Answer:
Solubility: (i) Nitrates,
carbonates and sulphates of alkali metals are soluble in water. The solubility increases
as we move down the group as lattice energies decrease more rapidly than
hydration energies due to increase in the sizes of metal ions.
(ii) Nitrates of
alkaline earth metals are also soluble in water. Their solubility decreases as
we move down the group as hydration energies decrease more rapidly than the
lattice energies.
The
sulphates of Be and Mg are soluble in water. The solubility of carbonates and
sulphates of alkaline earth metals decrease down the group as hydration
energies decrease and lattice energies remain nearly the same down the group as
the sizes of\[CO_{3}^{2-}\]and \[SO_{4}^{2-}\]anions are much larger than
cations.
Thermal
stability: (i) Except\[LiN{{O}_{3}}\], all other alkali metal nitrates decompose
into corresponding nitrites and \[{{O}_{2}}\].
\[2MN{{O}_{3}}\to
2MN{{O}_{2}}+{{O}_{2}}(M=Na,K,Rb,Cs)\]
\[LiN{{O}_{3}}\]and
all the alkaline earth metal nitrates decompose to form corresponding oxides, \[N{{O}_{2}}\]and\[{{O}_{2}}.\]
\[2M{{(N{{O}_{3}})}_{2}}\to
2MO+2N{{O}_{2}}+{{O}_{2}}\]\[(M=Be,Mg,Ca,Sr,orBa)\]
\[4LiN{{O}_{3}}\to
2L{{i}_{2}}O+2N{{O}_{2}}+{{O}_{2}}\]
(ii) Except\[L{{i}_{2}}C{{O}_{3}}\],
all other alkali metal carbonates are thermally stable. \[L{{i}_{2}}C{{O}_{3}}\]decomposes
on heating.
\[L{{i}_{2}}C{{O}_{3}}\to
L{{i}_{2}}O+C{{O}_{2}}.\]
Carbonates of
alkaline earth metals decompose on heating into corresponding oxides and\[C{{O}_{2}}\].
Their decomposition temperatures increase gradually from \[BeC{{O}_{3}}\] to\[BeC{{O}_{3}}\].
\[MC{{O}_{3}}\to MO+C{{O}_{2}}\]
Except \[L{{i}_{2}}S{{O}_{4}}\],
all other alkali metal sulphates are thermally stable. \[L{{i}_{2}}S{{O}_{4}}\]decomposes
on heating.
\[L{{i}_{2}}S{{O}_{4}}\to L{{i}_{2}}O+S{{O}_{3}}\]
Sulphates of
alkaline earth metals decompose on heating giving the corresponding oxide and \[S{{O}_{3}}\]
\[MS{{O}_{4}}\to
MO+S{{O}_{3}}\]
The decomposition
temperatures increase gradually on moving down the group.
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