Question

From the list of the following salt choose the salt that most appropriately fits the description given in the following.

[AgCl, MgCl₂, NaHSO₄, PbCO₃, ZnCO₃, KNO₃,Ca(NO₃)]

1. A deliquescent salt.
2. An insoluble Chloride
3. On heating this salt gives yellow residue when hot white when cold.
4. On heating this salt a brown colored gas is evolved.

Answer 1

1. A deliquescent salt.------------MgCl₂

Magnesium chloride is a deliquescent substance that absorbs atmospheric water vapour until it eventually dissolves into a saturated solution.

2. An insoluble Chloride----------AgCl

It is a crystalline solid white in color. It does not dissolve in water, alcohols and dilute acids.

3. On heating this salt gives yellow residue when hot, and white when cold.---------ZnCO₃

• On heating Zinc carbonate thermal decomposition takes place.
• It is a white solid powdery substance.
• When it strongly heated it forms a yellow solid substance. CO₂ gas is evolved.

ZnCO₃ (s) $\stackrel{\mathrm{heat}}{\to }$ ZnO (s) + CO₂(g)

• When this left to cool the yellow zinc oxide turns white.

4. On heating this salt a brown colored gas is evolved. -----------Ca(NO₃)₂

• On heating Calcium Nitrate, it undergoes decomposition and releases nitrogen dioxide and oxygen.

Ca(NO₃)₂ (s) ⇢ CaO (s) + 2NO₂ (g) + ½ O₂ (g)

• The reddish brown gas evolved is Nitrogen dioxide.