Polyphosphates are used as water softening agents because they

Options

A. Form solube complexes with anionic species
B. Precipitate anionic species
C. Form soluble complexes with cationic species
D. Precipitate cationic species

Explanation

To solve the question about why polyphosphates are used as water softening agents, we will follow these steps:

### Step 1: Understand the Problem
The question asks why polyphosphates are utilized as water softening agents. We need to analyze the options provided to identify the correct reason.

### Step 2: Analyze the Options
The options given are:
1. Form soluble complexes with anionic species
2. Precipitate anionic species
3. Form soluble complexes with cationic species
4. Precipitate cationic species

### Step 3: Identify the Role of Polyphosphates
Polyphosphates are known to interact with cations that contribute to water hardness, such as calcium (Ca²⁺) and magnesium (Mg²⁺).

### Step 4: Determine the Correct Option
From the analysis, we can conclude that polyphosphates form soluble complexes with cations. This means that they bind with the cations responsible for hardness in water, preventing them from precipitating out and thus softening the water.

### Step 5: Write the Reaction
For example, when polyphosphate (like sodium polyphosphate, Na₄P₂O₇) interacts with calcium ions (Ca²⁺), it forms a soluble complex. The reaction can be represented as:
\[ \text{Ca}^{2+} + \text{Na}_4\text{P}_2\text{O}_7 \rightarrow \text{Ca}(\text{P}_2\text{O}_7) + 2\text{Na}^+ \]

### Step 6: Conclusion
Based on the above reasoning, the correct answer is that polyphosphates are used as water softening agents because they **form soluble complexes with cationic species**.

### Final Answer
Polyphosphates are used as water softening agents because they form soluble complexes with cationic species.

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