(i) Dry pellets of a base 'X' when kept in open absorbs moisture and turns sticky. The compound is also formed by chlor- alkali process. Write chemical name and formula of X. Describe chlor-alkali process with balanced chemical equation. Name the type of reactions occur when X is treated with dilute hydrochloric acid. Write the chemical equation.
(ii) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
CBSE Class X Science LA (5 Marks)
Answers
Answer:
(i) The base X is Sodium Hydroxide (NaOH)
When NaOH is kept in open, it absorbs mosture to form acquous NaOH which is sticky.
When electricity is passed through the aqueous solution of Sodium Chloride, it decomposes to form Sodium Hydroxide. This is called the chlor-alkali process because the products that are formed are chlorine (hence chlor) and Sodium Hydroxide which is alkaline (hence alkali).
The balanced chamical reaction is as follows:
NaCl (aq) + 2H₂O (l) → 2NaOH (aq) + Cl₂ (g) + H₂ (g)
When NaOH is treated with dilute Hydrochloric Acid (HCl), neutralisation reaction occurs. NaOH is a base while HCl is a acid. They react to form salt and water.
NaOH + HCl → NaCl + H₂O
(ii) If water is added to the concentrated acid, the heat generated may cause the mixture to splash out of the container and cause burns because dilution of concentrated acid is an exothermic process.
On the other hand, when acid is added to water, the solution that forms is very dilute amount of heat released is very small which is not enough to vaporize it. Therefore, it is always safer to add acid to water, and not water to acid.