Alkali Earth Metals' Carbonates Decomposition on Heating

Alkali earth metals' carbonates decomposes to metal oxide and carbon dioxide gas under higher temperature conditions. These alkali earth metal carbonate compounds are insoluble in the water.

MCO_3(s) → MO_(s) + CO_2(g)

M = Be , Mg, Ca, Sr, Ba
MO - alkali earth metal oxide
CO₂ - Carbon dioxide

decomposition temperatures of alkali earth metals' carbonates

Content

Example for decomposition reactions
- How do identify decomposition is happening when heat is supplied?
Decomposition temperatures of alkali earth metals' carbonates
- Why decomposition temperature of alkali earth metal carbonate compounds are increased when going down the group 2?
Can you separate lithium carbonate and magnesium carbonate by decomposition method? | Li₂CO₃ and MgCO₃ decomposition
- Step 1: heating each carbonate separately
- Step 2: Observe solubility of Lithium oxide and Magnesium oxide in water
Decomposition of other metal carbonates
Questions asked by Students

Example for decomposition reactions

Magnesium carbonate decomposes to magnesium oxide and carbon dioxide at 350⁰C temperature. Therefore, you can observe weight of white colour Magnesium carbonate solid is reducing and a colourless gas is released during the decomposition period.

HEAT + MgCO_3(s) → MgO_(s) + CO_2(g)

How do identify decomposition is happening when heat is supplied?

We can notice an emission of colourless gas at the decomposition to identify the reaction. Because carbon dioxide gas is released during the decomposition, we can send the gas to the limewater to observe the formation of white precipitate of calcium carbonate.

Decomposition temperatures of alkali earth metals' carbonates

Decomposition temperature is increased when go down the group. As an example, CaCO₃ decomposition temperature is higher than MgCO₃.

Decomposition temperatures of alkali metal carbonate compounds are mentioned below.

Beryllium carbonate (BeCO₃) - Anhydrous BeCO₃ is unstable and decomposes readily to BeO and CO₂.
Magnesium carbonate (MgCO₃) - 350⁰C
Calcium carbonate (CaCO₃) - 825⁰C
Strontium carbonate (SrCO₃) - 1100⁰C
Barium carbonate (BaCO₃) - 1300⁰C

Why decomposition temperature of alkali earth metal carbonate compounds are increased when going down the group 2 ?

Ionic radius of alkali earth metals are increased when go down the group. Therefore polarizing ability is decreased. As an example, polarizing ability of Magnesium +2 cation is higher than Calcium +2 cation. So, polarization ability is increased more and more, negative ions' distortion is increased.

Question

Can you separate lithium carbonate and magnesium carbonate by decomposition method? | Li₂CO₃ and MgCO₃ decomposition

Step 1: heating each carbonate separately

Answer

Lithium carbonate (Li₂CO₃) is the only carbonate in the alkali metals which is not stable to heating and it decomposes to lithium oxide (Li₂O) and carbon dioxide (CO₂) gas.
Magnesium carbonate (MgCO₃) also decomposes to Magnesium oxide and Carbon dioxide gas.
Both Li₂O and MgO are white solids. Therefore we cannot identify Li₂CO₃ and MgCO₃ by considering decomposition only.

Step 2: Observe solubility of Lithium oxide and Magnesium oxide in water

But, if we add formed Li₂O and MgO to water separately, a white precipitate is deposited in one beaker. We know, metal oxides give metal hydroxides when they are added in to the water.
Therefore, LiOH and Mg(OH)₂ are given by Li₂O and MgO respectively. LiOH is water soluble and Mg(OH)₂ is the compound which is deposited as a white precipitate in one beaker.
From that, we can identify MgCO₃ from Li₂CO₃.

Decomposition of other metal carbonates

Alkali metal carbonates except lithium carbonate, do not decompose to metal oxide and carbon dioxide.
All alkali earth metal carbonates decompose as described earlier.
Most of d block and p block metal carbonates also decomposes to metal oxide and carbon dioxide gas.

Questions asked by students

Which alkali metal carbonate gives CO₂ on heating?

Only Lithuum carbonate give Carbon dioxide gas on heating while all other alkali metal carbonates are stable to heat.

Does magnesium carbonate decomposes when heated?

Yes. Magnesium carbonate decomposes to magnesium oxide (MgO) and carbon dioxide (CO₂) when heated.

Decomposition of magnesium oxide

Magnesium oxide is stable to heat. So it does not decomposes furthermore when heat is supplied. Magnesium oxide can be obtained by the decomposition of Magnesium carbonate.

Which alkali metal carbonate decomposes on heating?

Only Lithium carbonate decomposes to Lithium oxide and carbon dioxide. All other alkali metal carbonates such as Sodium carbonate, Potassium carbonate are stable to heat.