Question

The number of molecules of water of crystallization present in washing soda crystals is:
A.Five
B.Two
C.Ten
D.Seven

Answer 1

To answer this question, you should recall the concept of preparation of washing soda. Washing soda is a cleansing agent and is used in households, industries and laboratories as it is an essential component in most detergents for powder, liquid, or single pod formulas.

Complete step by step answer:
The chemical name of washing Soda is hydrated sodium carbonate. The formula can be written as $\;N{a_2}C{O_3}.10{H_2}O\;$. The sodium carbonate overcomes the hardness due to presence of impurities and softens water making it favourable for the cleaning ingredients, lifts soil from the fabrics and suspends the soil in the wash water. The process of preparation is known as Solvay’s process. The steps involved in the preparation of washing soda are:

Purification of Brine	Brine refers to a saturated solution of salt obtained by evaporation with the removal of impurities like calcium, magnesium etc. by the precipitation process. This solution prepared undergoes filtration and is mixed with ammonia in the ammonia tower and the ammonia tower gets cooled.
Formation of sodium hydrogen carbonate	Carbon dioxide is passed through an ammoniated brine solution:$N{H_3}\left( {aq} \right)\; + \;C{O_2}\left( g \right)\; + \;NaCl\left( {aq} \right)\; + {H_2}O\; \to \;NaHC{O_3}\left( s \right)\; + \;N{H_4}Cl\left( {aq} \right)$
Formation of sodium carbonate	Sodium Bicarbonate is heated at a temperature of $300^\circ C.$Hence, formations of sodium carbonate take place: $2NaHC{O_{3\;}} \to \;N{a_2}C{O_3}\; + \;C{O_2}\; + \;{H_2}O$
Recovery of ammonia	Ammonia can be recovered by treating the solution of $N{H_4}Cl$with$Ca{\text{ }}{\left( {OH} \right)_2}$. This ammonia is again used in the Solvay process and$CaC{l_2}$ is obtained as a by-product: $2N{H_4}Cl\; + \;Ca{\left( {OH} \right)_{2\;}} \to \;2N{H_3}\; + \;CaC{l_2}\; + \;{H_2}O$

Hence, the correct option is option C, i.e. ten.

Note:
Physical properties and chemical properties of sodium carbonate:Physical features include crystalline nature and white colour It exists in many types: monohydrated salt$\left( {N{a_2}C{O_3}.10{H_2}O} \right)$, anhydrous salt$\left( {N{a_2}C{O_3}} \right)$, heptahydrate salt $\left( {N{a_2}C{O_3}.7{H_2}O} \right)$and decahydrate salt $\left( {N{a_2}C{O_3}.10{H_2}O} \right).$It has a melting point of$851^\circ C$.In the prolonged exposure to heat and temperature, it loses its water to form an anhydrous salt which is known as soda ash: $N{a_2}C{O_3}.10{H_2}O\; \to \;N{a_2}C{O_3}.{H_2}O\; \to \;N{a_2}C{O_3}\;\left( {at{\text{ }}373{\text{ }}K} \right)$