Question

When heated, X solid gives off a gas, this gas is bubbled through lime water, a white precipitate is formed. The residue after heating solid X reacts with dilute acid and also aqueous alkali.
What is X?

Answer 1

X might be the Calcium Carbonate

Answer 2

Here, X refers to Calcium carbonate CaCO3.

Justification for the answer:

• when metal carbonates are heated, they get decomposed and forms oxides of their metal.[here carbon oxide]
• They also liberate a gas on heating.
• that particular gas is Carbon dioxide CO2.
• when carbon dioxide CO2 is bubbled/ mixed with lime water it turns the lime water milky and forms a white precipitate.
• The equation for the above reaction is- CaCO3(s)=>Δ CaO(s) + CO2(g)
• In the above reaction, the residue after heating that is Calcium oxide also reacts with dilute acids such as dilute. HCl and produces water as a product.
• The residue also reacts with aqueous alkalis.
• The above reaction of calcium carbonate CaCO3 is a type of thermal decomposition reaction.