Terminal alkynes such as ethyne react with ammoniacal silver nitrate to give a precipitate because
- A. the triple bond adds silver
- B. the hydrogen attached to the triply bonded carbon is weakly acidic and is replaced by silver
- C. silver catalyses polymerisation
- D. alkynes are strong bases
Explanation
The sp hybridised carbon holds its bonding electrons closer, so the attached hydrogen is slightly acidic and can be replaced by a metal to form an acetylide precipitate, which is the standard test distinguishing a terminal alkyne from an internal one. Alkenes and alkanes give no such reaction. The dry precipitates are explosive and must be destroyed with acid.