Direction: In the following questions, a statement of Assertion (A) ...
Permanent hardness of water can be removed by using washing soda. Washing soda reacts with soluble calcium and magnesium chlorides and sulphates in hard water to form insoluble carbonates.
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Direction: In the following questions, a statement of Assertion (A) ...
**Explanation:**
**Assertion (A):** Permanent hardness of water is removed by treatment with washing soda.
**Reason (R):** Washing soda reacts with soluble magnesium and calcium sulphate to form insoluble carbonates.
The correct answer is option 'A', which states that both the assertion (A) and the reason (R) are correct, and the reason (R) is the correct explanation of the assertion (A).
**Explanation:**
Permanent hardness of water is caused by the presence of soluble calcium and magnesium salts, primarily calcium sulfate (CaSO4) and magnesium sulfate (MgSO4). These salts do not precipitate when water is boiled, unlike temporary hardness caused by the presence of bicarbonates. Therefore, an alternative method is required to remove permanent hardness.
Washing soda, also known as sodium carbonate (Na2CO3), is commonly used to remove permanent hardness. When washing soda is added to hard water, it reacts with the soluble calcium and magnesium salts to form insoluble carbonates. This reaction can be represented as follows:
CaSO4 + Na2CO3 -> CaCO3 + Na2SO4
MgSO4 + Na2CO3 -> MgCO3 + Na2SO4
The formed calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) are insoluble and can be easily removed by precipitation or filtration. The remaining sodium sulfate (Na2SO4) remains in solution and does not contribute to water hardness.
Therefore, washing soda effectively removes permanent hardness by converting the soluble calcium and magnesium salts into insoluble carbonates. This process is known as precipitation or chemical softening.
Hence, both the assertion (A) and the reason (R) are correct, and the reason (R) provides the correct explanation for the assertion (A).
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