Problem 42 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Mention the products formed in the following : (i) Chlorine gas is bubbled through a solution of ferrous bromide. [1986-1 Mark] (ii) Iodine is added to a solution of stannous chloride. [1986-1 Mark]

Step-by-Step Solution

Answer

(i) FeCl₂ and Br₂. (ii) SnCl₄ and I⁻.

Step 1: Identify Reactants for Reaction (i)

We have chlorine gas (Cl₂) reacting with an aqueous solution of ferrous bromide (FeBr₂). The reactants are Cl₂ and FeBr₂.

Step 2: Predict the Reaction (i) Type

This is a single displacement reaction where chlorine, a halogen, displaces the bromine from ferrous bromide, forming ferrous chloride (FeCl₂) and bromine gas (Br₂) as products.

Step 3: Write Balanced Chemical Equation for Reaction (i)

The balanced chemical equation is: \[ \text{Cl}_2 + 2 \text{FeBr}_2 \rightarrow 2 \text{FeCl}_2 + \text{Br}_2 \] where chlorine replaces bromine in ferrous bromide.

Step 4: Identify Reactants for Reaction (ii)

In this case, iodine (I₂) is added to an aqueous solution of stannous chloride (SnCl₂). The reactants are I₂ and SnCl₂.

Step 5: Predict the Reaction (ii) Type

This reaction is a redox reaction. The iodine oxidizes stannous chloride to form stannic chloride (SnCl₄) and iodide ions (I⁻).

Step 6: Write Balanced Chemical Equation for Reaction (ii)

The balanced equation for the reaction is: \[ \text{I}_2 + \text{SnCl}_2 \rightarrow \text{SnCl}_4 + 2\text{I}^- \] showing that iodine is reduced and stannous chloride is oxidized.

Key Concepts

Single Displacement Reaction

When discussing chemical reactions, one important type is the single displacement reaction. In this kind of reaction, an element displaces another element from a compound. This usually involves one element being more reactive than the other. For example, in the exercise given, chlorine gas is able to displace bromine from ferrous bromide because chlorine is more reactive than bromine. As a result, chlorine and ferrous bromide react to form ferrous chloride and bromine gas.

Key points to remember:

• In a single displacement reaction, a more reactive element displaces a less reactive element in a compound.
• This type of reaction is often seen in metals and halogens.
• An example reaction: \[ \text{Cl}_2 + 2 \text{FeBr}_2 \rightarrow 2 \text{FeCl}_2 + \text{Br}_2 \]

The activity series chart often helps to determine which element can displace which. In the case of halogens, the order is Fluorine > Chlorine > Bromine > Iodine, with fluorine being the most reactive. Understanding this chart is crucial when predicting outcomes in single displacement reactions.

Redox Reaction

Redox reactions are a fundamental concept in chemistry, where reduction and oxidation occur simultaneously. It's like a chemical dance where one molecule gives up electrons and gets oxidized, while another gains those electrons and gets reduced.

For example, consider when iodine is added to stannous chloride, a redox reaction takes place. Here, iodine molecules (\(\text{I}_2\)) are reduced to iodide ions (\(\text{I}^-\)) while stannous chloride is oxidized to form stannic chloride (\(\text{SnCl}_4\)). Let's break it down:

• Reduction: Iodine goes from a 0 oxidation state in \(\text{I}_2\) to a -1 state in \(\text{I}^-\).
• Oxidation: Tin goes from a +2 oxidation state in \(\text{SnCl}_2\) to a +4 state in \(\text{SnCl}_4\).

The balanced equation of this redox reaction is \[ \text{I}_2 + \text{SnCl}_2 \rightarrow \text{SnCl}_4 + 2\text{I}^- \]. In redox reactions, keeping track of electron transfer is key to understanding what's happening.

Balanced Chemical Equations

Balanced chemical equations are a crucial part of chemistry as they ensure that atoms are conserved during a reaction. The law of conservation of mass dictates that in any given closed system, the mass remains constant, meaning the number of atoms for each element in the reactants must equal the number in the products.

A balanced equation makes this possible by appropriately adjusting the coefficients. For instance, consider the equation for the chlorine and ferrous bromide reaction: \[ \text{Cl}_2 + 2 \text{FeBr}_2 \rightarrow 2 \text{FeCl}_2 + \text{Br}_2 \]. Notice how there are two iron (Fe) atoms and two bromine (Br) molecules both in reactants and products, ensuring balance.

Similarly, in the redox reaction of iodine and stannous chloride: \[ \text{I}_2 + \text{SnCl}_2 \rightarrow \text{SnCl}_4 + 2\text{I}^- \], the equation is balanced because it reflects the conservation of iodine and chlorine atoms.

Remember these tips:

• Adjust equation coefficients, not subscripts, to balance equations.
• Ensure atoms of each type match in both reactants and products.
• Verify both mass and charge balance, especially in redox equations.

Properly balanced equations not only satisfy the law of conservation of mass but also give a clear picture of the reaction's stoichiometry.