Match each chemical process or reagent involving alkenes and alkynes in Column A with its … — JAMB UTME

Match each chemical process or reagent involving alkenes and alkynes in Column A with its corresponding chemical observation or primary product in Column B.

Hydrolysis of calcium carbide ( $\text{CaC}_2$ )Laboratory preparation of ethyne gas ( $\text{C}_2\text{H}_2$ )
Treatment of propene ( $\text{CH}_3\text{CH}=\text{CH}_2$ ) with bromine in $\text{CCl}_4$ Decolorization of the reddish-brown solution due to halogen addition across the double bond
Treatment of but-1-yne ( $\text{CH}_3\text{CH}_2\text{C}\equiv\text{CH}$ ) with ammoniacal $\text{AgNO}_3$ solutionFormation of a white precipitate of silver alkynide due to the presence of an acidic terminal hydrogen
Treatment of but-2-yne ( $\text{CH}_3\text{C}\equiv\text{CCH}_3$ ) with ammoniacal $\text{AgNO}_3$ solutionNo visible reaction because of the absence of an acidic hydrogen on the triply-bonded carbon

Answer

The correct pairing links calcium carbide hydrolysis to ethyne gas preparation, propene with bromine in carbon tetrachloride to reddish-brown decolorization, but-1-yne with ammoniacal silver nitrate to white precipitate formation, and but-2-yne with ammoniacal silver nitrate to no visible reaction.

Hydrolysis of calcium carbide is a standard laboratory preparation of ethyne gas. Electrophilic addition of bromine across the double bond of propene decolorizes the reddish-brown bromine solution, demonstrating general unsaturation. Ammoniacal silver trioxonitrate(V) reacts specifically with terminal alkynes like but-1-yne because of their acidic terminal hydrogens to form a white silver alkynide precipitate, whereas internal alkynes like but-2-yne lack a terminal acidic hydrogen and show no reaction.

Step-by-Step Solution

Identify the preparation method for ethyne

Calcium carbide reacts with water according to

\text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_2 + \text{Ca(OH)}_2

, yielding ethyne gas.

This is the primary laboratory method for generating ethyne.

Evaluate the reaction testing for general unsaturation in propene

Bromine in

\text{CCl}_4

adds across the carbon-carbon double bond of propene to form 1,2-dibromopropane.

The consumption of molecular bromine causes the reddish-brown color of the solution to discharge.

Distinguish between terminal and internal alkynes using ammoniacal silver trioxonitrate(V)

But-1-yne possesses a terminal

\text{C}\equiv\text{C-H}

bond with an acidic proton that forms a white silver alkynide precipitate, whereas internal but-2-yne lacks terminal hydrogen atoms and gives no precipitate.

Ammoniacal

\text{AgNO}_3

selectively reacts only with terminal alkynes based on terminal hydrogen acidity.

Key Concept

Unsaturation testing, ethyne synthesis, and differentiation of terminal from internal alkynes

Estimated Time:1m 30s

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