Question

Propyne and propene can be distinguished by

• A. concentrated $H_{2}S{O}_4$
• B. $B{r}_2$ in $CC{l}_4$
• C. dilute $KMn{O}_4$
• D. $AgN{O}_3$ in ammonia

Answer 1

Answer: (D)

Terminal alkynes forms silver salt with Tollen's reagent while alkene does not react with Tollen's reagent.
$C{H}_3-C\equiv C-H+AgN{O}_3\stackrel{N{H}_3(aq)}{\to }\underset{\text{white ppt}}{C{H}_3-C\equiv CAg\downarrow }$
Therefore, Tollen's reagent can be used to distinguish a terminal alkyne like propyne from alkene as well as from internal alkynes.