Permanenet hardness of water is removed by adding

Options

A. Sodium bicarbonate
B. Washing soda
C. Calcium hydroxide
D. Sodium chloride

Answer

To solve the question regarding how to remove permanent hardness of water, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Hardness**:
- Water hardness is classified into two types: temporary hardness and permanent hardness.
- Temporary hardness is primarily due to the presence of calcium and magnesium bicarbonates, which can be removed by boiling.
- Permanent hardness, on the other hand, is caused by calcium and magnesium sulfates and chlorides, which cannot be removed by boiling.

2. **Identify the Method to Remove Permanent Hardness**:
- Since permanent hardness cannot be removed by boiling, we need to use a chemical method.
- The most common method to remove permanent hardness is by using washing soda (sodium carbonate, Na2CO3).

3. **Chemical Reaction**:
- The reaction between washing soda and the hardness-causing salts can be represented as follows:
\[ \text{CaCl}_2 + \text{Na}_2\text{CO}_3 \rightarrow \text{CaCO}_3 \downarrow + 2\text{NaCl} \]
- In this reaction, calcium chloride (CaCl2) reacts with sodium carbonate (Na2CO3) to form calcium carbonate (CaCO3), which precipitates out of the solution, and sodium chloride (NaCl) remains dissolved.

4. **Precipitation and Removal**:
- The precipitated calcium carbonate (CaCO3) can be easily removed from the water by filtration or sedimentation.
- This process effectively reduces the permanent hardness of the water.

5. **Conclusion**:
- Therefore, the permanent hardness of water is removed by adding washing soda (sodium carbonate).

### Final Answer:
Permanent hardness of water is removed by adding washing soda (sodium carbonate).

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