Question

Give one chemical test to distinguish between the following pairs:

Ethyne and ethene

Answer 1

Step 1:

Ethyne $\left({\mathrm{C}}_2{\mathrm{H}}_2\right)$ is a hydrocarbon that contains a Carbon-Carbon triple bond.

Ethene $\left({\mathrm{C}}_2{\mathrm{H}}_4\right)$ is a hydrocarbon that contains a Carbon-Carbon double bond.

Step 2: Chemical test

There is a test to distinguish between ethyne and ethene:

Treatment of Ammoniacal Silver Nitrate

When Ammoniacal Silver Nitrate $\left({\mathrm{AgNO}}_3\right)$ is added to Ethyne $\left({\mathrm{C}}_2{\mathrm{H}}_2\right)$ then it gives white precipitates. But when Ammoniacal silver nitrate is added to Ethene $\left({\mathrm{C}}_2{\mathrm{H}}_4\right)$, no reaction occurs and no precipitate is obtained.

Reaction with Ethyne and Ammoniacal Silver Nitrate is:

$$\begin{gathered} {\mathrm{C}}_2{\mathrm{H}}_2+2{\mathrm{AgNO}}_3+2{\mathrm{NH}}_4\mathrm{OH}\to {\mathrm{C}}_2{\mathrm{Ag}}_2+2{\mathrm{NH}}_4{\mathrm{NO}}_3+2{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Ethyne}\mathrm{White}\mathrm{ppt}. \end{gathered}$$

Reaction with Ethene and Ammoniacal Silver Nitrate is:

$$\begin{gathered} {\mathrm{C}}_2{\mathrm{H}}_4+2{\mathrm{AgNO}}_3+2{\mathrm{NH}}_4\mathrm{OH}\to \mathrm{no}\mathrm{reaction} \\ \mathrm{Ethene} \end{gathered}$$