Given below are two statements : Statement I : One mole of propyne reacts with excess of sodium to liberate half a mole of H2 gas. Statement II : Four g of propyne reacts with NaNH2 to liberate NH3 gas which occupies 224 mL at STP. In the light of the above statements, choose the most appropriate answer from the options given below: (1) Statement I is correct but Statement II is incorrect. (2) Both Statement I and Statement II are incorrect (3) Statement I is incorrect but Statement II is correct (4) Both Statement I and Statement II are correct.
Detailed Explanation
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Simple Explanation (ELI5)
Imagine a Lego stick (propyne)
It has a special block (the hydrogen directly attached to the triple bond) that can be popped off quite easily when it meets certain metals or bases.
- When it meets shiny sodium metal (Na), two Lego sticks have to pop off one special block each to give one full hydrogen gas balloon (H2). That means one stick only makes half a balloon.
- When it meets a powerful Lego-popper called sodamide (NaNH2), every stick pops off one special block and sends out one puff of ammonia gas (NH3).
If you know how many sticks you have and how many puffs or balloons each reaction makes, you can count the volume of gas using the rule: 1 mole of any gas = 22.4 L at STP. That’s like saying every full balloon has the same size under standard conditions.
Step-by-Step Solution
Step 1: Molar mass of propyne
Propyne has the formula .
Statement I
Reaction with metallic sodium:
From the equation: propyne → .
Therefore propyne → .
Statement I is correct.
Statement II
-
Given mass of propyne:
-
Reaction with :
Thus 1 mol propyne → 1 mol .
-
Volume of at STP:
The statement claims 224 mL, which corresponds to only 0.01 mol . Therefore Statement II is incorrect.
Final choice
Only Statement I is correct → Option (1).
Examples
Example 1
Acetylene cylinders used in welding—acetylene reacts with sodamide to generate acetylide salts in synthetic chemistry.
Example 2
Preparation of alkynyl sodium salts for nucleophilic substitution in pharmaceutical synthesis.
Example 3
Use of molar volume to quickly estimate gas quantities in laboratory reactions and titrations.