Question

(a) Describe how washing soda is produced starting from sodium chloride (common salt). Write equations of all the reactions involved.
(b) State whether an aqueous solution of washing soda is acidic or alkaline. Give reason for your answer.
(c) What is meant by saying that washing soda has detergent properties?
(d) Give two important uses of washing soda (or sodium carbonate).

Answer 1

The chemical name of washing soda is sodium carbonate and its chemical formula is $N{a_2}C{O_3}$ . It binds to the minerals like magnesium and calcium which leads to the hardness of water and therefore it helps the detergent to absorb into fibers properly in order to clean clothes. Hence, it is widely used in the laundry rooms for cleaning purposes.

Complete answer:
(a) The preparation of washing soda from sodium chloride takes place in following steps:
Step-1: Sodium chloride in its cold and concentrated solution i.e., brine is reacted with carbon dioxide, water and ammonia to give sodium hydrogen carbonate and ammonium chloride. The reaction proceeds as follows:
$NaCl + N{H_3} + {H_2}O + C{O_2} \to NaHC{O_3} + N{H_4}Cl$
Step-2: As sodium hydrogen carbonate formed is sparingly soluble in water, so its precipitate is extracted by filtration and dried. On heating sodium hydrogen carbonate, it decomposes to sodium carbonate along with the removal of carbon dioxide and water. The reaction proceeds as follows:
$2NaHC{O_3}\xrightarrow{{Heat}}N{a_2}C{O_3} + C{O_2} + {H_2}O$
Step-3: Anhydrous sodium carbonate is crystallized with ten moles of water molecules to form the washing soda which contains 10 molecules of water of crystallisation. The reaction proceeds as follows:
$N{a_2}C{O_3} + 10{H_2}O \to N{a_2}C{O_3} \cdot 10{H_2}O$
(b) The aqueous solution of washing soda is highly alkaline in nature because it is a salt of strong base i.e., sodium hydroxide ( $NaOH$ ) and a weak acid i.e., carbonic acid which results in the formation of alkaline solution. The pH level of washing soda is $11$ and it is quite caustic due to the high level of pH. So, it should not be touched with bare skin.
(c) Due to the high alkaline nature of washing soda, it is used for cleaning of clothes because it has a tendency to bind with minerals present in hard water and lift the impure particle in water and therefore help detergents to quickly clean the clothes. Due to its cleaning properties, it is widely used in laundry for deep cleaning and degreasing purposes.
(d) Two important uses of washing soda i.e., sodium carbonate are as follows:
1. It is used for removing permanent hardness of water.
2. It is widely used as a cleansing agent in domestic as well as industrial sectors.

Note:
It is important to note that washing soda is slightly different from soda ash. Soda ash is the anhydrous form of sodium carbonate whereas the washing soda consists of water molecules in it. Also, do not get confused with the terms washing soda and baking soda as these both terms are different. Washing soda consists of sodium carbonate whereas baking soda is another term for sodium bicarbonate i.e., $NaHC{O_3}$ .