Problem 122 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: \(\begin{array}{ll}\text { List I } & \text { List II }\end{array}\) 1\. efflorescent (i) \(\mathrm{NaOH}\) 2\. deliquescent (ii) \(\mathrm{KOH}\) 3\. fusion mixture (iii) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{K}_{2} \mathrm{CO}_{3}\) 4\. washing soda (iv) \(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}\) The correct matching is 1 2 3 4 (a) (ii) (i) (iv) (iii) (b) (i) (ii) (iii) (iv) (c) (ii) (i) (iii) (iv) (d) (i) (iii) (iv) (ii)

Step-by-Step Solution

Answer

The correct option is (c): 1-(iv), 2-(ii), 3-(iii), 4-(i).

Step 1: Understanding Efflorescent

Efflorescent substances are those that lose water and form a powder when exposed to air. Sodium carbonate decahydrate \( \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} \), known as washing soda, is efflorescent.

Step 2: Understanding Deliquescent

Deliquescent substances absorb moisture from the air and dissolve in it, forming a solution. Sodium hydroxide \( \mathrm{NaOH} \) and potassium hydroxide \( \mathrm{KOH} \) are common deliquescent compounds.

Step 3: Identifying the Fusion Mixture

The fusion mixture is typically a mixture of sodium carbonate \( \mathrm{Na}_{2} \mathrm{CO}_{3} \) and potassium carbonate \( \mathrm{K}_{2} \mathrm{CO}_{3} \). This combination is used to dissolve less soluble oxides.

Step 4: Determining Washing Soda

Washing soda refers to sodium carbonate decahydrate \( \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} \), which is known for being efflorescent.

Step 5: Matching List I with List II

1. Efflorescent (iv), as \( \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} \) is efflorescent.2. Deliquescent (ii), because \( \mathrm{KOH} \) is deliquescent.3. Fusion mixture (iii), since \( \mathrm{Na}_{2} \mathrm{CO}_{3} \) and \( \mathrm{K}_{2} \mathrm{CO}_{3} \) form a fusion mixture.4. Washing soda (i), as \( \mathrm{NaOH} \) is not related and is incorrect, making option (a) a better fit.

Key Concepts

Efflorescent Substances

Efflorescent substances are unique in that they have the ability to lose water upon exposure to air, leading them to form a powdery crust on their surface. This process occurs because these substances contain water molecules in a crystalline structure, which can be released into the surrounding environment when humidity levels are lower than the compound's equilibrium humidity. An excellent example of an efflorescent substance is washing soda, or sodium carbonate decahydrate \( \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} \).

• Efflorescent substances are known for their moisture-losing properties.
• They often transform into a powder when exposed to the air.
• Their practical applications include their use in biological and chemical industries where controlled hydration is essential.

Deliquescent Compounds

Deliquescent compounds are the opposite of efflorescent substances. These compounds have a great affinity for water, so much so that they can absorb moisture from the air to the point where they dissolve and form an aqueous solution. This property makes them very useful for various industrial and laboratory applications.

Examples of deliquescent substances include sodium hydroxide \( \mathrm{NaOH} \) and potassium hydroxide \( \mathrm{KOH} \). Both are strong bases that tend to absorb moisture rapidly.

• Deliquescent substances are utilized as drying agents because of their ability to capture moisture.
• They are often stored in airtight containers to prevent them from absorbing too much moisture and forming unwanted solutions.
• Their hygroscopic nature is beneficial in specific chemical processes requiring the presence of moisture.

Fusion Mixture

Fusion mixtures are combinations of substances, usually salts, that are used to facilitate the dissolution of less soluble compounds by lowering their melting points when heated together. A typical example of a fusion mixture includes sodium carbonate \( \mathrm{Na}_{2} \mathrm{CO}_{3} \) and potassium carbonate \( \mathrm{K}_{2} \mathrm{CO}_{3} \). When these two compounds are used in combination, their melting point is lower than when each is used alone.

• Fusion mixtures aid in melting and dissolving otherwise difficult-to-dissolve substances.
• They are frequently used in analytical chemistry to ensure thorough mixing and reactions of solid reactants.
• This method benefits applications where uniform heating and melting are essential.

Washing Soda

Washing soda, scientifically known as sodium carbonate decahydrate \( \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} \), is indispensable in various cleaning applications. This compound functions effectively as a water softener by removing calcium and magnesium ions, which are responsible for water hardness.

Washing soda is an example of an efflorescent substance, meaning it can lose water upon exposure to the air, resulting in a powdered form.

• Washing soda is commonly used in laundry detergents for its ability to clean and soften water.
• It is also used in the manufacturing of glass and some chemicals.
• Despite its varying applications, careful storage is necessary to maintain its stability and effectiveness.