Question

A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a by-product of the chlor-alkali process. What type of reaction occurs when B is treated with an acidic oxide?
A ) Precipitation reaction.
B ) Neutralization reaction.
C ) Endothermic reaction.
D ) Exothermic reaction.

Answer 1

Hint: In a neutralization reaction, an acid reacts with a base to form salt and water. Similarly, in a neutralization reaction, an acidic oxide reacts with a base to form salt and water. Chlor-alkali process is used to manufacture chlorine gas from the electrolysis of brine solution.

Complete answer:
Bases such as sodium hydroxide are hygroscopic in nature as they absorb moisture from the surroundings. Hence, when a dry pellet of sodium hydroxide is kept in open it absorbs moisture from the surrounding. After absorption of moisture, the sodium hydroxide pellet becomes sticky.
During the chlor-alkali process, brine solution is electrolyzed. Brine is aqueous sodium chloride solution. During electrolysis, brine solution decomposes to give hydrogen gas, chlorine gas and sodium hydroxide. Write the balanced chemical equation for the electrolysis of brine solution:
\[{\text{2NaCl(aq) + 2}}{{\text{H}}_{\text{2}}}{\text{O(l)}} \to {\text{2NaOH(aq) + }}{{\text{H}}_{\text{2}}}{\text{(g) + C}}{{\text{l}}_{\text{2}}}{\text{(g)}}\]
In the above process, sodium hydroxide is a byproduct. Thus, the base B is sodium hydroxide.

Acidic oxides react with bases to form salt and water. The reaction of sodium hydroxide with an acidic oxide (such as sulphur trioxide ) gives salt and water.
\[{\text{2NaOH(aq) + S}}{{\text{O}}_{\text{3}}}{\text{(aq)}} \to {\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_4}{\text{(aq) + }}{{\text{H}}_{\text{2}}}{\text{O(l)}}\]
Similarly, sodium hydroxide reacts with phosphorus pentoxide to form sodium phosphate and water.
\[{\text{6NaOH(aq) + }}{{\text{P}}_2}{{\text{O}}_{\text{5}}}{\text{(aq)}} \to {\text{2N}}{{\text{a}}_3}{\text{P}}{{\text{O}}_4}{\text{(aq) + 3}}{{\text{H}}_{\text{2}}}{\text{O(l)}}\]
The reaction of sodium hydroxide ( a base) with acidic oxides (acids ) is a neutralization reaction.
In a precipitation reaction, two clear, aqueous solutions are combined to form a precipitate.
In an endothermic reaction, heat energy is supplied whereas in an exothermic process, heat energy is given out.

Hence, the option (B) is the correct option.

Note: Oxides and hydroxides of alkali metals, and alkaline earth metals are basic in nature.
Oxides and hydroxides of nonmetals are acidic in nature.