Permanent hardness of water cannot be removed by:

A. Washing soda

B. Permutit method

C. Ion exchange method

D. Boiling

To address the question regarding the permanent hardness of water, we need to first understand what permanent hardness is and how it differs from temporary hardness. Permanent hardness is primarily caused by the presence of dissolved minerals, particularly calcium and magnesium sulfates or chlorides, which do not precipitate out of water upon boiling. This is in contrast to temporary hardness, which is mainly due to bicarbonates that can be removed by boiling the water.

Understanding Permanent Hardness

Permanent hardness is a characteristic of water that makes it unsuitable for certain applications, such as in boilers or for washing, because it leads to scale formation and reduces the effectiveness of soaps. The key point here is that boiling water does not remove the minerals responsible for permanent hardness.

Methods to Remove Hardness

Now, let’s look at the options provided:

• A. Washing soda: This method can effectively remove both temporary and some aspects of permanent hardness by precipitating calcium and magnesium ions as insoluble carbonates.
• B. Permutit method: This involves using a synthetic zeolite that exchanges sodium ions for calcium and magnesium ions, effectively softening the water.
• C. Ion exchange method: Similar to the permutit method, this process uses ion exchange resins to replace hardness ions with sodium ions, making the water softer.
• D. Boiling: This method is effective for temporary hardness but does not affect permanent hardness, as the minerals remain dissolved in the water.

Identifying the Correct Answer

Given the explanations of each method, it becomes clear that the correct answer to the question is D. Boiling. Boiling does not remove the dissolved minerals that cause permanent hardness, making it ineffective for this type of water hardness.

Real-World Implications

In practical terms, if you were to boil hard water, you might notice that while some of the temporary hardness is alleviated, the permanent hardness remains unchanged. This is why households with hard water often resort to water softening systems that utilize washing soda, permutit, or ion exchange methods to ensure their water is suitable for daily use.

In summary, while there are effective methods to treat hard water, boiling is not one of them when it comes to addressing permanent hardness. Understanding these differences is crucial for selecting the right approach to water treatment.