Practice Reduction in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The gain of electrons by an atom, ion, or molecule during a chemical reaction, resulting in a decrease in its oxidation state.

Grabbing electrons. The charge gets 'reduced' (becomes more negative).

Showing a random 20 of 50 problems.

Example 1

medium
Write the reduction half-reaction for Ag+\text{Ag}^+ forming silver metal.

Example 2

easy
Is reduction always accompanied by oxidation in a chemical reaction?

Example 3

easy
In Cu2++2e−→Cu\text{Cu}^{2+}+2e^-\rightarrow\text{Cu}, is copper oxidized or reduced?

Example 4

easy
In a galvanic cell, reduction occurs at the ____ electrode.

Example 5

easy
In Br2+2e−→2Br−\text{Br}_2 + 2e^- \rightarrow 2\text{Br}^-, what is the change in oxidation number of Br?

Example 6

medium
Identify the species reduced in Fe2O3+3CO→2Fe+3CO2\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2.

Example 7

medium
In the electrolysis of molten NaCl, what is reduced at the cathode?

Example 8

medium
In Cu2++2e−→Cu\text{Cu}^{2+}+2e^-\rightarrow\text{Cu}, how many electrons are gained per copper, and what is the oxidation-state change?

Example 9

medium
In Zn+Cu2+→Zn2++Cu\text{Zn}+\text{Cu}^{2+}\rightarrow\text{Zn}^{2+}+\text{Cu}, which species is reduced and is it the oxidizing agent?

Example 10

medium
Hydrogen in H2\text{H}_2 (state 0) becomes hydride H−\text{H}^- in NaH\text{NaH}. Is hydrogen reduced? By how many electrons per atom?

Example 11

hard
In Cr2O72−→2Cr3+\text{Cr}_2\text{O}_7^{2-} \rightarrow 2\text{Cr}^{3+}, how many moles of electrons are needed per mole of dichromate?

Example 12

easy
OIL RIG: what does 'RIG' stand for?

Example 13

easy
When Fe3+\text{Fe}^{3+} becomes Fe2+\text{Fe}^{2+}, is iron oxidized or reduced?

Example 14

hard
In a daniell cell with overall Zn+Cu2+→Zn2++Cu\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}, write the half-reaction at the cathode.

Example 15

easy
In 2Na+Cl2→2NaCl2\text{Na}+\text{Cl}_2\rightarrow2\text{NaCl}, which element is reduced?

Example 16

medium
In MnO4−→Mn2+\text{MnO}_4^-\rightarrow\text{Mn}^{2+}, Mn goes from +7+7 to +2+2. How many electrons are gained, and is this reduction?

Example 17

medium
In 2Mg+O2→2MgO2\text{Mg}+\text{O}_2\rightarrow2\text{MgO}, write oxygen's reduction half-reaction.

Example 18

medium
Why is the reduced species called the oxidizing agent rather than the reducing agent?

Example 19

medium
Write the reduction half-reaction for nitrate to NO in acidic solution: NO3−→NO\text{NO}_3^- \rightarrow \text{NO}.

Example 20

medium
In Cl2+2NaBr→2NaCl+Br2\text{Cl}_2 + 2\text{NaBr} \rightarrow 2\text{NaCl} + \text{Br}_2, which element is reduced?
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