Question

Dry pellets of base 'X' when kept in open absorb moisture and turn sticky. The compound is also formed by chlor-alkali process. Write chemical name and formula of X. Describe chlor-alkali process with a balanced chemical equation. Name the type of reaction that occurs when X is treated with dilute hydrochloric acid. Write the chemical equation. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Answer 1

Substance ‘X’

1. Substance ‘X’ is sodium hydroxide $\left(\mathrm{NaOH}\right)$.
2. Sodium hydroxide absorbs moisture and becomes sticky.

Chlor-alkali process

1. Sodium hydroxide is produced on an industrial scale by passing an electric current through a concentrated aqueous solution of sodium chloride $\left(\mathrm{NaCl}\right)$, also called brine.
2. The process is called chlor-alkali process, in which ‘chlor’ comes from chlorine produced and ‘alkali’ comes from sodium hydroxide produced.
3. In this process sodium chloride and water react in presence of electricity to form sodium hydroxide, hydrogen gas $\left({\mathrm{H}}_2\right)$ and chlorine gas $\left({\mathrm{Cl}}_2\right)$.

$2\mathrm{NaCl}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{\mathrm{Electric}\mathrm{Current}}{\to }2\mathrm{NaOH}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$

In this reaction, hydrogen gas is evolved at the cathode and chlorine at the anode.

Neutralization reaction

1. In a neutralization reaction, an acid and a base react to form neutral salts and water.
2. The reaction of sodium hydroxide with hydrochloric acid $\left(\mathrm{HCl}\right)$ is an example of a neutralization reaction.

The reaction of sodium hydroxide with hydrochloric acid.

Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.

$\mathrm{NaOH}\left(\mathrm{aq}\right)+\mathrm{HCl}\left(\mathrm{aq}\right)\to \mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Addition of acid to water

1. Acids have a high affinity for water and thus, the process of dilution of acid is highly exothermic (a reaction in which a lot of heat is produced).
2. If water is added to acid the reaction taking place with generate so much heat that the beaker may break and it may lead to accidents.
3. This is why for diluting acids, acids are slowly added to water with continuous stirring to avoid the generation of too much heat at once