Substances in Common Use — Science STD 9 — Question
Maharashtra BoardEnglish MediumSTD 9ScienceSubstances in Common Use2 Marks
Question
Sodium carbonate is added to hard water to make it soft.
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Answer
The hardness of water is due to the presence of chlorides and sulphates of calcium and magnesium in it.
$Na _2 CO _3$ is added to it to soften such water and make it suitable for use.
The reaction with $Na _2 CO _3$ causes the formation of insoluble carbonate salts of magnesium and calcium thus making the water soft.
$MgCl _{2(a q)}+ Na _2 CO _{3(s)} \rightarrow MgCO _{3(s)}+2 NaCl _{( s )}$
Magnesium Sodium Magnesium Sodium
chloride carbonate carbonate chloride
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