Question

Name the compound which is obtained from baking soda and is used to remove permanent hardness of water.

Answer 1

Baking soda is chemically Sodium bicarbonate having the chemical formula $NaHC{O_3}$. Hard water is the type of water which contains Calcium, and Magnesium ions which requires more soaps than normal to form lather.

Complete step by step answer:
(1) Hard water is a category of water, and it is due to the presence of Calcium, and Magnesium ions in water. Soaps are the Sodium or Potassium salts of fatty acids which means that they contain Sodium or Potassium ions. These ions are replaced by the Calcium, and Magnesium ions of the hard water when treated to form an insoluble substance called the scum.
(2) In hard water more soaps are needed to form lather which will increase the cost of washing. So, some substances are added to the hard water which can stop the Calcium, and Magnesium ions from forming the scum.
(3) Sodium bicarbonate or baking soda when heated yields carbon dioxide, water, and dry Sodium carbonate which is called the soda ash. This sodium carbonate can react with water to form sodium decahydrate which has chemical formula $N{a_2}C{O_3} \cdot 10{H_2}O$.
(4) This washing soda or Sodium carbonate is used to remove the permanent hardness of water because carbonate ions react with the free Calcium, and Magnesium ions of hard water to form the precipitate Calcium carbonate, and Magnesium carbonate. The reaction is as follows:
Calcium ions + Sodium carbonate $\to$ Calcium carbonate + Sodium ions
$C{a^{2 + }}({\text{aq)}} + N{a_2}C{O_3}({\text{aq)}} \to CaC{O_3}({\text{ppt)}} + 2N{a^ + }({\text{aq)}}$
After treating with Sodium carbonate, the water becomes soft due to the absence of Calcium, and Magnesium ions which are used up in the above precipitate formation.
Hence, Sodium carbonate obtained from baking soda is used to remove the permanent hardness of water.

Note:
Sometimes Calcium carbonate, and Magnesium carbonate undergo precipitation reaction to form limescale which accumulates on the metal taps and breaks them with time, so, Sodium carbonate is not used in treating tap hard water, instead ion exchange columns are used.