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 formed are \(\mathrm{MgCO}_{3}, \mathrm{H}_{2} \mathrm{O}, \mathrm{CO}_{2}\) (option c).

Step 1: Write the Chemical Reaction

When an aqueous solution of magnesium bicarbonate is boiled, it undergoes a decomposition reaction. Magnesium bicarbonate ( \( \mathrm{Mg(HCO_3)_2} \) ) decomposes into magnesium carbonate ( \( \mathrm{MgCO_3} \) ), water ( \( \mathrm{H_2O} \) ), and carbon dioxide ( \( \mathrm{CO_2} \) ).The balanced chemical equation is: \[ \mathrm{Mg(HCO_3)_2} \rightarrow \mathrm{MgCO_3} + \mathrm{H_2O} + \mathrm{CO_2} \]

Step 2: Analyze the Reaction

In the reaction, each magnesium bicarbonate molecule breaks down into one magnesium carbonate molecule, one water molecule, and one carbon dioxide molecule. This is a typical decomposition reaction seen with bicarbonates upon heating.

Step 3: Identify the Correct Answer

From the options given, we need to find the set of products that matches the reaction we have analyzed. The products are Magnesium Carbonate (\( \mathrm{MgCO_3} \)), Water (\( \mathrm{H_2O} \)), and Carbon Dioxide (\( \mathrm{CO_2} \)). This corresponds to option (c).

Key Concepts

Magnesium Bicarbonate

Magnesium bicarbonate is a chemical compound with the formula \( \mathrm{Mg(HCO_3)_2} \). It is an unstable compound that mainly exists in its aqueous (water-based) solution. The compound is part of the bicarbonates family, which means it consists of the bicarbonate ions combined with a metal—in this case, magnesium. The presence of magnesium bicarbonate is crucial in many natural and industrial processes. In nature, it can be found in spring waters, contributing to the hardness of water. When it is exposed to heat, magnesium bicarbonate readily transforms into more stable compounds. This property makes it useful but also requires careful handling, especially in chemical processes.This compound is particularly interesting due to its role in the decomposition that results in the formation of other useful substances. When describing magnesium bicarbonate, it's important to note its dual function:

• As a source of magnesium ions, which are chemically reactive.
• As a subject to chemical changes, especially thermal decomposition, which we'll explore further.

So, understanding its properties helps in predicting the outcomes of heating an aqueous solution containing this compound.

Thermal Decomposition

Thermal decomposition refers to the process where a compound breaks down into simpler substances when heated. In this context, when magnesium bicarbonate undergoes thermal decomposition, it produces magnesium carbonate, water, and carbon dioxide. The process follows typical decomposition reaction behavior. It starts with heating, which provides the energy needed for the chemical bonds in magnesium bicarbonate to break apart. Once these bonds are broken, magnesium carbonate (\( \mathrm{MgCO_3} \)), water (\( \mathrm{H_2O} \)), and carbon dioxide (\( \mathrm{CO_2} \)) form as products.Highlighting some characteristics of this reaction:

• It requires the input of energy (heat) to occur.
• It results in products that are more stable than the original compound.
• It typically involves a gas being released, in this case, carbon dioxide.

This type of reaction is quite common in chemistry, especially when dealing with carbonates or bicarbonates. Knowing how thermal decomposition works, especially in baking or in the manufacture of cement and lime, provides valuable insight into practical applications of chemistry.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They describe how reactants transform into products, providing important information about what occurs during the reaction. In the case of magnesium bicarbonate's decomposition, the equation is:\[ \mathrm{Mg(HCO_3)_2} \rightarrow \mathrm{MgCO_3} + \mathrm{H_2O} + \mathrm{CO_2} \]Here, reactants (on the left side) transform into products (on the right side). The arrow signifies the direction of the reaction, showing that magnesium bicarbonate breaks down into magnesium carbonate, water, and carbon dioxide when heated.Chemists use equations like this to understand and predict what substances are formed and in what proportions. Key aspects of chemical equations include:

• The compounds involved, represented by their chemical formulas.
• The proportions of each compound, indicated by coefficients (although in this reaction, the coefficients are all implicitly one).
• The physical state of compounds (e.g., solid, liquid, gas) is often included, though not essential for understanding the basic stoichiometry.

Understanding chemical equations allows us to grasp the "story" of a reaction, from start to finish, making them an invaluable tool in chemistry for both study and practical application.