Question

The incorrect statement is

• A. Lithium is the strongest reducing agent among the alkali metals.
• B. Lithium is least reactive with water among the alkali metals.
• C. $LiN{O}_3$ decomposes on heating to give $LiN{O}_2$ and $O_2$.
• D. $LiCl$ crystallise from aqueous solution as $LiCl.2H_{2}O$.

Answer 1

The correct option is C $LiN{O}_3$ decomposes on heating to give $LiN{O}_2$ and $O_2$.

1. Reducing character of alkali metal increase from Na to Cs due to decreasing ionisation potential. Lithium has more reducing power than sodium eventhough it has high ionisation energy. This is because of the high hydration energy of Lithium.
2. Lithium is least reactive with water among alkali due to its high ionisation energy.
3. $LiN{O}_3$(Lithium nitrate) on heating gives a mixture of $L{i}_{2}O,N{O}_{2}and{O}_2$.
$4LiN{O}_3\to 2L{i}_{2}O+4N{O}_2+O_2$
4. LiCl is deliquescent and crystallises as a hydrate, $LiCl.2H_{2}O$
Hence the incorrect statement is option (c).

Theory
Anomalous Properties of Lithium
The anomalous behaviour of lithium is due to:
The exceptionally small size of its atom and ion. The size of the Li atom is 152 pm and $L{i}^{+}$ is 76 pm.
High polarizing power (i.e., charge/radius ratio ). As a result, there is an increased covalent character in lithium compounds which is responsible for their solubility in organic solvents.
Li is much harder. So, its M.P. and B.P. are higher.
Li is the least reactive but the strongest reducing agent. On combustion in air, it forms mainly monoxide, $L{i}_{2}O$, and nitride, $L{i}_{3}N$
LiCl is deliquescent and crystallises as a hydrate, $LiCl.2H_{2}O$ whereas other alkali metal chlorides do not form hydrates.
Lithium hydrogen carbonate is not obtained in the solid form. All other elements form solid hydrogen carbonates.
Lithium forms no ethynide on reaction with ethyne. Other alkali metals form ethynide on reaction with ethyne.
Lithium nitrate when heated gives lithium oxide, $L{i}_{2}O$
$4LiN{O}_3\to 2L{i}_{2}O+4N{O}_2+O_2$
Other alkali metal nitrates decompose to give the corresponding nitrite.
$2NaN{O}_3\stackrel{{500}^{\circ }C}{\rightleftharpoons }2NaN{O}_2+O_2$
$2NaN{O}_2+2HCl\to 2NaCl+H_{2}O+N{O}_2+NO$
$2NO+O_2\to 2N{O}_2$
$4NaN{O}_2\stackrel{{800}^{\circ }C}{\rightleftharpoons }2N{a}_{2}O+5O_2+2N_2$
$N{a}_{2}C{O}_3+NO+N{O}_2\to 2NaN{O}_2+C{O}_2$
$LiF,L{i}_{2}O$ and $L{i}_{2}C{O}_3$ are comparatively much less soluble in water than the corresponding compounds of other alkali metals