Permanent hardness of water cannot be removed by which one of the following methods?
[amp_mcq option1=”Treatment with washing soda” option2=”Calgon’s method” option3=”Boiling” option4=”Ion exchange method” correct=”option3″]
This question was previously asked in
UPSC NDA-2 – 2018
Permanent hardness of water is caused by the presence of dissolved sulfates and chlorides of calcium and magnesium. Boiling only removes temporary hardness, which is caused by dissolved bicarbonates of calcium and magnesium (these decompose upon heating to form insoluble carbonates). Methods like treatment with washing soda (sodium carbonate), Calgon’s method (using sodium hexametaphosphate), and the ion exchange method (using resins or zeolites) are effective in removing permanent hardness by precipitating or exchanging the dissolved calcium and magnesium ions. Therefore, boiling cannot remove permanent hardness.
This question distinguishes between temporary and permanent hardness of water and tests the knowledge of common methods used to remove water hardness.