Consider the unbalanced redox reaction: Cr_2O_2^-7(aq)+Cu(s)-->Cr^3+(aq)+Cu^2+(aq) PART A: ...


Consider the unbalanced redox reaction:



Balance the equation.

Express your answer as a chemical equation. Identify all of the phases in your answer.


Determine the volume of a 0.575 M K_2Cr_2O_7 solution required to completely react with 5.64 g of Cu. Express your answer using three significant figures.

Redox Reaction:

A redox reaction involves electron transfer between two species. The species that loses/gains electrons is oxidized/reduced respectively. Each of these processes can be written as a balanced half-reaction showing the electron loss or gain. When summed together the net redox reaction must be balanced in mass and charge with no electrons present.

Answer and Explanation: 1

Question a)

  • Copper is oxidized here from zero in the metal to +2 in the aqueous ion.
  • Oxidation half-reaction: {eq}3Cu (s) \rightarrow 3Cu^{2+} (aq) + 6e^- {/eq}
  • Chromium is reduced here from +6 in dichromate anion to +3 in the aqueous ion.
  • Reduction half-reaction: {eq}14H^+ (aq) + Cr_2O_7^{2-} (aq) + 6e^- \rightarrow 2Cr^{3+} (aq) + 7H_2O (l) {/eq}
  • Net reaction: {eq}3Cu (s) + 14H^+ (aq) + Cr_2O_7^{2-} (aq) \rightarrow 3Cu^{2+} (aq) + 2Cr^{3+} (aq) + 7H_2O (l) {/eq}

Question b)

  • moles of copper = {eq}5.64 g \times \dfrac{1mol}{63.546 g} = 0.0888 mol {/eq}

For equivalence this requires (1/3)(0.0888) = 0.0296 mol of potassium dichromate solution.

  • volume of potassium dichromate solution required = {eq}\dfrac{n}{C} = \dfrac{0.0296 mol}{0.575 M} = 0.0515 L = 51.5 mL {/eq}

Learn more about this topic:

Balancing Redox Reactions and Identifying Oxidizing and Reducing Agents


Chapter 10 / Lesson 13

Learn about oxidizing and reducing agents, how to find them, and how to identify them in redox reactions. Learn about the different types of redox reactions and how to identify a redox reaction.

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