No explanation is given for this question. Let's discuss the answer together.
72.
A metal salt solution forms a yellow precipitate with potassium chromate in acetic acid, a white precipitate with dilute sulphuric acid but does not give precipitate with sodium chloride or iodide. The white precipitate obtained when sodium carbonate is added to the metal salt solution will consist of
$$Pb$$ and $$Ba$$ both give yellow $$ppt.$$ with $${K_2}Cr{O_4}$$ in acetic acid and white precipitate with $$dil.\,{H_2}S{O_4}.$$ But lead salts give precipitate with sodium chloride or iodide whereas barium does not. It means given salt is barium salts and with sodium carbonate it gives white precipitate of barium carbonate.
73.
When chlorine is passed over dry slaked lime at room temperature, the main reaction product is
When chlorine gas is passed over dry slaked lime, it form bleaching powder i.e. $$CaOC{l_2}.$$
$$Ca{\left( {OH} \right)_2} + C{l_2} \to CaOC{l_2} + {H_2}O$$
74.
Which nitrate will decompose to give $$N{O_2}$$ on heating?
Only $$LiN{O_3}$$ gives $$N{O_2}$$ on heating. All other nitrates give oxygen.
\[\begin{align}
& 4LiN{{O}_{3}}\xrightarrow{\Delta }2L{{i}_{2}}O+4N{{O}_{2}}+{{O}_{2}} \\
& 2NaN{{O}_{3}}\xrightarrow{\Delta }2NaN{{O}_{2}}+{{O}_{2}} \\
\end{align}\]
75.
Amphoteric hydroxides react with both alkalies and acids. Which of the following group 2 metal hydroxides is soluble in sodium hydroxide?
No explanation is given for this question. Let's discuss the answer together.
78.
Which is incorrect statement ?
A
The heats of hydration of the dipositive alkaline earth metal decrease with an increase in their ionic size
B
$$NaN{O_3}$$ forms $$N{a_2}{O_2}$$ on heating
C
Hydration of alkali metal ion is less than that of $$IIA$$ group
D
Alkaline earth metal ions, because of their much larger charge to size ratio, exert a much stronger electrostatic attraction on the oxygen of water molecule surrounding them
Answer :
$$NaN{O_3}$$ forms $$N{a_2}{O_2}$$ on heating
$$\eqalign{
& {\text{Generally the ratio is kept as :}} \cr
& \frac{{\% \,{\text{Silica}}}}{{\% \,A{l_2}{O_3}}} = 2.5 - 4.0 \cr} $$
80.
The following compounds have been arranged in order of their increasing thermal stabilities. Identify the correct order.
$${K_2}C{O_3}\left( {\text{i}} \right)\,\,MgC{O_3}\left( {{\text{ii}}} \right)$$ $$CaC{O_3}\left( {{\text{iii}}} \right)\,\,BeC{O_3}\left( {{\text{iv}}} \right)$$