Question

One of the classic methods for determining 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 the periodate ion; the products are the permanganate and iodate ions. Write balanced chemical equations for both of these steps.

Short answer

The balanced chemical equations for the consecutive steps to determine the manganese content in steel are: 1. \(Mn (s) + 2 HNO_3 (aq) \rightarrow Mn^{2+} (aq) + 2 NO_2 (g) + H_2O (l)\) 2. \(2 Mn^{2+} (aq) + 5 IO_4^- (aq) + 12 H^+ (aq) \rightarrow 2 MnO_4^- (aq) + 5 IO_3^- (aq) + 6 H_2O (l)\)

Step-by-step solution

Dissolution of steel in nitric acid to produce manganese(II) ions and nitrogen dioxide gas

To write a balanced chemical equation for the dissolution of steel in nitric acid, we first need to identify the component of steel that contains manganese. Steel is an alloy mainly composed of iron and carbon, but it also contains trace amounts of manganese. The manganese content in steel is represented by Mn. The dissolution of steel in nitric acid (HNO₃) will produce manganese(II) ions (Mn²⁺) and nitrogen dioxide gas (NO₂). The initial chemical equation can be written as: Mn (s) + HNO₃ (aq) → Mn²⁺ (aq) + NO₂ (g) Now we need to balance the chemical equation. The reaction also produces H₂O (l) as a byproduct. The balanced chemical equation is: Mn (s) + 2 HNO₃ (aq) → Mn²⁺ (aq) + 2 NO₂ (g) + H₂O (l)

Reaction of manganese(II) ions solution with acidic periodate ion solution to produce permanganate and iodate ions

We now need to write a balanced chemical equation for the reaction of the solution containing manganese(II) ions (Mn²⁺) with an acidic solution containing the periodate ion (IO₄⁻). The products of this reaction are permanganate ions (MnO₄⁻) and iodate ions (IO₃⁻). The initial chemical equation can be written as: Mn²⁺ (aq) + IO₄⁻ (aq) → MnO₄⁻ (aq) + IO₃⁻ (aq) Now we need to balance the charges and the atoms in the equation. The balanced chemical equation for the reaction is: 2 Mn²⁺ (aq) + 5 IO₄⁻ (aq) + 12 H⁺ (aq) → 2 MnO₄⁻ (aq) + 5 IO₃⁻ (aq) + 6 H₂O (l) Both balanced chemical equations for the consecutive steps to determine the manganese content in steel are provided as follows: 1. Mn (s) + 2 HNO₃ (aq) → Mn²⁺ (aq) + 2 NO₂ (g) + H₂O (l) 2. 2 Mn²⁺ (aq) + 5 IO₄⁻ (aq) + 12 H⁺ (aq) → 2 MnO₄⁻ (aq) + 5 IO₃⁻ (aq) + 6 H₂O (l)

Key concepts

Manganese Content Analysis

When analyzing the manganese content in steel, one must convert manganese into a detectable form. This involves a chemical transformation to the permanganate ion, which has a distinct and deep color. The intensity of this color can be measured to determine the concentration of manganese, leveraging tools like spectrophotometry. This process provides a precise way to quantify manganese levels, crucial for ensuring material quality and performance.

Key steps in manganese content analysis include:

• Dissolving the steel sample to release manganese into a solution.
• Reacting manganese to form the permanganate ion for easy measurement.

These steps must be accurate for effective analysis. Thus, understanding the chemical transformations involved is vital.

Steel Dissolution

The dissolution of steel is the initial step in analyzing its chemical composition. Steel is primarily made up of iron, but it also contains other important elements like carbon and manganese. To analyze these elements, the steel must be broken down chemically.

In the manganese analysis process, the steel sample is dissolved in nitric acid. This process transforms manganese present in steel into manganese(II) ions by reacting with nitric acid, a strong oxidizing agent. During this reaction:

• Manganese is oxidized and dissolved as manganese(II) ions ( Mn^{2+} ).
• Nitric acid produces nitrogen dioxide gas ( NO_2 ) as a byproduct.
• Water ( H_2O ) is also generated.

The balanced chemical equation for this transformation is:
Mn (s) + 2 HNO_3 (aq) → Mn^{2+} (aq) + 2 NO_2 (g) + H_2O (l)

This equation shows how stoichiometry ensures that all atoms are accounted for and conserved in the reaction, vital for accurate analytical assessments.

Balanced Chemical Equations

Chemical equations represent the substances involved and the changes they undergo in a reaction. A balanced chemical equation ensures the number of each type of atom is equal on both sides of the equation, reflecting the law of conservation of mass.

In analyzing manganese content, balancing equations is fundamental. In the first step, when manganese in steel reacts with nitric acid, it's crucial to balance the manganese and nitrogen atoms to ensure accuracy. Similarly, in the next step, when manganese(II) ions react with periodate ions, balancing not only atoms but also charges involved in the ionic species is necessary:

• The manganate reaction with periodate is a complicated redox reaction.
• This requires careful balancing of charges between manganese(II), permanganate, and iodate ions.

The balanced equation for the manganate reaction is:
2 Mn^{2+} (aq) + 5 IO_4^- (aq) + 12 H^+ (aq) → 2 MnO_4^- (aq) + 5 IO_3^- (aq) + 6 H_2O (l)

Balancing these chemical equations ensures precision in calculating quantities, which is critical for accurate manganese content analysis.