The following are two reaction schemes involving magnesium. Scheme I: When magnesium burns in oxygen, a white solid (A) is formed. A dissolves in \(1 M \mathrm{HCl}\) to give a colorless solution (B). Upon addition of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) to \(\mathrm{B},\) a white precipitate is formed(C). On heating, C decomposes to \(D\) and a colorless gas is generated (E). When \(\mathrm{E}\) is passed through limewater [an aqueous suspension of \(\left.\mathrm{Ca}(\mathrm{OH})_{2}\right], \underline{\mathrm{a}}\) white precipitate appears (F). Scheme II:Magnesium reacts with \(1 M \mathrm{H}_{2} \mathrm{SO}_{4}\) to produce a colorless solution (G). Treating G with an excess of NaOH produces a white precipitate \((\mathrm{H}) . \mathrm{H}\) dissolves in \(1 M \mathrm{HNO}_{3}\) to form a colorless solution. When the solution is slowly evaporated, a white solid (I) appears. On heating I, a brown gas is given off. Identify \(\mathrm{A}-\mathrm{I}\) and write equations representing the reactions involved.

Step by step solution

01

Identify compound A

When magnesium burns in oxygen, a white solid (A) is formed. This reaction is known as combustion and produces magnesium oxide (\(MgO\)). Balanced equation: \(2 Mg + O_2 \rightarrow 2 MgO\)

02

Identify compound B

Compound A (\(MgO\)) then dissolves in \(1 M HCl\) to form a colorless solution (B). This results in the formation of magnesium chloride (\(MgCl_2\)) and water. Balanced equation: \(MgO + 2 HCl \rightarrow MgCl_2 + H_2O\)

03

Identify compound C

When sodium carbonate (\(Na_2CO_3\)) is added to compound B (\(MgCl_2\)), a white precipitate is formed (C). This precipitate is magnesium carbonate (\(MgCO_3\)). Balanced equation: \(MgCl_2 + Na_2CO_3 \rightarrow MgCO_3 + 2 NaCl\)

04

Identify compounds D and E

On heating, compound C (\(MgCO_3\)) decomposes to form compound D and a colorless gas E. Compound D is magnesium oxide (\(MgO\)), and gas E is carbon dioxide (\(CO_2\)). Balanced equation: \(MgCO_3 \rightarrow MgO + CO_2\)

05

Identify compound F

When the gas E (\(CO_2\)) is passed through limewater (\(Ca(OH)_2\)), a white precipitate F appears. This precipitate is calcium carbonate (\(CaCO_3\)). Balanced equation: \(Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O\)

06

Identify compound G

In scheme II, magnesium reacts with \(1 M H_2SO_4\) to produce a colorless solution (G). This reaction forms magnesium sulfate (\(MgSO_4\)). Balanced equation: \(Mg + H_2SO_4 \rightarrow MgSO_4 + H_2\)

07

Identify compound H

Treating compound G (\(MgSO_4\)) with an excess of NaOH produces a white precipitate \('H'\). This precipitate is magnesium hydroxide (\(Mg(OH)_2\)). Balanced equation: \(MgSO_4 + 2 NaOH \rightarrow Mg(OH)_2 + Na_2SO_4\)

08

Identify compound I

Compound H (\(Mg(OH)_2\)) dissolves in \(1 M HNO_3\) to form a colorless solution. When the solution is slowly evaporated, a white solid (I) appears. Compound I is magnesium nitrate (\(Mg(NO_3)_2\)). Balanced equation: \(Mg(OH)_2 + 2 HNO_3 \rightarrow Mg(NO_3)_2 + 2 H_2O\)

09

Identity the brown gas

On heating compound I (\(Mg(NO_3)_2\)), a brown gas is given off. This gas is nitrogen dioxide (\(NO_2\)). Balanced equation: \(2 Mg(NO_3)_2 \rightarrow 2 MgO + 4 NO_2 + O_2\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Combustion Reaction

A combustion reaction involves the rapid combination of a substance with oxygen to produce oxides and release energy, often in the form of heat and light. An everyday example is the burning of magnesium in oxygen to form magnesium oxide (\textbf{A}), as seen in the exercise. During this exothermic process, the white solid magnesium oxide is created with the release of energy. The balanced chemical equation for this reaction is:

\textbf{Reaction:} \[2 Mg + O_2 \rightarrow 2 MgO\]
In practical applications, combustion reactions are critical as they are the basis for propulsion in engines, production of energy in power plants, and even in fireworks for entertainment. The key concept to remember is that in a combustion reaction, a substance reacts with oxygen from the air and creates oxides as one of the products.

Precipitation Reaction

The precipitation reaction is a process where two soluble substances react in a solution to form an insoluble solid called a precipitate. In the provided problem, when sodium carbonate is added to the magnesium chloride solution, magnesium carbonate, which is insoluble in water, precipitates out (\textbf{C}). This type of reaction is essential for methods like gravimetric analysis in chemistry laboratory practices. The balanced equation that represents this reaction is:

\textbf{Reaction:} \[MgCl_2 + Na_2CO_3 \rightarrow MgCO_3(s) + 2 NaCl\]
This example highlights how ionic compounds can interact to form a new, insoluble compound. Precipitation reactions are widely used in water treatment, materials science, and as a way to remove unwanted ions from solutions in various industrial processes.

Decomposition Reaction

Decomposition reactions involve a single compound breaking down into two or more simpler substances. These reactions often require an input of energy, such as heat, light, or electricity. In the decomposition of magnesium carbonate (\textbf{C}) to magnesium oxide (\textbf{D}) and carbon dioxide (\textbf{E}), heat plays a crucial role in driving the reaction. Examining the given exercise:

\textbf{Reaction:} \[MgCO_3 \rightarrow MgO + CO_2\]
Decomposition reactions are fundamental both in academic studies and in many industrial processes. For example, they are used ore processing, the production of various chemicals, and even in the breakdown of biological matter. Understanding these reactions helps in fields ranging from metallurgy to environmental science.

Acid-Base Reaction

Acid-base reactions are characterized by the exchange of a proton (a hydrogen ion) between an acid and a base. When magnesium oxide (\textbf{B}) dissolves in hydrochloric acid, an acid-base reaction occurs, producing magnesium chloride and water. In another instance, magnesium reacts with sulfuric acid to generate magnesium sulfate and hydrogen gas in an acid-metal reaction. These are subtypes of acid-base reactions. Here are the balanced equations for these reactions:

\textbf{Reaction 1:} \[MgO + 2 HCl \rightarrow MgCl_2 + H_2O\]
\textbf{Reaction 2:} \[Mg + H_2SO_4 \rightarrow MgSO_4 + H_2\]
Acid-base reactions are widely used in titrations to determine concentrations, in buffering solutions to maintain pH, and for the generation of salts in chemical manufacturing. These reactions are pivotal in biological systems, industrial processes, and environmental chemistry.