Difference Between Alkanes And Alkenes

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Experiment 1: Alkanes & alkenes: Combustion and action of sulphuric acid.


To make careful observations and compare the difference(s) between alkanes and alkenes.


Hydrocarbons are composed exclusively of oxygen and hydrogen. There are three types of homogeneous hydrocarbons (whose members differ by one CH2 unit): alkanes, alkenes and alkynes. The difference between these three groups is in the bond types between the carbons. Alkanes form only single bonds, alkenes form double bonds, and in alkynes there is at least one triple bond.

Alkanes are hydrocarbons which is only contain single covalent bonds between carbon atoms. Alkenes are known as saturated hydrocarbon. This is because they have the maximum of covalent bonds per carbon atom. They have C-C and
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What are products of combustion of alkenes? How do they account for the sooty and luminous flame?

Ans: Alkenes are highly flammable with the presence of oxygen, and will give out product such as carbon dioxide gas and water. For example, ethylene burns as follow:
C2H4 + 3 O2 → 2 CO2 + 2 H2O
If the combustion of alkene is complete, it will give out a blue flame. On the other hand, as the number of atoms of carbon in the molecule increases, the combustion reaction tends to be less complete. The bigger the molecule of alkenes, the more likely to get a yellow, sooty flame.

B. Action of sulphuric acid (to be performed under fume hood)
1. When concentrated sulphuric acid was added into cyclohexane, is there any sign of reaction?

Ans: No.

2. Do the substances mix or are there two separate layers in the test tube when concentrated sulphuric acid was added into cyclohexene. Explain the reason behind the reaction.

Ans: The substances mix in the test tube when concentrated sulphuric acid was added into cyclohexene because they react by electrophilic addition to form alkyl hydrogen

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