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Salts of oxoacids
Since the alkali metals are highly electropositive, therefore their hydroxides are very strong bases and hence they form salts with all oxoacids ( H2CO3, H3PO4, H2SO4, HNO3, HNO2 etc) . They are generally soluble in water and stable towards heat. The carbonates (M2CO3) of alkali metals are remarkably stable upto 1273 K, above which they first melt and then eventually decompose to form oxides. Li2CO3 , however is considerably less stable and decomposes readily.
Li2CO3 → Li2O + CO2
This is presumably due to large size difference between Li+ and CO2-3 which makes the crystal lattice unstable.
Being strongly basic, alkali metals also form solid bicarbonates. No other metals forms solid bicarbonates though NH4HCO3 also exists as a solid. Lithium, however does not form solid bicarbonate though it does exist in solution. All the bicarbonate on gentle heating undergo decomposition to form carbonates with the evolution of CO2.
2MHCO3 → M2CO3 + CO2 + H2O
All the carbonates and bicarbonates are soluble in water and their solubilities increase rapidly on descending the group. This is due to the reason that lattice energies decrease more rapidly than their hydration energies on moving down the group.
Complete and balance the following:
(i) LiNO3 ---→
(ii) NaNO3 ---→
(i) 4LiNO3 -----→ 2i2O + 4NO2 + O2
(ii) 2NaNO3 ----→ 2NaNO2 + O2
Which hydroxide is most basic?
Which of the following alkali metal halides has the lowest lattice energy?
(A) LiF (B) NaCl