Question

Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them.
(a) Identify the acid and base from which Sodium chloride is formed.
(b) Find the cation and the anion present in Calcium sulphate.
(c) “Sodium chloride and washing soda both belong to the same family of salts.” Justify this statement.
OR
(c) Define the term pH scale. Name the salt obtained by the reaction of Potassium hydroxide and Sulphuric acid and give the pH value of its aqueous solution.

Answer 1

(a) Sodium chloride (NaCl) is formed from the reaction of:
Acid: Hydrochloric acid ($\text{HCl}$).
Base: Sodium hydroxide ($\text{NaOH}$).
$\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}.$

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(b) Calcium sulphate ($\text{CaSO}_4$) contains:
Cation: Calcium ion ($\text{Ca}^{2+}$).
Anion: Sulphate ion ($\text{SO}_4^{2-}$).

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(c) Sodium chloride ($\text{NaCl}$) and washing soda ($\text{Na}_2\text{CO}_3$) both belong to the family of salts containing the sodium ( (Na+) cation. They are classified as salts of strong bases (like $\text{NaOH}$) and acids:
Sodium chloride is formed from $\text{HCl}$ and $\text{NaOH}$.
Washing soda is formed from carbonic acid ($\text{H}_2\text{CO}_3$) and $\text{NaOH}$.
Both salts share the same cation ($\text{Na}^+$), making them part of the same family.

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Definition of pH scale: The pH scale is a logarithmic scale used to measure the acidity or alkalinity of an aqueous solution. It ranges from 0 (strongly acidic) to 14 (strongly basic), with 7 being neutral.
Salt obtained: Potassium sulphate ($\text{K}_2\text{SO}_4$).
pH value: The pH of an aqueous solution of $\text{K}_2\text{SO}_4$ is 7 (neutral), as it is a salt of a strong acid ($\text{H}_2\text{SO}_4$) and a strong base ($\text{KOH}$).
$2\text{KOH} + \text{H}_2\text{SO}_4 \rightarrow \text{K}_2\text{SO}_4 + 2\text{H}_2\text{O}.$