Polyphosphates llike sodium hexametaphosphate (calgon) are used as water softening agents because they

Options

A. form soluble complexes with anionic species
B. precipitate anionic species
C. form soluble complexes with cationic species
D. precipitate cationic species.

Explanation

**Step-by-Step Solution:**

1. **Understanding Hard Water**: Hard water contains high concentrations of cations, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions can cause scaling and reduce the effectiveness of soaps and detergents.

2. **Introduction to Polyphosphates**: Polyphosphates, such as sodium hexametaphosphate (commonly known as Calgon), are chemical compounds that can interact with cations in water.

3. **Mechanism of Action**: Sodium hexametaphosphate works by forming soluble complexes with the cations present in hard water. When it is added to hard water, it reacts with the calcium and magnesium ions.

4. **Chemical Reaction**: The general reaction can be represented as:
\[ \text{Na}_2\text{Al}_2\text{Si}_2\text{O}_8 \cdot x\text{H}_2\text{O} + \text{Ca}^{2+} \text{ or } \text{Mg}^{2+} \rightarrow \text{Ca} \text{ or } \text{Mg} \cdot \text{Al}_2\text{Si}_2\text{O}_8 + 2\text{Na}^+ \]
In this reaction, the sodium ions (Na⁺) replace the calcium or magnesium ions, effectively softening the water.

5. **Conclusion**: The reason polyphosphates like sodium hexametaphosphate are used as water softening agents is that they form soluble complexes with cationic species (the calcium and magnesium ions), which prevents these ions from causing hardness in the water.

6. **Final Answer**: Therefore, the correct option is that polyphosphates form soluble complexes with cationic species.

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