JEE Main 2025 Jan 22 Shift 1, Chemistry Q11: Properties of Alkynes

JEE Main2025Jan 22, Shift 1Chemistry

Given below are two statements :

Statement I : One mole of propyne reacts with excess of sodium to liberate half a mole of H $_{2}$ gas.

Statement II : Four g of propyne reacts with NaNH $_{2}$ to liberate NH $_{3}$ gas which occupies 224 mL at STP.

In the light of the above statements, choose the most appropriate answer from the options given below:

A
Statement I is correct but Statement II is incorrect.
B
Both Statement I and Statement II are incorrect
C
Statement I is incorrect but Statement II is correct
D
Both Statement I and Statement II are correct.

Solution

Propyne (CH $_{3}$ $-$ C $\equiv$ CH) has one acidic terminal $\equiv$ C $-$ H. With Na, one mole of propyne releases $\frac{1}{2}$ mole H $_{2}$ (one H removed per molecule). Statement I is correct.

For Statement II: molar mass of propyne $= 40$ g/mol, so $4$ g $= 0.1$ mol. With NaNH $_{2}$ , this liberates $0.1$ mol NH $_{3}$ . At STP, $0.1$ mol of gas occupies $0.1 \times 22400 = 2240$ mL, not $224$ mL. Statement II is incorrect.

$∴$ Statement I correct, Statement II incorrect.

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JEE Main 2025 Jan 22 Shift 1, Chemistry Q11: Properties of Alkynes

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