Question

Which statement is not truc for alum? (1) Its cmpirical formula is \(\mathrm{K} \Lambda \mathrm{l}\left(\mathrm{SO}_{4}\right)_{2} \cdot 12 \mathrm{II}_{2} \mathrm{O}\). (2) Its aqucous solution is basic in nature. (3) It is uscd in dycing industrics. (4) On heating, it melts and swclls because of the loss of water of crystallization.

Short answer

Option 2 is not true; alum's aqueous solution is acidic.

Step-by-step solution

Analyze Option 1

Check if the given empirical formula, \(\text{K} \text{Al}\text{(SO}_4\text{)})_2 \text{. 12 H}_2\text{O}\), is correct for alum. This formula is consistent with the chemical composition of potash alum.

Analyze Option 2

Investigate if an aqueous solution of alum is basic. Alum solutions are typically acidic in nature, not basic.

Analyze Option 3

Evaluate if alum is used in dyeing industries. Alum is indeed used in dyeing processes to fix dyes onto fabrics.

Analyze Option 4

Determine if alum melts and swells on heating due to the loss of water of crystallization. This statement is true for alum.

Conclusion

Summarize the findings from the previous steps. The only incorrect statement is that alum's aqueous solution is basic.

Key concepts

Empirical Formula

The empirical formula of a compound is a simple representation of its composition in terms of the simplest whole-number ratio of atoms of each element present. For alum, its empirical formula is given as \(\text{K}\text{Al}\text{(SO}_4\text{)}_2 \text{. 12H}_2\text{O}\). This formula indicates that in each molecule of alum, there is one potassium ion (\(\text{K}^{+}\)), one aluminum ion (\(\text{Al}^{3+}\)), and two sulfate ions (\(\text{SO}_4^{2-}\)), along with twelve water molecules. Water of crystallization (the 12 \text{H}_2\text{O}\ part) is crucial because it stabilizes the structure of the solid alum.

Acidic Solution

When alum is dissolved in water, it creates an acidic solution. This is because alum contains sulfates, which can release \(\text{H}^+\) ions when dissolved. The acidity of alum solutions is opposite to the nature of basic solutions, which have \(\text{OH}^-\) ions. Given this property, alum is often involved in processes requiring acidic conditions.

Dyeing Industry

Alum plays a significant role in the dyeing industry. It is used as a mordant, a substance that fixes dyes onto fabrics. This process involves soaking the fabric in an alum solution, which helps the dye attach more effectively to the textile fibers. Here's why alum is so valuable in dyeing:

• Fixation: It helps dyes adhere better to the fabric.
• Color clarity: It enhances the vibrancy and sharpness of colors.

This makes alum indispensable in textile manufacturing and fabric arts.

Water of Crystallization

The term 'water of crystallization' refers to water molecules that are incorporated into the crystal structure of a compound. In the case of alum, these are the twelve water molecules (\(12 \text{H}_2\text{O}\)) part of its chemical formula. These water molecules are essential for maintaining the integrity of the crystalline solid. When alum is heated, it loses this water of crystallization, which results in melting and swelling. Understanding the role of water of crystallization helps in various applications, particularly in predicting and controlling the behavior of substances under different conditions.