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. (1 mark)

(b) Find the cation and the anion present in Calcium sulphate. (1 mark)

(c) "Sodium chloride and washing soda both belong to the same family of salts." Justify this statement. (2 marks)

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. (2 marks)

Detailed answers for each sub-question:

(a) Sodium chloride ($NaCl$) is formed from the reaction of hydrochloric acid ($HCl$) and sodium hydroxide ($NaOH$).

(b) In Calcium sulphate ($CaSO_4$), the cation is the calcium ion ($Ca^{2+}$) and the anion is the sulphate ion ($SO_4^{2-}$).

(c) Sodium chloride ($NaCl$) and washing soda ($Na_2CO_3$) both belong to the same family of salts because they share the same positive radical (cation), which is the sodium ion ($Na^+$). Salts containing the same cation or anion are classified under the same family.

OR

(c)

• pH Scale: A scale developed for measuring hydrogen ion concentration in a solution is called the pH scale. The 'p' in pH stands for 'potenz', which means power in German. The scale ranges from 0 (highly acidic) to 14 (highly alkaline), with 7 being neutral.
• Salt formed: The reaction between potassium hydroxide ($KOH$) and sulphuric acid ($H_2SO_4$) produces potassium sulphate ($K_2SO_4$) and water:

$$2KOH(aq) + H_2SO_4(aq) \rightarrow K_2SO_4(aq) + 2H_2O(l)$$

• pH value: Since potassium sulphate is a salt of a strong base ($KOH$) and a strong acid ($H_2SO_4$), it is a neutral salt. Therefore, the pH value of its aqueous solution is $7$.