgO

Balanced chemical equations:

(1): HgO + 4Br⁻ + H₂O → HgBr₄²⁻ + 2OH⁻ 

(2): OH⁻ + HClO₄ → ClO₄⁻ + H₂O

According to the chemical equation (1): 1 mol HgO produces 2 mol OH⁻

Thus, 0.00185 mol HgO produces:

(0.00185 mol HgO) × (2 mol OH⁻ / 1 mol HgO) = 0.0037 mol OH⁻

According to the chemical equation (2): 1 mol OH⁻ reacts with 1 mol HClO₄

Thus, 0.0037 mol OH⁻ reacts with:

(0.0037 mol OH⁻) × (1 mol HClO₄ / 1 mol OH⁻) = 0.0037 mol HClO₄

Molarity of HClO₄ = Moles of HClO₄ / Volume of HClO₄

Molarity of HClO₄ = (0.0037 mol) / (0.04375 L) = 0.08457 M = 0.0846 M

Molarity of HClO₄ = 0.0846 M

Answer: The molar concentration of HClO₄ is 0.0846 M