The concentration of Fe²⁺ is given as 0.250 M.
The volume of Fe²⁺ is given as 60.0 ml.
The concentration of Cr₂O₇²⁻ is given as 0.100 M.
The following is the reaction:
Cr₂O₇²⁻ (aq) + 6Fe²⁺ (aq) + 14H⁺ (aq) → 2Cr³⁺ (aq) + 6Fe³⁺ (aq) + 7H₂O (l)
1 mole of Cr₂O₇ reacts with 6 moles of Fe²⁺
The moles of Fe²⁺ present in the solution is:
Moles = Molarity × Volume
= 0.250 M × 60 ml × 1L / 1000 ml
= 0.015 ml
Thus, Fe²⁺ is producing 0.015 mol in the given reaction.
The volume of Cr₂O₇²⁻ required is:
1 mole of Cr₂O₇²⁻ = 6 moles of Fe²⁺
Molarity of Cr₂O₇²⁻ × volume of Cr₂O₇²⁻- = 1/6 moles of Fe²⁺ present in the reaction
Volume of Cr₂O₇²⁻ = 0.015 mol/0.600 mol/L
= 0.025L × 1000ml / 1L
= 25 ml
Hence, the volume of Cr₂O₇²⁻ needed is 25 ml.
