Problem 81 - A Complete Resource Book in Chemistry for JEE Main

Question

When chlorine is passed over dry slaked lime at room temperature, the main reaction product is (a) \(\mathrm{CaCl}_{2}\) (b) \(\mathrm{Ca}(\mathrm{OCl})_{2}\) (c) \(\mathrm{Ca}\left(\mathrm{ClO}_{2}\right)_{2}\) (d) \(\mathrm{CaOCl}_{2}\)

Step-by-Step Solution

Answer

(d) \(\mathrm{CaOCl}_{2}\) is the main product.

Step 1: Understanding Reaction Conditions

The problem involves passing chlorine over dry slaked lime at room temperature. Slaked lime is chemically represented as calcium hydroxide, \[ \text{Ca(OH)}_2 \]. The reaction condition is room temperature.

Step 2: Writing the Chemical Equation

The chemical reaction for chlorine reaction with dry slaked lime is:\[ \text{2Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O} \]Calcium hypochlorite \(\text{Ca(OCl)}_2 \) and calcium chloride \(\text{CaCl}_2\) along with water are the products.

Step 3: Identifying the Main Product

The main product commonly associated with mixing chlorine and slaked lime is calcium oxychloride, better known as bleaching powder. It is represented as \(\text{CaOCl}_2\), often simplified from its precursor products \( \text{Ca(OCl)}_2\) and \(\text{CaCl}_2\).

Step 4: Choosing the Correct Option

Given the options, and knowing that calcium oxychloride or bleaching powder is the main product, option (d) \( \text{CaOCl}_2 \) is the correct answer.

Key Concepts

Chlorine Reactions

Chlorine is a highly reactive chemical element, known for its ability to form compounds with many different elements. When chlorine gas is passed over certain substances, it typically undergoes a substitution or addition reaction. In the context of the exercise, chlorine is reacting with dry slaked lime. Here, slaked lime functions as the base that reacts with chlorine to produce calcium oxychloride, also commonly referred to as bleaching powder.

The chemical reaction proceeds as follows: the chlorine molecules (\[ \text{Cl}_2 \]) interact with calcium hydroxide (\[ \text{Ca(OH)}_2 \]), the dry slaked lime, which leads to the production of a combination of calcium hypochlorite (\[ \text{Ca(OCl)}_2 \]) and calcium chloride (\[ \text{CaCl}_2 \]). Along with these products, water (\[ \text{H}_2\text{O} \]) is also formed. This set of reactions underlines the versatility of chlorine in forming compounds and highlights its usefulness in industrial applications, such as the production of bleaching powder.

• Substitution reactions often involve the replacement of one atom or group of atoms in a molecule with another.
• Addition reactions typically involve the merging of two or more reactants to form a single product.

Calcium Hydroxide Chemistry

Calcium hydroxide, also known as slaked lime, is a white powder derived by hydrating quicklime. Its chemical formula is \[ \text{Ca(OH)}_2 \], which reveals it contains calcium ions bonded to hydroxide ions. This compound is notable for its alkalinity and reactivity, making it quite beneficial in many chemical reactions, including the formation of bleaching powder.

In chemical reactions, calcium hydroxide can behave as a base because it can donate hydroxide ions. This characteristic allows it to neutralize acids and participate actively in the formation of compounds. When chlorine is involved, the reactivity of calcium hydroxide is crucial, as it facilitates the formation of bleaching powder, thereby exemplifying its utility in chemical manufacturing processes.

• Calcium hydroxide plays a critical role in water treatment, helping to remove impurities and kill bacteria.
• It also aids in soil stabilization for construction projects due to its alkaline nature.

Bleaching Powder Production

Bleaching powder is a significant chemical product, widely used for its powerful disinfecting properties. Its production primarily involves the interaction of chlorine with calcium hydroxide, resulting in a mixture of chemical compounds. This mixture predominantly includes calcium oxychloride, commonly focused on in the context of producing "bleaching powder."

During its production process, the chemical reaction with chlorine transforms calcium hydroxide into calcium hypochlorite (\[ \text{Ca(OCl)}_2 \]), one of the key ingredients in bleaching powder. Additionally, calcium chloride (\[ \text{CaCl}_2 \]) is another product that is formed. Despite being a blend of these compounds, calcium oxychloride is the primary substance often referred to when mentioning bleaching powder. It is denoted as \[ \text{CaOCl}_2 \], highlighting the oxygen component which is crucial in its bleaching capability.

Bleaching powder serves an important role not only in bleaching textiles but also for:

• Disinfection of drinking water due to its ability to kill bacteria and viruses.
• Use in the chemical industry as an oxidizing agent in processes like odor removal and chlorine substitution reactions.