Question

The reagent which is used to distinguish between propene and propyne is-
A. Bromine
B. Alkaline KMnO₄
C. Ammoniacal AgNO₃
D. Ozone

Answer 1

Hint: The chemicals that are used to bring a specific change in the organic compounds that can only be done using that specific chemical are called reagents. Reactant reacts with the reagents to give the product. The reagents are also used to test if a particular compound gives specific tests or not.

Complete Step by Step Answer:
This test is called the Ammoniacal silver nitrate test. Ammoniacal AgNO₃ is commonly known as Tollen’s reagent. Now to distinguish between propene and propyne we are going to need a reagent that is basic in nature. Because in propyne the sp hybridised carbon is more electronegative than the sp² hybridised propene carbon thus the hydrogen attached to the sp hybridised carbon is much more acidic than the hydrogen attached to the sp² hybridised carbon. That is also called as S character which means the percentage of s orbital in the hybridization, if the percentage of s in hybridization is more the atom is more electronegative and if it is less the atom is less electronegative and Hydrogen attached to a more electronegative atom or substance is more acidic.

So,
$CH_3-C \equiv C-H + AgNO_3 (in\ NH_3) \longrightarrow CH_3-C \equiv C-Ag + HNO_3$
Here CH₃—C≡C—Ag is a white ppt.
$CH_3-CH=CH_2+AgNO_3(in\ NH_3) \longrightarrow No\ reaction$

Since it is a property of tollen’s reagent to react with the acidic hydrogen it gives white ppt with propyne and no reaction with propene so thus we can distinguish between them using tollen’s reagent.
Thus, Option (C) is correct

Note: Tollen’s reagent is generally used as a reagent to distinguish between aldehyde and ketone. The aldehyde and ketone must have alpha hydrogen. It is prepared in the laboratory using AgNO₃, NaOH and NH₃.