Consider the following sequence of reactions to give the major product $$(X)$$:

$$P$$ g of the major product $$(X)$$ formed is reacted with $$\text{NaHCO}_3$$ solution to liberate a gas which occupied 11.2 dm³ at STP. $$P$$ = _____ g.
( Given molar mass in g $$mol^{-1} H:1,C:12,O:16,Cl:35.5$$)

$$\text{CH}_3\text{Cl} / \text{Anhydrous AlCl}_3$$ (Friedel-Crafts Alkylation):

Benzene reacts with methyl chloride in the presence of a Lewis acid to form Toluene ($$\text{C}_6\text{H}_5\text{CH}_3$$).

$$\text{Cl}_2 / \text{FeCl}_3$$ (Electrophilic Aromatic Substitution): The methyl ($$-\text{CH}_3$$) group on toluene is an ortho/para-directing group. Due to steric hindrance at the ortho-position, the para-isomer is formed as the major product. This gives $$p$$-chlorotoluene.

$$\text{K}_2\text{Cr}_2\text{O}_7 / \text{H}_2\text{SO}_4$$ (Oxidation):

Potassium dichromate in an acidic medium is a strong oxidizing agent. It oxidizes the benzylic alkyl group ($$-\text{CH}_3$$) completely into a carboxylic acid group ($$-\text{COOH}$$). The chlorine atom remains unaffected.

Thus, the major product ($$X$$) is $$p$$-chlorobenzoic acid ($$\text{Cl}-\text{C}_6\text{H}_4-\text{COOH}$$).

The molecular formula of $$p$$-chlorobenzoic acid is $$\text{C}_7\text{H}_5\text{O}_2\text{Cl}$$.

Using the given atomic masses:

• $$\text{C} = 12 \times 7 = 84$$
• $$\text{H} = 1 \times 5 = 5$$
• $$\text{O} = 16 \times 2 = 32$$
• $$\text{Cl} = 35.5 \times 1 = 35.5$$

$$\text{Molar Mass of } X = 84 + 5 + 32 + 35.5 = 157.5\text{ g mol}^{-1}$$

Carboxylic acids react with sodium bicarbonate ($$\text{NaHCO}_3$$) to liberate carbon dioxide ($$\text{CO}_2$$) gas according to the following balanced equation:

$$\text{R-COOH} + \text{NaHCO}_3 \rightarrow \text{R-COONa} + \text{H}_2\text{O} + \text{CO}_2\uparrow$$

From the stoichiometry of the reaction:

$$\text{1 mole of } \text{R-COOH} \text{ liberates } \text{1 mole of } \text{CO}_2\text{ gas}$$

• Given volume of $$\text{CO}_2$$ liberated = $$11.2\text{ dm}^3$$
• Moles of $$\text{CO}_2$$ = $$\frac{11.2}{22.4} = 0.5\text{ moles}$$

Since the molar ratio between $$p$$-chlorobenzoic acid and $$\text{CO}_2$$ is $$1:1$$:

$$\text{Moles of major product } (X) = 0.5\text{ moles}$$

Now, find the mass $$P$$:

$$\text{Mass } P = \text{Moles} \times \text{Molar Mass}$$ 

$$P = 0.5 \times 157.5 = 78.75\text{ g}$$