Problem 54 - A Complete Resource Book in Chemistry for JEE Main

Question

The reaction of slaked lime with \(\mathrm{Cl}_{2} \mathrm{gas}\) gives (a) a mixture of \(\mathrm{Ca}(\mathrm{OCl})_{2}, \mathrm{Ca}(\mathrm{OH}), \mathrm{CaCl}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) (b) quick lime (c) Baryta water (d) only \(\mathrm{Ca}(\mathrm{OCl})_{2}\)

Step-by-Step Solution

Answer

Option (a) a mixture of \( \text{Ca(OCl)}_2, \text{Ca(OH)}_2, \text{CaCl}_2 \), and \( \text{H}_2\text{O} \).

Step 1: Identify the Reactants and Products

We are starting with the reactants slaked lime (which is chemically known as calcium hydroxide, \( \text{Ca(OH)}_2 \)) and chlorine gas (\( \text{Cl}_2 \)). The problem asks us to determine the possible products of this reaction.

Step 2: Write the Chemical Equation for the Reaction

The reaction of calcium hydroxide with chlorine gas produces calcium hypochlorite \( \text{Ca(OCl)}_2 \), calcium chloride \( \text{CaCl}_2 \), and water \( \text{H}_2\text{O} \). The balanced chemical equation is:\[2 \text{Ca(OH)}_2 + 2 \text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2 \text{H}_2\text{O}\]

Step 3: Analyze the Products Formed

According to the balanced chemical reaction, the products are calcium hypochlorite (\( \text{Ca(OCl)}_2 \)), calcium chloride (\( \text{CaCl}_2 \)), and water (\( \text{H}_2\text{O} \)). There is no excess calcium hydroxide left because it reacts completely and no other compounds such as quick lime or baryta water are produced.

Step 4: Match with Given Options

From the chemical equation, we have collinear products: \( \text{Ca(OCl)}_2 \), \( \text{CaCl}_2 \), and \( \text{H}_2\text{O} \). To select the matching option from (a) a mixture of \( \text{Ca(OCl)}_2, \text{Ca(OH)}_2, \text{CaCl}_2 \) and \( \text{H}_2\text{O} \); (b) quick lime; (c) Baryta water; (d) only \( \text{Ca(OCl)}_2 \), the correct option that reflects the products is option (a).

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is a fundamental skill in chemistry. It allows us to depict a reaction accurately by ensuring that the number of atoms for each element is the same for both reactants and products. This means following the law of conservation of mass, which tells us that matter is neither created nor destroyed in a chemical reaction.

When we say an equation is balanced, we mean that the same number of each type of atom appears on both sides of the equation. For example, in the reaction between calcium hydroxide (\(\text{Ca(OH)}_2\)) and chlorine gas (\(\text{Cl}_2\)), the balanced equation is:

• Reactants: \(2 \text{Ca(OH)}_2 + 2 \text{Cl}_2\)
• Products: \(\text{Ca(OCl)}_2 + \text{CaCl}_2 + 2 \text{H}_2\text{O}\)

This shows that for every two molecules of chlorine gas and two units of slaked lime, we produce one molecule of calcium hypochlorite, one molecule of calcium chloride, and two molecules of water. Keeping track of how many of each atom is on either side helps ensure the equation is correctly balanced.

Reaction Products

In chemical reactions, the substances that are formed are called the products. Determining what products form from given reactants requires understanding of chemical behavior and sometimes even previous experiments. In the case of slaked lime reacting with chlorine gas, the products are calcium hypochlorite (\(\text{Ca(OCl)}_2\)), calcium chloride (\(\text{CaCl}_2\)), and water (\(\text{H}_2\text{O}\)).

These products arise from the complex interactions of the atoms and molecules involved in the reaction. Here's a breakdown of the products:

• Calcium Hypochlorite \(\text{Ca(OCl)}_2\): Often used in sanitizing and bleaching, calcium hypochlorite is one part of the mixture produced.
• Calcium Chloride \(\text{CaCl}_2\): This salt helps stabilize the hypochlorite compound.
• Water \(\text{H}_2\text{O}\): A common product in many reactions, water forms as a result of the hydrogen and oxygen.

This understanding of chemical products helps predict behavior and outcomes in practical applications.

Slaked Lime

Slaked lime, chemically known as calcium hydroxide (\(\text{Ca(OH)}_2\)), is a substance created by adding water to quicklime (calcium oxide). It is an important chemical in various industries, including construction and water treatment.

The chemical properties of slaked lime make it useful for a range of applications:

• Neutralization: Its alkaline nature allows it to neutralize acids, making it useful in treating industrial waste.
• Water Treatment: By softening water and removing impurities, slaked lime can help ensure clean drinking water.
• Building Materials: Used in mortar and plaster, it helps in constructions and renovations.

When slaked lime reacts with chlorine gas, it forms compounds useful in disinfection, showcasing its versatility. Understanding properties like these is key in leveraging chemical reactions for practical uses.