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we know that Na is more reactive than Ca and Mg, then whyduring the formation of scum Na is displaced by Ca and Mg?

we know that Na is more reactive than Ca and Mg,
then whyduring the formation of scum Na is displaced by Ca and Mg?
 

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1 Answers

Bhavya
askIITians Faculty 1281 Points
6 years ago
Hard water is water containing high amounts of mineral ions. The most common ions found in hard water are the metal cationscalcium (Ca2+)and magnesium (Mg2+), though iron, aluminum, and manganese may also be found in certain areas. These metals are water soluble, meaning they will dissolve in water. The relativelyhigh concentrations of these ions can saturate the solution and consequently cause the equilibrium of these solutes to shift to the left, towards reactants.In other words,the ions can precipitate out of the solution. This displacement of minerals from the solution is responsible for the calcination often seen on water faucets, which is a precipitation of calcium or magnesium carbonate. Hard water may also react with other substances in the solution, such as soap,and form a precipitate called "scum."

So here Na is displacing Ca and Mg from hard water.

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