How can you distinguish between an alkane and an alkene using a laboratory test?

How can you distinguish between an alkane and an alkene using a laboratory test?

• A. By measuring boiling points
• B. By performing a bromine test; alkenes will decolorize bromine water
• C. By using infrared spectroscopy
• D. By examining the refractive index

Answer: (B)

The bromine test is a straightforward and effective method for distinguishing between an alkane and an alkene in the laboratory. Alkenes contain a carbon-carbon double bond (C=C) which is reactive, allowing them to participate in reactions such as the addition of bromine. When bromine water, which is typically a reddish-brown solution of bromine in water, is added to an alkene, the double bond reacts with bromine, leading to the formation of a colorless dibromide compound. As a result, the reddish-brown color of the bromine water disappears, indicating the presence of an alkene. In contrast, alkanes, which only contain single bonds (C-C), do not undergo this reaction and hence do not decolorize bromine water. Therefore, the immediate color change observed in the bromine test is a reliable indicator of an alkene. In regard to the other laboratory techniques mentioned, measuring boiling points may provide some information about the purity of the compound, but it is not definitive for distinguishing between alkanes and alkenes since both types of compounds can have overlapping boiling ranges. Infrared spectroscopy can identify functional groups and double bonds, but it requires more complex analysis and does not provide an

The bromine test is a straightforward and effective method for distinguishing between an alkane and an alkene in the laboratory. Alkenes contain a carbon-carbon double bond (C=C) which is reactive, allowing them to participate in reactions such as the addition of bromine. When bromine water, which is typically a reddish-brown solution of bromine in water, is added to an alkene, the double bond reacts with bromine, leading to the formation of a colorless dibromide compound. As a result, the reddish-brown color of the bromine water disappears, indicating the presence of an alkene.

In contrast, alkanes, which only contain single bonds (C-C), do not undergo this reaction and hence do not decolorize bromine water. Therefore, the immediate color change observed in the bromine test is a reliable indicator of an alkene.

In regard to the other laboratory techniques mentioned, measuring boiling points may provide some information about the purity of the compound, but it is not definitive for distinguishing between alkanes and alkenes since both types of compounds can have overlapping boiling ranges. Infrared spectroscopy can identify functional groups and double bonds, but it requires more complex analysis and does not provide an