Question

Consider the following unbalanced redox reaction.
Cr2O2−7(aq)+Cu(s)→Cr3+(aq)+Cu2+(aq)

Part A

Balance the equation:
αCr2O2−7(aq)+βH+(aq)+γCu(s)→δCr3+(aq)+ϵH2O(l)+κCu2+(aq)

Give your answer as an ordered set of numbers α, β, γ, ... Use the least possible integers for the coefficients.

Part B

Determine the volume of a 0.950 M K2Cr2O7 solution required to completely react with 5.15 g of Cu.

Answer 1

PART-A:

αCr₂O₇⁻²_(aq)+βH+_(aq)+γCu_(s) δCr³⁺_(aq)+ϵH₂O_(l)+κCu²⁺_(aq)

Cr₂O₇⁻²_(aq)+ 14H+_(aq)+ Cu_(s)​ 2Cr³⁺_(aq) + 7H₂O_(l) + Cu²⁺_(aq)

α = 1, β = 14, γ = 1, δ = 2, ϵ = 7, κ = 1

PART-B:

Cr₂O₇⁻²_(aq)+ 14H+_(aq)+ Cu_(s)​ 2Cr³⁺_(aq) + 7H₂O_(l) + Cu²⁺_(aq)

1 mol 63.54 (Cu molar mass = 63.54).

? 5.15 g

= 5.15 x 1/63.54

= 0.0810 moles.

According to the question K2Cr2O7 concentration = 0.950 M

Molarity = moles/Volume in litres

0.950 = 0.0810 / V

V = 0.0810 / 0.950

V = 0.08531 L

V = 85.317 mL.