Question

Balance the following redox equation, identifying the element oxidized and the element reduced. Show all work to solve the problem.
Cr2O7 2- + C2H5OH --> Cr3 + CO2

Answer 1

Explanation:

A redox equation is defined as an equation that shows reduction and oxidation are taking place simultaneously in a chemical reaction.

When electrons are lost in a chemical reaction then it is known as oxidation reaction. Whereas when electrons are gained in a chemical reaction then it is known as a redox reaction.

For example, $Cr_{2}O^{2-}_{7} + C_{2}H_{5}OH \rightarrow Cr^{3+} + CO_{2}$

Reduction-half reaction: $Cr_{2}O^{2-}_{7} + 3e^{-1} \rightarrow Cr^{3+}$

Oxidation state of Cr in $Cr_{2}O^{2-}_{7}$ is +6.

Oxidation-half reaction: $C_{2}H_{5}OH \rightarrow CO_{2} + 6e^{-1}$

Oxidation state of C in $C_{2}H_{5}OH$ is -2 and in $CO_{2}$ oxidation state of C is +4.

Now, to balance the equation multiply reduction-half reaction by 2.

$2Cr_{2}O^{2-}_{7} + 6e^{-1} \rightarrow 2Cr^{3+}$

Thus, the combined balanced chemical reaction equation will be as follows.

          $2Cr_{2}O^{2-}_{7} + C_{2}H_{5}OH \rightarrow 2Cr^{3+} + CO_{2}$

Answer 2

Oxygen, a chalcogen, has oxidation state 2-. Therefore, Cr is Cr2O7^2- has a charge of 6+. This charge becomes 0 after the reaction, so Cr gained electrons and was reduced. This also means that Cr2O7 was the oxidizing agent.

Meanwhile, since H has a charge of 1+, the oxidation state of C in C2H5OH is 2-. In the product CO2, its charge is 4+. This means that it lost electrons, and was oxidized. Therefore, ethanol (C2H5OH) is the reducing agent.