Alkali Earth Metals' Carbonates Decomposition | Temperature

Alkali earth metals' carbonates decomposes to metal oxide and carbon dioxide gas under high temperature. These carbonates are insoluble in the water.

MCO3(s) → MO(s) + CO2(g)
M = Be , Mg, Ca, Sr, Ba
MO - alkali earth metal oxide
CO2 - Carbon dioxide




Example for decomposition

Magnesium carbonate decomposes to magnesium oxide and carbon dioxide at 3500C.

HEAT + MgCO3(s) → MgO(s) + CO2(g)


How do identify a decomposition is happening?

We can notice a emission of gas at the decomposition to identify the reaction.



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 are mentioned below.

  • MgCO3 - 1170C
  • CaCO3 - 1780C
  • SrCO3 - 2350C
  • BaCO3 - 2670C



Why decomposition temperature of carbonate is increased when go down the group?

Ionic radius of alkali earth metals are decreased when go down the group. Therefore polarizing ability is decreased. As an example, polarizing ability of Mg is higher than Ca. 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


ANSWER

Lithium carbonate (Li2CO3) is the only carbonate in the alkali metals not stable to heating and it decomposes to lithium oxide (Li2O and) carbon dioxide (CO2).


Magnesium carbonate (MgCO3) also decomposes to MgO and CO2.


Both Li2O and MgO are white solids. Therefore we cannot identify Li2CO3 and MgCO3 by considering decomposition only.

Solubility of Li2O and MgO

But, if we add produced Li2O and MgO to water separately, a white precipitate is deposited in one beaker. We know, metal oxides give metal hydroxides in 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 metal carbonates

  • Alkali metal carbonates except lithium carbonate, do not decompose.
  • All alkali earth metal carbonates decompose.


Questions


Does magnesium carbonate decompose 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.



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