Question

What is the difference between hard water and heavy water? Explain.

Answer 1

Hard water:

• The water which does not readily form lather with soap is called as Hard water.
• The hardness of the water is due to the presence of bicarbonates, Chlorides, and Sulfates of Calcium($\mathrm{Ca}$) and Magnesium($\mathrm{Mg}$).
• There are two types of the hardness of water: Temporary hardness and Permanent hardness.
• Temporary hardness is when water contains only bicarbonates of Calcium and Magnesium, which could easily be removed just by boiling.

$\underset{(\mathrm{Calcium}\mathrm{hydrogen}\mathrm{carbonate})}{\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{aq}\right)}\stackrel{\mathrm{boilng}}{\to }\underset{(\mathrm{Calcium}\mathrm{carbonate})}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)\downarrow }+\underset{\left(\mathrm{Water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{(\mathrm{Carbon}\mathrm{dioxide})}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$.

• But when water contains Sulphides and Chlorides of Magnesium and Calcium it is called permanent hard water.
• Permanent water can not be removed just by boiling. Washing soda is used to remove permanent hardness.

Heavy water:

• A compound that is made up of Oxygen and Deuterium (a heavier isotope of Hydrogen, which is denoted by D).
• The chemical formula of heavy water is ${\mathrm{D}}_2\mathrm{O}.$
• It has slightly different physical and chemical properties than regular water.
• It is used in NMR (nuclear magnetic resonance) and infrared spectroscopy.