Question

Write balanced chemical equations for each of the following reactions characteristic of elemental manganese: (a) It reacts with aqueous \(\mathrm{HNO}_{3}\) to form a solution of manganese(II) nitrate. (b) When solid manganese(II) nitrate is heated to \(450 \mathrm{~K}\), it decomposes to \(\mathrm{MnO}_{2}\). (c) When \(\mathrm{MnO}_{2}\) is heated to \(700 \mathrm{~K}\), it decomposes to \(\mathrm{Mn}_{3} \mathrm{O}_{4}\). (d) When solid \(\mathrm{MnCl}_{2}\) is reacted with \(\mathrm{F}_{2}(g)\), it forms \(\mathrm{MnF}_{3}\) (one of the products is \(\mathrm{ClF}_{3}\) )

Short answer

Short Answer: Reaction (a): \( 2 \mathrm{Mn}(s) + 8 \mathrm{HNO}_3(aq) \rightarrow 2 \mathrm{Mn(NO_3)_2}(aq) + 5 \mathrm{N}_2\mathrm{O}_4(g) + 4 \mathrm{H}_2\mathrm{O}(l) \) Reaction (b): \( 2 \mathrm{Mn(NO_3)_2}(s) \xrightarrow{450K} 2 \mathrm{MnO_2}(s) + 4 \mathrm{NO_2}(g) + \mathrm{O_2}(g) \) Reaction (c): \( 3 \mathrm{MnO_2}(s) \xrightarrow{700K} \mathrm{Mn}_3\mathrm{O}_4(s) + \frac{1}{2} \mathrm{O_2}(g) \) Reaction (d): \( 2 \mathrm{MnCl}_2(s) + 3 \mathrm{F}_2(g) \rightarrow 2 \mathrm{MnF}_3(s) + 2 \mathrm{ClF}_3(g) \)

Step-by-step solution

Reaction (a) - Manganese and Aqueous HNO₃

For the first reaction, manganese reacts with nitric acid to form Mn²⁺ ions and release NO₂ gas. The balanced equation is: \[ 2 \mathrm{Mn}(s) + 8 \mathrm{HNO}_3(aq) \rightarrow 2 \mathrm{Mn(NO_3)_2}(aq) + 5 \mathrm{N}_2\mathrm{O}_4(g) + 4 \mathrm{H}_2\mathrm{O}(l) \]

Reaction (b) - Decomposition of Manganese(II) Nitrate

For the second reaction, the decomposition of manganese(II) nitrate results in the formation of MnO₂ and release of NO₂ and O₂ gases. The balanced equation is: \[ 2 \mathrm{Mn(NO_3)_2}(s) \xrightarrow{450K} 2 \mathrm{MnO_2}(s) + 4 \mathrm{NO_2}(g) + \mathrm{O_2}(g) \]

Reaction (c) - Decomposition of MnO₂

For the third reaction, MnO₂ decomposes at 700 K to form Mn₃O₄. The balanced chemical equation is: \[ 3 \mathrm{MnO_2}(s) \xrightarrow{700K} \mathrm{Mn}_3\mathrm{O}_4(s) + \frac{1}{2} \mathrm{O_2}(g) \]

Reaction (d) - MnCl₂ Reacts with F₂(g)

For the last reaction, manganese(II) chloride reacts with fluorine gas to form manganese(III) fluoride and ClF₃. The balanced equation is: \[ 2 \mathrm{MnCl}_2(s) + 3 \mathrm{F}_2(g) \rightarrow 2 \mathrm{MnF}_3(s) + 2 \mathrm{ClF}_3(g) \] These are the balanced chemical equations for the various reactions involving elemental manganese as per the given information.

Key concepts

Elemental Manganese

Elemental manganese is a transition metal with the symbol Mn and atomic number 25. It is crucial in various chemical reactions due to its reactivity and ability to form different compounds. Manganese is often found in nature in combination with other elements, rather than in its pure form. In its elemental state, manganese appears as a hard, brittle, silvery-grey metal.
One interesting property of manganese is its ability to undergo redox reactions, meaning it can either donate or accept electrons. This feature makes it highly useful in various industrial and chemical processes.

• It is an essential trace element for living organisms, playing a critical role in bone formation, blood coagulation, and immune response.
• Manganese's reactivity with acid is notable; it reacts with substances like nitric acid ( HNO_3 ) to form soluble manganese compounds.

Manganese’s reactions in these exercises demonstrate how it can transform through different oxidation states, showcasing the versatility and importance of this elemental metal.

Decomposition Reactions

Decomposition reactions are a type of chemical reaction where a compound breaks down into simpler substances. These reactions require energy, often in the form of heat, light, or electricity. The energy input helps to break the chemical bonds within the compound.
In the context of manganese, we see decomposition in the form of thermal decomposition, where heat is the energy source. A characteristic reaction involves the decomposition of manganese(II) nitrate:\[ 2 \mathrm{Mn(NO_3)_2}(s) \xrightarrow{450K} 2 \mathrm{MnO_2}(s) + 4 \mathrm{NO_2}(g) + \mathrm{O_2}(g) \]

• This reaction highlights how manganese(II) nitrate decomposes into manganese dioxide, nitrogen dioxide, and oxygen when heated.
• Another decomposition reaction involves manganese dioxide decomposing to form manganese tetroxide:

\[ 3 \mathrm{MnO}_2(s) \xrightarrow{700K} \mathrm{Mn}_3\mathrm{O}_4(s) + \frac{1}{2} \mathrm{O}_2(g) \]Decomposition reactions are vital because they often lead to the formation of more stable compounds and are used in various applications, including material processing and manufacturing.

Chemical Reactions

Chemical reactions involve the transformation of reactants into products through the breaking and forming of chemical bonds. These reactions are fundamental to the study of chemistry and occur in everyday life. The aspect of balancing chemical equations is crucial to ensure that the law of conservation of mass is upheld, meaning the number of each type of atom must be the same on both sides of the equation.
For manganese, we explore both simple and complex reactions. An example of a simple reaction is manganese's direct reaction with nitric acid:\[ 2 \mathrm{Mn}(s) + 8 \mathrm{HNO}_3(aq) \rightarrow 2 \mathrm{Mn(NO}_3)_2(aq) + 5 \mathrm{N}_2\mathrm{O}_4(g) + 4 \mathrm{H}_2\mathrm{O}(l) \]

• Here, manganese reacts to form manganese(II) nitrate and nitrogen dioxide gas.
• In contrast, more complex reactions involving manganese typically happen at elevated temperatures, such as those in decomposition reactions.

Studying these reactions helps us understand the behavior of elements and how they interact to create more complex and useful materials.

Manganese Compounds

Manganese compounds are diverse and have significant application across many industries. Once elemental manganese reacts with other substances, it forms these compounds, exhibiting various properties depending on the oxidation state of manganese.
Manganese compounds can include:

• Manganese(II) nitrate – A soluble compound formed in reactions with nitric acid.
• Manganese dioxide (MnO₂) – Commonly used as a depolarizer in batteries.
• Manganese tetroxide (Mn₃O₄) – Often formed through decomposition at high temperatures.
• Manganese(III) fluoride (MnF₃) – A result of reactions such as with fluorine gas, highlighting manganese's ability to form varied anion groups.

These compounds showcase the chemical versatility of manganese and its compounds, which are used in industries ranging from steel production to battery manufacturing. Understanding manganese's compound formation and reactivity provides insights into how these materials can be utilized effectively.