Question

Name the following and give equations for these reactions:
a) A white solid, which when heated, leaves behind a yellow solid and gives CO2.
b) A bluish green powder, on heating, leaves behind a black solid and gives CO

Answer 1

Explanation:

CuCO3(g)→CO2(g)+CuO(s)

Therefore, the green substance is a compound and the change is a chemical change since giving off a gas is one of the several indication of a chemical change that include:

1 Gas evolution

2 Formation of a precipitate

3 Evolution of heat

4 Odor

5 Color change etc.

The question describes an experiment similar to the decomposition of copper(II) carbonate (CuCO3) which is when heated in decomposes into carbon dioxide gas (CO2) and copper(II) oxide (CuO)

Answer 2

(a) The white solid is lead carbonate, and the yellow solid product is Lead oxide. The reaction is as follows -

Δ

PbCO₃(s) ------------> PbO(s) + CO₂ (g)

(b) The bluish green solid is Copper carbonate, and the black solid product is Copper oxide. The reaction is as follows -

Δ

CuCO₃ (s)-------------> CuO(s) + CO₂ (g)

• In the first sentence, The white solid is lead carbonate as it undergoes a thermal decomposition to form a yellow solid precipitate of lead oxide and releases carbon dioxide
• The reaction is represented as-

Δ

PbCO₃(s) ------------> PbO(s) + CO₂ (g)

• In the second sentence, the reactant given is blue this implies that the reactant is probably a copper compound as most copper compounds are blue
• Metal carbonates on heating give off Carbon dioxide, So the most probable compound is copper carbonate.
• The reaction is a decomposition reaction, represented as-

Δ

CuCO₃ (s)-------------> CuO(s) + CO₂ (g)

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