Question

A white solid X on heating gives a white solid Y and an acidic gas Z. Gas Z is also given out when X reacts with an acid. The compound Y is also formed if caustic soda is left open in the atmosphere. X, Y and Z are:
(A)X - $NaHC{O_3}$, Y - $N{a_2}C{O_3}$, Z - $C{O_2}$
(B)X - $N{a_2}C{O_3}$, Y – NaOH, Z - $C{O_2}$
(C)X - $NaHC{O_3}$, Y - $NaHC{O_3}$, Z - $C{O_2}$
(D)X – NaOH, Y - $NaHC{O_3}$, Z - $C{O_2}$

Answer 1

Z in all options is the same so you already know what Z is. Then check what is formed when caustic soda is left open in the atmosphere, this will ultimately lead you to X. Compound X is used in cooking and Y is the main component of washing soda.

Complete step by step answer:
-The reaction in terms of X, Y and Z is as follows:
$X\xrightarrow{\Delta }Y + Z$
-Since in all the options Z is given as $C{O_2}$ and it is an acidic gas, we can say that: Z is $C{O_2}$.
-It is given in the question that compound Y is formed if caustic soda is left open in the atmosphere. So, first let us check what Y is.
Caustic soda is another name for sodium hydroxide (NaOH). When it is left open in the atmosphere it reacts with carbon dioxide ($C{O_2}$) and forms sodium carbonate ($N{a_2}C{O_3}$). This reaction is:
$2NaOH + C{O_2} \to N{a_2}C{O_3} + {H_2}O$
So, Y will be sodium carbonate ($N{a_2}C{O_3}$).
-Now we have both the products Y and Z, so what we just need to find now is that what on heating produces $N{a_2}C{O_3}$ and $C{O_2}$also confirm if that same compound produces $C{O_2}$ when reacted with acid.

We all know that when sodium bicarbonate is heated it produces both sodium carbonate and carbon dioxide. The reaction is:
$2NaHC{O_3}\xrightarrow{\Delta }N{a_2}C{O_3} + C{O_2} + {H_2}O$
Also when sodium bicarbonate reacts with acid HCl it forms NaCl along with $C{O_2}$. The reaction is:
$NaHC{O_3} + HCl \to NaCl + C{O_2} + {H_2}O$
So, now we can say that X is $NaHC{O_3}$.
So, the correct option is: (A) X - $NaHC{O_3}$, Y - $N{a_2}C{O_3}$, Z - $C{O_2}$.

Note: Don’t get confused between caustic soda and baking soda. Both are different. Caustic soda is sodium hydroxide (NaOH) while baking soda is sodium bicarbonate ($NaHC{O_3}$). Baking also helps regulate the pH.