I have a question on how to distinguish cyclohexane from benzene through lab tests i.e. chemical reactions (except for burning and observing the amount of soot produced, because it is not a very conclusive test)
So far the only thing I could think of is adding halogens to both of them. Since alkanes would undergo free radical substitution only in the presence of UV light or high temperature, whereas benzene would require the presence of a catalyst at room temperature. But I don't see how this would help tell them apart. Is there any decolonization involved for benzene or cyclohexane?
You might take a look at the reactions listed here. For example, hydrogenation with a catalyst looks good to me. The other reactions (adding a CH3 group etc) probably would work too.
But how does the reaction allow you to differentiate? There's no color change or effervescence that can help you differentiate the two reactions right?
To distinguish between cyclohexane and benzene through lab tests, there are a few chemical reactions you can perform that will provide distinct results.
1. Bromine water test:
a. Firstly, add a small amount of cyclohexane to a test tube.
b. Add a few drops of bromine water to the test tube and mix. If the cyclohexane is present, it will remain unchanged, and the bromine water will retain its orange color.
c. Repeat the same steps with benzene, and you will observe that the benzene decolorizes the bromine water, turning it colorless. This reaction occurs because benzene readily undergoes electrophilic aromatic substitution with the bromine.
2. Nitration test:
a. Add a small amount of cyclohexane to a test tube.
b. Drop by drop, add concentrated nitric acid (HNO3) to the test tube. Shake or stir the contents.
c. If the cyclohexane is present, you will observe no reaction or reaction only at high temperatures or with catalysts.
d. Repeat the same steps with benzene. Benzene readily undergoes electrophilic aromatic substitution reactions and reacts with nitric acid to form nitrobenzene, which will be evident by a change in color.
These two tests can differentiate cyclohexane from benzene based on their different reactivities. Cyclohexane, being an alkane, is less reactive and requires higher temperatures or catalysts to undergo reactions, whereas benzene, being an aromatic compound, undergoes reactions readily at room temperature.
Remember, when performing these tests, always follow proper safety precautions and work in a well-ventilated area or fume hood.