Problem 28 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

State with balanced equations what happens when : (i) Aluminium sulphide gives a foul odour when it becomes damp. Write a balanced chemical equation for the reaction. [1997 - 2 Marks] (ii) Reaction of aluminium with aqueous sodium hydroxide.

Step-by-Step Solution

Answer

(i) \(\text{Al}_2\text{S}_3 + 6\text{H}_2\text{O} \rightarrow 2\text{Al(OH)}_3 + 3\text{H}_2\text{S}\). (ii) \(2\text{Al} + 2\text{NaOH} + 6\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 + 3\text{H}_2\).

Step 1: Understanding Aluminum Sulphide in Water

When aluminum sulphide \(\text{(Al}_2\text{S}_3)\) becomes damp, it reacts with water to produce hydrogen sulfide \(\text{(H}_2\text{S})\) which has a characteristic foul odor. We will write the balanced chemical equation for this reaction in the next step.

Step 2: Writing the Balanced Equation for Foul Odor

The reaction can be represented as:\[\text{Al}_2\text{S}_3 (s) + 6\text{H}_2\text{O} (l) \rightarrow 2\text{Al} (\text{OH})_3 (s) + 3\text{H}_2\text{S} (g)\]This equation shows that aluminum sulphide reacts with water to form aluminum hydroxide and hydrogen sulfide gas, which is responsible for the foul odor.

Step 3: Reaction of Aluminum with Aqueous Sodium Hydroxide

Aluminum reacts with aqueous sodium hydroxide to produce sodium aluminate and hydrogen gas. The balanced chemical equation for this reaction is:\[2\text{Al} (s) + 2\text{NaOH} (aq) + 6\text{H}_2\text{O} (l) \rightarrow 2\text{NaAl} (\text{OH})_4 (aq) + 3\text{H}_2 (g)\]This equation represents the formation of sodium tetrahydroxoaluminate and the release of hydrogen gas.

Key Concepts

Balanced Chemical Equations

Balancing chemical equations is a crucial skill in chemistry. It helps to ensure that the same number of each type of atom appears on both sides of the equation, which reflects the conservation of mass.

• Look at the original and resulting compounds and count the atoms for each element involved.
• Add coefficients - the numbers in front of compounds - to balance the number of each atom on both sides.

For example, the balanced equation for the reaction of aluminum sulfide with water is: \[ \text{Al}_2\text{S}_3 (s) + 6\text{H}_2\text{O} (l) \rightarrow 2\text{Al} \text{(OH)}_3 (s) + 3\text{H}_2\text{S} (g) \] Each side of the equation now has:- 2 aluminum atoms- 3 sulfur atoms- 12 hydrogen atoms- 6 oxygen atomsBalancing chemical equations takes practice, but remember: each step brings you closer to understanding how chemical reactions work.

Aluminium Reactions

Aluminum is a versatile metal that reacts with other compounds in interesting ways. One common reaction is with sodium hydroxide (NaOH), an important industrial chemical.In this reaction, aluminum reacts with aqueous sodium hydroxide to form sodium aluminate and hydrogen gas, shown by:\[ 2\text{Al} (s) + 2\text{NaOH} (aq) + 6\text{H}_2\text{O} (l) \rightarrow 2\text{NaAl} \text{(OH)}_4 (aq) + 3\text{H}_2 (g) \] The aluminum undergoes a transformation, forming sodium tetrahydroxoaluminate, and hydrogen gas is released as a byproduct.

• Sodium hydroxide helps to dissolve the protective oxide layer on aluminum, allowing the reaction to proceed.
• Hydrogen gas, produced in the reaction, is a lightweight, energy-rich gas often used as a fuel.

This aluminum-sodium hydroxide reaction is a great example of a metal dissolving in a base, which might seem unusual since metals typically react with acids.

Hydrogen Sulfide Odor

Hydrogen sulfide (H₂S) is known for its distinct rotten egg smell, a trait easily noticeable even in small quantities. Understanding its formation and properties is essential.This foul-smelling gas is released when aluminum sulfide reacts with water:\[ \text{Al}_2\text{S}_3 (s) + 6\text{H}_2\text{O} (l) \rightarrow 2\text{Al} \text{(OH)}_3 (s) + 3\text{H}_2\text{S} (g) \] Hydrogen sulfide has some noteworthy characteristics:

• It's a colorless gas with a strong odor similar to rotten eggs
• Although it's toxic and flammable, small amounts are often detectable because of its strong smell
• H₂S is often encountered in the breakdown of organic matter, such as in swamps and sewers.

Understanding H₂S’s properties can prepare you for handling situations where this reactive and odorous gas is present.