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) \(\mathrm{Mg}(\mathrm{OH})_{2}, \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{MgCO}_{3}, \mathrm{H}_{2} \mathrm{O}, \mathrm{CO}_{2}\) (d) \(\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}, \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The products are \( \mathrm{MgCO_3} \), \( \mathrm{CO_2} \), and \( \mathrm{H_2O} \), which corresponds to option (c).

Step 1: Identify the Chemical Formula

Magnesium bicarbonate is represented by the chemical formula \( \mathrm{Mg(HCO_3)_2} \). We'll be examining the decomposition of this compound when an aqueous solution of it is boiled.

Step 2: Understand the Decomposition Reaction

Upon heating, \( \mathrm{Mg(HCO_3)_2} \) decomposes. The general reaction for bicarbonates when heated is that they decompose into carbonates, water, and carbon dioxide.

Step 3: Write the Decomposition Equation

The balanced chemical equation for the decomposition of magnesium bicarbonate when heated is:\[ \mathrm{Mg(HCO_3)_2 (aq) \rightarrow MgCO_3 (s) + CO_2 (g) + H_2O (l)} \]

Step 4: Determine the Products

From the balanced equation, when magnesium bicarbonate is boiled, the products formed are magnesium carbonate (\( \mathrm{MgCO_3} \)), carbon dioxide (\( \mathrm{CO_2} \)), and water (\( \mathrm{H_2O} \)).

Key Concepts

Chemical Reactions

Chemical reactions are processes by which substances interact to form new products. These transformations involve breaking chemical bonds in the reactants and forming new bonds in the products. In the case of magnesium bicarbonate, it undergoes a decomposition reaction when heated. Here, we start with a compound containing magnesium, hydrogen, carbon, and oxygen, and, as a result of heating, we obtain different substances.

The process involves the rearrangement of atoms in the reactants (\( \mathrm{Mg(HCO_3)_2} \)) to form new products such as magnesium carbonate (\( \mathrm{MgCO_3} \)), carbon dioxide (\( \mathrm{CO_2} \)), and water (\( \mathrm{H_2O} \)). This transformation highlights the nature of chemical reactions, where heat or other forms of energy can drive the conversion of substances into entirely new compounds.

Bicarbonate Decomposition

Bicarbonate decomposition occurs when bicarbonates are heated and break down into carbonates, carbon dioxide, and water. This type of reaction is a typical characteristic of metal bicarbonates like magnesium bicarbonate. When heated, the unstable bicarbonate compound loses carbon dioxide molecules and water, leaving behind a carbonate compound.

For magnesium bicarbonate, this decomposition can be represented in a chemical equation: \[\mathrm{Mg(HCO_3)_2 (aq) \rightarrow MgCO_3 (s) + CO_2 (g) + H_2O (l)}\]

• \( \mathrm{MgCO_3} \) (Solid Magnesium Carbonate): Forms as a precipitate, appearing as a solid at the bottom of the solution.
• \( \mathrm{CO_2} \) (Gaseous Carbon Dioxide): Released as bubbles or vapor.
• \( \mathrm{H_2O} \) (Liquid Water): Remains in the solution.

This tendency of bicarbonates to release carbon dioxide makes them useful for identifying metal ions in various tests, as they undergo distinct reactions with heat.

Aqueous Solution Reactions

Aqueous solution reactions involve substances that are dissolved in water. In such reactions, compounds break down and rearrange in the presence of water. Magnesium bicarbonate is a soluble compound when dissolved in water, allowing it to undergo decomposition upon heating.

The presence of water in the reaction is crucial because it helps to stabilize certain products and enable the reaction to proceed efficiently. In an aqueous solution, ions are free to move and react, which is why heating the solution facilitates the decomposition of magnesium bicarbonate.

• The water allows the release and collection of \( \mathrm{CO_2} \) gas in the reaction.
• It keeps \( \mathrm{MgCO_3} \) in contact with other ions present in the solution, enabling the formation of solids and gases.
• In this setting, water acts as both a solvent and a product, showcasing its integral role in the decomposition.

Recognizing the behavior of substances in aqueous solutions is essential for predicting reaction outcomes and understanding the conditions under which reactions occur.