Problem 70 - Chemistry An Atoms First Approach

Question

One of the classic methods for the determination of the manganese content in steel involves converting all the manganese to the deeply colored permanganate ion and then measuring the absorption of light. The steel is first dissolved in nitric acid, producing the manganese(II) ion and nitrogen dioxide gas. This solution is then reacted with an acidic solution containing periodate ion; the products are the permanganate and iodate ions. Write balanced chemical equations for both of these steps.

Step-by-Step Solution

Answer

Dissolution of steel in nitric acid: \(Mn (s) + 2HNO_3 (aq) \rightarrow Mn^{2+} (aq) + 2NO_2 (g) + H_2O (l) \) Reaction between manganese(II) ion and acidic periodate solution: \( 2Mn^{2+} (aq) + 5IO_4^{-} (aq) + 16H^+ (aq) \rightarrow 2MnO_4^{-} (aq) + 5IO_3^{-} (aq) + 8H_2O (l) \)

Step 1: Identify the reactants and products

In this step, the reactants are steel (assuming pure manganese for simplicity) and nitric acid. The products will be manganese(II) ion and nitrogen dioxide gas. The balanced equation will be: \(Mn (s) + 2HNO_3 (aq) \rightarrow Mn^{2+} (aq) + 2NO_2 (g) + H_2O (l) \) Step 2: Reaction between manganese(II) ion and acidic periodate solution

Step 2: Identify the reactants and products

In this step, the reactants are manganese(II) ion and acidic periodate solution (IO4- ion). The products are permanganate (MnO4-) ion and iodate (IO3-) ion. The balanced equation will be: \( 2Mn^{2+} (aq) + 5IO_4^{-} (aq) + 16H^+ (aq) \rightarrow 2MnO_4^{-} (aq) + 5IO_3^{-} (aq) + 8H_2O (l) \)