Problem 67 - A Complete Resource Book in Chemistry for JEE Main

Question

What are the products formed when an aqueous solution of magnesium bicarbonate is boiled? (a) \(\mathrm{Mg}, \mathrm{CO}_{2}, \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Mg}(\mathrm{OH})_{2}^{2}, \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{MgCO}_{3}, \mathrm{H}_{2} \mathrm{O}, \mathrm{CO}_{2}\) (d) \(\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}, \mathrm{H}_{2} \mathrm{O}^{2}\)

Step-by-Step Solution

Answer

The correct answer is (c) \( \mathrm{MgCO}_3, \mathrm{H}_2\mathrm{O}, \mathrm{CO}_2 \).

Step 1: Understanding the Reaction

When an aqueous solution of magnesium bicarbonate is heated or boiled, the bicarbonate ion ( ext{HCO}_3^- ) decomposes. This decomposition results in the formation of magnesium carbonate ( ext{MgCO}_3), water ( ext{H}_2 ext{O}), and carbon dioxide ( ext{CO}_2).

Step 2: Writing the Chemical Equation

The decomposition reaction can be written as follows: \[ ext{Mg(HCO}_3)_2(aq) \xrightarrow{heat} \text{MgCO}_3(s) + ext{H}_2 ext{O}(l) + ext{CO}_2(g) \] This equation shows the products formed when magnesium bicarbonate solution is boiled.

Step 3: Comparing with Given Options

Let's compare the reaction products  ext{MgCO}_3,  ext{H}_2 ext{O}, and  ext{CO}_2 with the given options: (a)  ext{Mg}, ext{CO}_2, ext{H}_2 ext{O} (b)  ext{Mg(OH)}_2, ext{H}_2 ext{O} (c)  ext{MgCO}_3, ext{H}_2 ext{O}, ext{CO}_2 (d)  ext{Mg(HCO}_3)_2, ext{H}_2 ext{O}^2 Option (c) matches the products obtained by boiling magnesium bicarbonate:  ext{MgCO}_3,  ext{H}_2 ext{O}, and  ext{CO}_2.

Key Concepts

Magnesium Bicarbonate

Magnesium bicarbonate is a chemical compound that exists commonly in aqueous solutions. You won't find it as a solid at room temperature because it's unstable and breaks down in water. Magnesium bicarbonate forms when magnesium ions (Mg\(^{2+}\)) interact with bicarbonate ions (HCO\(^{-}_3\)). This reaction often takes place in natural waters like lakes and rivers, where limestone (calcium bicarbonate) and dolomite minerals dissolve.

This compound tends to decompose easily, especially when heated. You'll rarely find stable solid magnesium bicarbonate. It plays an important role in natural water systems, acting as a buffer that helps maintain pH levels. When heated, it converts into other forms, which is why you'll see different products from its decomposition.

Chemical Equation

Chemical equations are a way to represent chemical reactions through the use of symbols. They inform us about the substances involved, including both the reactants and the products. Understanding chemical equations is crucial in studying chemistry because it allows scientists to convey reactions in a clear, concise manner.

In the case of magnesium bicarbonate undergoing decomposition, the chemical equation is written as:\[ \text{Mg(HCO}_3)_2(aq) \xrightarrow{\text{heat}} \text{MgCO}_3(s) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \]
This equation tells us what happens when we apply heat to an aqueous solution of magnesium bicarbonate. The products include magnesium carbonate (MgCO\(_3\)), water (H\(_2\)O), and carbon dioxide (CO\(_2\)). Each component is represented with its state, such as solid (s), liquid (l), aqueous (aq), or gas (g).

Recognizing how to read and write chemical equations is fundamental in predicting the outcome of reactions, as well as understanding the processes occurring at the molecular level.

Thermal Decomposition

Thermal decomposition is a type of chemical reaction where a compound breaks down into multiple smaller constituents when heat is applied. This type of reaction is common in various substances including magnesium bicarbonate. Thermal decomposition allows us to tap into the unique properties and uses of compounds when subjected to different conditions.

When magnesium bicarbonate is heated, the compound decomposes into magnesium carbonate, water, and carbon dioxide. This process illustrates how heat can drive changes at the molecular level. Thermal decomposition often requires energy input, such as heat, to break chemical bonds within the compound. During this reaction:

• The magnesium bicarbonate (Mg(HCO\(_3\))\(_2\)) decomposes because the heat provokes instability.
• Magnesium carbonate (MgCO\(_3\)), a solid substance, forms as one of the products.
• Carbon dioxide (CO\(_2\)) is released as a gas, which may escape into the air.
• Water (H\(_2\)O) is released in liquid form.

Understanding thermal decomposition helps chemists create and innovate processes in industries like manufacturing and environmental science.