Chemistry - Redox Reactions Question with Solution | TestHub
A forensic chemist needed to determine the concentration of HCN in the blood of a suspected homicide victim and decided to titrate a dilute sample of the blood with iodine using the reaction: HCN(aq) + I₃⁻(aq) ICN(aq) + 2I⁻(aq) + H⁺(aq). A diluted blood sample of volume 15.0 ml was titrated to the stoichiometric point with 5.0 ml of an I₃⁻ solution. The molar concentration of the I₃⁻ solution was determined by titrating it against arsenic (III) oxide, As₄O₆, which in solution forms arsenious acid, H₃AsO₃. A volume of 10.0 ml of the triiodide solution was needed to reach the stoichiometric point on a 0.1188 g sample of As₄O₆ in the reaction: H₃AsO₃(aq) + I₃⁻(aq) + H₂O(l) H₃AsO₄(aq) + 3I⁻(aq) + 2H⁺(aq). (Atomic mass of As = 75)
What is the molar concentration of the triiodide solution?
Options:
Answer:
Solution:
M(As₄O₆) = 4 × 75 + 96 = 396, so 0.1188 g = 0.3 mmol, giving 4 × 0.3 = 1.2 mmol H₃AsO₃. Since H₃AsO₃ : I₃⁻ = 1 : 1, I₃⁻ = 1.2 mmol in 10.0 ml. Molarity = 1.2/10 = 0.12 M, matching (b).
