Question

Which alkali metal forms bicarbonate only in aqueous solution?

Answer 1

The given question is that which alkali metal forms bicarbonate only in aqueous solution.

• All alkali metals form bicarbonates except lithium metal.
• LiHCO3 is a mixed compound comprises of Hydrogen, Oxygen, Carbon and lithium.
• It's name is Lithium bicarbonate.
• It cannot exist in a form of solid.
• The hydrating energy of lithium is extremely high.
• It is more stable in the form of an aqueous solution than in the solid form
• The solids like Na (sodium), k(potassium), Rb(Rubidium) , Fr(Francium), Cs(cesium).
• The above metals form solid bicarbonates
• This is due to relatively lower hydration energy.
• Hence, therefore Lithium is the alkali metal that forms bicarbonate only in aqueous solution.

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Answer 2

Concept:

Alkali Metals: The elements present in the first group of the periodic table are referred to as alkali metals. For eg: Li, Na, K, Rb etc.

Alkali metal bicarbonates: General formula for alkali meta bicarbonates is MHCO₃ where M is alkali metal.

Answer:

Lithium forms bicarbonate only in an aqueous solution.

Solution:

All alkali metals form bicarbonates in solid state except Lithium (Li).

Lithium bicarbonate has no existence in the solid state. Due to high hydration energy, it only exists in the form of an aqueous solution.

The second reason why lithium forms bicarbonate in only aqueous solution is its diagonal relationship with magnesium (Mg). Mg(HCO₃)₂ also exists in only aqueous form and hence lithium also forms it in only aqueous solution.

LiHCO₃  ------------> Li₂CO₃    [ -H₂O, -CO₂]

Hence the alkali metal which forms bicarbonate only in aqueous solution is Lithium (Li).

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