Question

Choose the salt that most appropriately fits the description given in the following

[AgCl, MgCl_2, NaHSO₄, PbCO₃ , ZnCO₃, , KCO_3, Ca(NO)₃]

On heating this salt gives a yellow residue when hot and white when cold

Answer 1

Correct answer is Zinc Carbonate

• Zinc carbonate is a white coloured substance
• On heating, it decomposes and zinc oxide (ZnO) is formed
• ${\mathrm{ZnCO}}_3\underset{\mathrm{yellow}}{\stackrel{∆}{\to }\mathrm{ZnO}}+{\mathrm{CO}}_2$
• On cooling some physical changes happens and whit precipitate of zinc oxide is formed
• $\underset{\mathrm{yellow}}{\mathrm{ZnO}}\stackrel{\mathrm{cooling}}{\to }\underset{\mathrm{white}}{\mathrm{ZnO}}$