Why is alum added to water containing suspended impurities ?

Options

A. To make a colloidal solution
B. To coagulate the suspended impurities
C. To remove impurities of calcium and magnesium
D. To protect the colloidal solution from getting precipitated

Explanation

**Step-by-Step Solution:**

1. **Understanding Colloidal Solutions**:
- Colloidal solutions are mixtures where tiny particles are dispersed throughout a continuous medium (like water). These particles can be suspended and often carry a charge.

2. **Presence of Suspended Impurities**:
- In many cases, these colloidal solutions contain suspended impurities that can affect the clarity and quality of the water.

3. **Role of Electrolytes**:
- To remove these impurities, we can use electrolytes. Electrolytes are substances that dissociate into ions when dissolved in water, and they can carry either a positive or negative charge.

4. **Introduction of Alum**:
- Alum, which is a type of electrolyte, contains ions such as K⁺ (potassium), Al³⁺ (aluminum), and SO₄²⁻ (sulfate). These ions can interact with the charged impurities in the colloidal solution.

5. **Neutralization of Charges**:
- When alum is added to the water, the charged ions from the alum will neutralize the charges on the suspended impurities. This neutralization is crucial because charged particles tend to repel each other, keeping them suspended.

6. **Coagulation Process**:
- Once the charges are neutralized, the suspended impurities can aggregate or coagulate together. This means they clump together and form larger particles.

7. **Precipitation of Impurities**:
- After coagulation, these larger particles are heavy enough to settle down or precipitate out of the solution, effectively removing them from the water.

8. **Resulting Purification**:
- As a result, the water becomes clearer and purer because the suspended impurities have been removed through this coagulation process facilitated by the alum.

**Conclusion**:
- Therefore, alum is added to water containing suspended impurities to coagulate and remove these impurities, leading to the purification of the water.

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