Problem 5 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is formed when sodium sulphate is boiled with powered sulphur? (a) \(\mathrm{NaHSO}_{4}\) (b) \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}\)

Step-by-Step Solution

Answer

The compound formed is \(\text{Na}_2 \text{S}_2\text{O}_3\). Option (b).

Step 1: Identify the Chemical Reaction

When sodium sulphate (\(\text{Na}_2\text{SO}_4\)) is boiled with powdered sulphur, a chemical reaction occurs. It is important to understand the typical reactivity of sulfur with sulfate ions to predict the resulting compounds.

Step 2: Write the Chemical Equation

The reaction between sodium sulphate and sulfur generally leads to the formation of sodium thiosulphate. The reaction is: \[ \text{Na}_2\text{SO}_4 + 2 \text{S} \rightarrow \text{Na}_2\text{S}_2\text{O}_3 \] Here, sodium sulphate reacts with additional sulfur to form sodium thiosulphate (\(\text{Na}_2 \text{S}_2\text{O}_3\)).

Step 3: Determine the Correct Option

Compare the product \(\text{Na}_2 \text{S}_2\text{O}_3\) obtained from the reaction to the given options: (a) \(\text{NaHSO}_4\), (b) \(\text{Na}_2 \text{S}_2 \text{O}_3\), (c) \(\text{Na}_2 \text{SO}_4\), (d) \(\text{Na}_2 \text{S}_4 \text{O}_6\). The correct match is option (b) \(\text{Na}_2 \text{S}_2\text{O}_3\).

Key Concepts

Sodium Thiosulphate Formation

Sodium thiosulphate is a fascinating compound with a variety of uses, ranging from photography to medicine. Its formation involves a chemical reaction where sodium sulphate reacts with sulfur. When sodium sulphate (\(\text{Na}_2\text{SO}_4\)) is combined with powdered sulfur and heated, sodium thiosulphate (\(\text{Na}_2\text{S}_2\text{O}_3\)) is produced through a typical dry reaction.
Sodium thiosulphate is often used in iodometry, a type of titration in analytical chemistry, due to its ability to reduce iodine to iodide. Its formation is straightforward when understanding the reaction components: sodium sulphate provides the sulfate ions, and additional sulfur atoms add to form thiosulfate ions.

• Sodium thiosulphate can help neutralize chlorine in swimming pools or aquarium setups.
• In the photography industry, it acts as a fixer to dissolve unreacted silver halides on photographic films.

This compound is a prime example of how sulfur, an element with various oxidation states, can engage in reactions leading to useful products.

Chemical Reactions with Sulfur

Sulfur is a highly reactive non-metal that can engage in numerous chemical reactions, resulting in a wide variety of compounds. When it reacts with other elements or compounds, like sodium sulphate, the outcomes can be quite intriguing.

• Sulfur can change its form depending on conditions, easily converting from one allotrope to another, including rhombic and monoclinic forms.
• Being a part of Group 16 on the periodic table, sulfur often forms compounds by gaining electrons to become an anion, but it can also form compounds in which it shares electrons, as seen in its reaction with sodium sulphate.

In the specific reaction between sodium sulphate and sulfur, sulfur adds additional atoms to the sulfate ions, transforming them into thiosulfate ions. This type of reaction is significant because it highlights sulfur's unique ability to form bonds and create different types of sulphates, ranging from simple to complex structures further illustrating the vast chemistry of sulfur.

Sodium Sulphate Chemical Preparation

Sodium sulphate is typically produced through various industrial methods and sometimes occurs naturally as well. It's a key ingredient in many chemical processes due to its moderate reactivity.
One common method of preparing sodium sulphate involves the reaction of sodium chloride with sulfuric acid, producing sodium sulphate and hydrochloric acid as its by-products. \[\text{2NaCl + H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{HCl}\]

• Sodium sulphate can naturally be found in the form of minerals, such as thenardite and mirabilite, offering a sustainable source.
• Industrially, its preparation is vital for the manufacturing of detergents, paper, and glass as it helps in the controlled release of water in the drying process.

Understanding sodium sulphate's preparation is crucial for its applications across various industries, ensuring efficiency in the production of numerous everyday products.