Problem 52 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is not correct? (a) ozone is used to identify the presence of unsaturation in alkenes (b) sodium thiosulphate reacts with iodine to form sodium suphate (c) iodine oxidizes sodium thiosulphate to sodium tetrathionate (d) sodium thiosulphate is soluble in water

Step-by-Step Solution

Answer

Option (b) is not correct.

Step 1: Understanding Each Option

Read each option carefully. - (a) Ozone is used in ozonolysis, where it reacts with alkenes to identify unsaturation by breaking double bonds. This statement is correct. - (b) Sodium thiosulphate does not react with iodine to form sodium sulphate; it forms sodium tetrathionate and sodium iodide. This statement is incorrect. - (c) Iodine oxidizes sodium thiosulphate to sodium tetrathionate, indeed forming sodium tetrathionate and sodium iodide, so this statement is correct. - (d) Sodium thiosulphate is soluble in water, making this statement correct as well.

Step 2: Identifying the Incorrect Statement

Based on the evaluations from Step 1, the incorrect option is (b) because the reaction between sodium thiosulphate and iodine produces sodium tetrathionate, not sodium sulphate.

Key Concepts

Chemical Reactions

Chemical reactions occur when substances transform into new substances with different properties. It’s the foundation of chemistry. Reactions involve breaking and forming bonds between atoms. This process requires an understanding of reactants, products, and the conditions under which reactions occur.

• Reactants: The starting materials in a chemical reaction.
• Products: The substances formed as a result of the reaction.

One example of a common chemical reaction is the interaction between sodium thiosulphate and iodine.
In this particular reaction, iodine oxidizes sodium thiosulphate to produce sodium tetrathionate and sodium iodide, illustrating both the transformation of substances and the re-arrangement of atoms that characterize chemical reactions.

Ozonolysis

Ozonolysis is a specific type of chemical reaction used to study unsaturation in organic compounds. It is a highly effective method for cleaving double bonds in alkenes. When ozone is bubbled through a solution containing alkenes, it reacts with the double bonds according to the following pathway: the alkene undergoes ozonolysis to split into smaller molecules.
Why is Ozonolysis Important?

• Identifies the presence of unsaturation by cleaving carbon-carbon double bonds.
• The reaction provides structural insights by revealing the products formed after the cleavage.

This technique is not just used for analysis; it’s also practical in synthetic applications where controlled breakdown of complex molecules is desired, allowing for further chemical manipulations.

Oxidation

Oxidation is a key concept in both chemistry and everyday life. It involves the loss of electrons from a molecule, atom, or ion. This process is often associated with gaining oxygen or losing hydrogen. In the realm of chemical reactions, oxidation is crucial for forming new compounds.
Understanding Oxidation Reactions
In the case of sodium thiosulphate reacting with iodine, iodine acts as an oxidizing agent. It accepts electrons from sodium thiosulphate, undergoing a reduction itself while oxidizing sodium thiosulphate to form sodium tetrathionate.

• This demonstrates the principle of redox reactions, where oxidation and reduction occur simultaneously.

Redox reactions are central to many chemical processes, including energy production in batteries and metabolic reactions in the body.

Solubility

Solubility refers to a substance's ability to dissolve in a solvent, like water. It’s an essential property that influences how substances mix and react with each other.
Key Aspects of Solubility

• Saturability: How much solute can dissolve until a solution becomes saturated.
• Temperature: Generally, solubility of solids in liquids increases with temperature.
• Nature of the solute and solvent: "Like dissolves like"—polar solutes dissolve in polar solvents, while non-polar solutes dissolve in non-polar solvents.

In the specific case of sodium thiosulphate, it is quite soluble in water, making it easy to work with in various chemical experiments. Understanding solubility helps predict reaction outcomes and is critical for tasks like purification and formulation in pharmaceuticals.