Hydrogen and its Compounds (Non-metals)

Heavy water (D₂​O) is chemically similar to ordinary water ($\text{H₂}\text{O}$), but the hydrogen atoms are replaced by deuterium, which is an isotope of hydrogen with one proton and one neutron.

Molecular weight of ordinary water ($\text{H₂}\text{O}$): (2 $\times$ Atomic weight of H) + (1 $\times$ Atomic weight of O) = (2 $\times$ 1) + 16 = 18.

Molecular weight of heavy water (D​₂O): (2 $\times$ Atomic weight of D) + (1 $\times$ Atomic weight of O) = (2 $\times$ 2) + 16 = 4 + 16 = 20.

When hard water is boiled at home or in industries, it leaves deposits of calcium and magnesium salts. These deposits reduce the efficiency of boilers, kettles and pipes and can cause blockages and even burst of the boilers.

If salt level increases in irrigation water it becomes harder for lawns and landscape plant to take up water even though the soil is moist. Hard water blocks Xylem tissues of the plants and thus not suitable for irrigation

Permanent hardness is caused by the presence of dissolved chlorides and sulfates of calcium (CaCl₂​, CaSO₄​) and magnesium ($\text{MgCl₂}$, $\text{MgSO₄}$). This type of hardness cannot be removed by boiling.

Temporary hardness, on the other hand, is caused by bicarbonates of calcium and magnesium, which can be removed by boiling.

The pH value of pure water is 7. Pure water is neutral by nature. The solution with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline.