Answer:
0.0146 M
Explanation:
The relevant chemical reaction equation is as follows:
Cr₂O₇²⁻ + 6Fe²⁺ + 14H⁺ ⇒ 2Cr³⁺ +6Fe³⁺ + 7H₂O
In order to find the concentration of Cr₂O₇²⁻, the number of moles of Cr₂O₇²⁻ in the solution must be found. This can be found by relating it to the number of moles of the analyte (Fe²⁺), which can be calculated as follows:
(35.0 mL)(0.250mol/L) = 8.75 mmol Fe²⁺
This is the amount of Fe²⁺ required to react with all of the Cr₂O₇²⁻ present.The moles of Fe²⁺ and Cr₂O₇²⁻ in the reaction are related as follows:
8.75 mmol Fe²⁺ x (Cr₂O₇²⁻ / 6Fe²⁺) = 1.4583...mmol Cr₂O₇²⁻
The concentration of the Cr₂O₇²⁻ solution is then calculated as follows:
(1.4583...mmol) / 100mL = 0.146 mol/L = 0.146 M
