Which one of the following removes temporary hardness of water ?

Options

A. Slaked lime
B. Plaster of paris
C. `CaCO_(3)`
D. Hydrolith

Answer

To solve the question "Which one of the following removes temporary hardness of water?", we can follow these steps:

### Step 1: Understand Temporary Hardness
Temporary hardness of water is primarily caused by the presence of bicarbonates of calcium (Ca(HCO₃)₂) and magnesium (Mg(HCO₃)₂).

### Step 2: Identify the Types of Hardness
There are two types of hardness in water:
- **Temporary Hardness**: Caused by bicarbonates of calcium and magnesium.
- **Permanent Hardness**: Caused by sulfates and chlorides of calcium and magnesium.

### Step 3: Removal of Temporary Hardness
Temporary hardness can be removed through various methods, one of which is Clarke's process. This process involves boiling the water with slake lime (calcium hydroxide, Ca(OH)₂).

### Step 4: Chemical Reactions Involved
When slake lime is added to water containing bicarbonates, the following reactions occur:
1. Calcium bicarbonate reacts with slake lime:
\[ Ca(HCO₃)₂ + Ca(OH)₂ \rightarrow 2CaCO₃ + 2H₂O \]
This produces calcium carbonate and water.

2. Magnesium bicarbonate reacts with slake lime:
\[ Mg(HCO₃)₂ + Ca(OH)₂ \rightarrow CaCO₃ + MgCO₃ + 2H₂O \]
This produces both calcium carbonate and magnesium carbonate along with water.

### Step 5: Conclusion
From the above information, we conclude that slake lime (calcium hydroxide) is the substance that removes temporary hardness of water.

### Final Answer
The correct option is **slake lime (calcium hydroxide)**.

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