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.
MCO3(s) → MO(s) + CO2(g)
- M = Be , Mg, Ca, Sr, Ba
- MO - alkali earth metal oxide
- CO2 - Carbon dioxide
- 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 + MgCO3(s) → MgO(s) + CO2(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
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
Can you separate lithium carbonate and magnesium carbonate by decomposition method? | Li2CO3 and
Step 1: heating each carbonate separately
- 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
Potassium carbonate are stable to heat.