JAMB - Chemistry (1986 - No. 23)
A white solid suspected to be lead trioxonitrate (V) zinc trioxocarbonate (IV) or calcium trioxocabonate (IV) was heated strongly. Its residue which was yellow when hot and white when cold is?
lead (II) oxide
calcium oxide
zinc oxide
lead nitrate
Vysvětlení
Zinc oxide is an amphoteric oxide, meaning it can react with both acids and bases. It's typically white at room temperature, but when heated, it loses oxygen and turns yellow. This color change is reversible, and the oxide reverts to white upon cooling.
The amphoteric oxide that is yellow when hot and white when cold is zinc oxide (ZnO).