Which of the following statement is correct regarding hardness of water?
I. Hardness in water is caused by Ca²+ and Mg2+ ions
II. Hard water is suitable for bathing, washing and cleaning
Statement I is correct: Water hardness is primarily caused by the presence of multivalent metallic cations, most notably
calcium Ca2+ and magnesium Mg2+ ions.
Statement II is incorrect: Hard water is not suitable for bathing, washing, and cleaning. The calcium and magnesium ions react with soap to
form an insoluble, sticky precipitate known as soap scum. This prevents the soap from lathering easily, which wastes soap and leaves a
residue on skin, hair, and fabrics.
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