Oxidation and Reduction: Practice Questions

In the following reaction, which substance acts as the reducing agent?

\(Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(l) + 3CO_2(g)\)

What is the oxidation state of sulfur in the thiosulfate ion, \(S_2O_3^{2-}\)?

In the reaction between manganese(IV) oxide and concentrated hydrochloric acid:
\(MnO_2(s) + 4HCl(aq) \rightarrow MnCl_2(aq) + Cl_2(g) + 2H_2O(l)\)
Which of the following descriptions of the electron transfer is correct?

A student bubbles an unknown gas through acidified potassium manganate(VII). The purple solution turns colourless. Which gas is most likely being tested?

When aqueous potassium iodide is added to an unknown solution X, the solution changes from colourless to a reddish-brown color. When solution X is added to acidified potassium manganate(VII), the purple color remains. What can be concluded about solution X?

Explain, in terms of oxidation states, why the displacement reaction \( \text{Fe(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{FeSO}_4\text{(aq)} + \text{Cu(s)} \) is classified as a redox reaction.

When aqueous potassium iodide is added to a solution containing iron(III) ions, a chemical reaction occurs and the mixture turns from yellow to brown. Identify the species that acts as the reducing agent and explain the reaction in terms of electron transfer.

Sulfur dioxide is a common atmospheric pollutant that can act as a reducing agent. In a laboratory investigation, sulfur dioxide gas is bubbled into a test tube containing acidified potassium manganate(VII).

(a) Describe the observation in the test tube and explain the change in terms of the oxidation state of manganese. Show your working for the calculation of the oxidation states of manganese in the reactant and the product.
(b) Construct the ionic half-equation for the reduction of the manganate(VII) ion, \( MnO_4^- \), to the manganese(II) ion, \( Mn^{2+} \), in the presence of hydrogen ions.
(c) In a separate experiment, a piece of iron is coated with a layer of zinc to prevent corrosion. Explain how this method, known as sacrificial protection, works even if the zinc layer is scratched. Use the concept of reactivity and electron transfer in your explanation.
(d) Identify which substance is the oxidizing agent in the following displacement reaction:
\( Zn(s) + Fe^{2+}(aq) \rightarrow Zn^{2+}(aq) + Fe(s) \)