Hydrocarbons 2 Question 25
25. Propyne and propene can be distinguished by
(2000)
(a) conc. $\mathrm{H}{2} \mathrm{SO}{4}$
(b) $\mathrm{Br}{2}$ in $\mathrm{CCl}{4}$
(c) dil. $\mathrm{KMnO}_{4}$
(d) $\mathrm{AgNO}_{3}$ in ammonia
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Answer:
Correct Answer: 25. (c)
Solution:
- Terminal alkynes forms silver salt with Tollen’s reagent while alkene does not react with Tollen’s reagent.
$$ \mathrm{CH}{3}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}+\mathrm{AgNO}{3} \stackrel{\mathrm{NH}{3}(a q)}{\longrightarrow} \mathrm{CH}{3} \underset{\text { white ppt. }}{\mathrm{C} \equiv \mathrm{CAg} \downarrow} $$
Therefore, Tollen’s reagent can be used to distinguish a terminal alkyne like propyne from alkene as well as from internal alkynes.
