Question 12
The amount of iron in a sample of ore can be determined by dichromate titration: Cr₂O₇²⁻ + Fe²⁺ + H⁺ → Cr³⁺ + Fe³⁺ + H₂O A chemist is analyzing a 1.05 g of a sample of ore. She first added it with concentrated H₂SO₄ until all of the ore had dissolved and added enough water carefully to make a 25 mL solution. After some time, all and then added 0.05 g of Zn granulated zinc metal was added to convert all of the Fe³⁺ ions to Fe²⁺: Fe³⁺ (aq) + e⁻ → Fe²⁺ (aq) In parallel, she prepared the dichromate solution by dissolving 2.04 g of K₂Cr₂O₇ in enough water to make 250. mL stock solution. Using a 10 mL pipet, she transferred exactly 10.00 mL of the unknown solution to an Erlenmeyer flask and added 8 drops of sodium diphenylamine sulfonate indicator. Titration was completed upon addition of 32.5 mL of the dichromate solution. What is the % Fe in the ore sample? Note: Use the following molecular weights: K=39, Cr=52, O=16, Fe=56, H=1 Hint: Dichromate is reduced to chromate with 6 electrons
A. 28.9 %
B. 72.2 %
C. 4.8 %
D. 12.0 %
E. 6.0 %
Editorial review: explain the scientific issue and state any assumptions needed for a supported answer.
A. 28.9 %
B. 72.2 %
C. 4.8 %
D. 12.0 %
E. 6.0 %
Editorial review: explain the scientific issue and state any assumptions needed for a supported answer.