Qualitative Analysis - Result Question 75
####78. When $16.8 g$ of white solid, $X$ were heated, $4.4 g$ of acid gas $A$, that turned lime water milky was driven off together with $1.8 g$ of a gas $B$ which condensed to a colourless liquid.
The solid that remained, $Y$, dissolved in water to give an alkaline solution, which with excess barium chloride solution gave a white precipitate $Z$. The precipitate effervesces with acid giving of carbon dioxide. Identify $A, B$ and $Y$ and write down the equation for the thermal decomposition of $X$.
$(1984,4 M)$
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Solution:
- $(X)$ is $NaHCO _3(M=84)$. The reactions involved are :
$$ \begin{array}{ccccc} & 2 NaHCO _3 & Na _2 CO _3(s)+CO _2(g)+H _2 O(g) \\ & Y & Y & A & B \\ & 168 g & 106 g & 44 g & 18 g \\ \Rightarrow & 16.8 g & 10.6 g & 4.4 g & 1.8 g \\ CO _2+Ca(OH) _2 \longrightarrow CaCO _3 \downarrow+H _2 O & & \end{array} $$
$H _2 O(g)$ is condensed to liquid water.
$$ \begin{gathered} Na _2 CO _3+BaCl _2 \longrightarrow BaCO _3+2 NaCl \\ Y \\ BaCO _3+2 HCl \longrightarrow BaCl _2+H _2 O+CO _2 \\ Z \end{gathered} $$
