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 HCN in the blood sample?
Options:
Answer:
Solution:
HCN : I₃⁻ = 1 : 1, so HCN = 5.0 ml × 0.12 M = 0.6 mmol in 15.0 ml of blood. Molarity = 0.6/15 = 0.04 M, matching (a).
