Question

A hydrated solid X on heating initially gives a monohydrated compound Y. Y upon heating above 373 K leads to an anhydrous white powder Z. X and Z, respectively, are:

a.) washing soda and soda ash
b.) washing soda and dead burnt plaster
c.) baking soda and dead burnt plaster
d.) baking soda and soda ash

Answer 1

. Hydrates are the inorganic salts which have water molecules combined with them in different ratios as an integral part of the crystal. These hydrates are either bound to a metal center or crystallized with the metal complex.

Complete step by step answer:
Given in the question that:
A hydrated solid X on heating initially gives a monohydrated compound Y and Y upon heating above 373 K leads to an anhydrous white powder Z.
Washing soda is sodium carbonate. It is an inorganic compound and its formulae varies for its hydrates. But all the forms of washing soda are white and they are water soluble. The compound X is washing soda.
When washing soda is heated it loses its water of crystallization and forms soda ash. This is a two-step process, washing soda has 10 water molecules of crystallization so when it is heated first it loses 9 water molecule of crystallization and when it is heated above 373 K leads to lose of the last water molecule of crystallization and formation of an anhydrous white powder which is soda ash.
The reaction involved is shown below:

$\underset{\underset{(X)}{\mathop{washing\text{ }soda}}\,}{\mathop{N{{a}_{2}}C{{O}_{3}}.10{{H}_{2}}O}}\,(s)\xrightarrow{\Delta }\underset{(Y)}{\mathop{N{{a}_{2}}C{{O}_{3}}.{{H}_{2}}O}}\,\xrightarrow[T>373K]{\Delta }\underset{\underset{(Z)}{\mathop{Soda ash}}\,}{\mathop{N{{a}_{2}}C{{O}_{3}}}}\,$
So, the correct answer is “Option A”.

Note: Sodium carbonate is obtained as three hydrates and one anhydrous salt. Here the term anhydrous means that the compounds in which water molecules are involved. The three hydrates of sodium carbonate are sodium carbonate decahydrate, sodium carbonate heptahydrate, and sodium carbonate monohydrate, where deca, mono and hepta are the number of water molecules of crystallization present in the compound.