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Surface Chemistry — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistrySurface Chemistry2 Marks
Question
Why do we add alum to purify water?
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Answer

River water carries negatively charged colloidal particles of clay and sand; alum $(K_2SO_4Al_2(SO_4)_324H_2O)$ is added to river water to coagulate the colloidal particles of clay and sand. Thus, alum helps to purify water.

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