Question

1) An unknown compound is found to burn in oxygen. When bromine is added to this unknown, the solution remains orange. What can be said about the unknown compound?

2)When a purple solution of KMnO4 is added to a different unknown, a brown precipitate forms. What can be said about this unknown?

Answer 1

Answer-1)

a) Br2 test for Unsaturation: On addition of Br2 solution to unknown organic compound if brown colour brominr Br2 changed it indicates the presence of unsaturation i.e. C C double or/and triple bond.

The reaction is ,

R2C=CR2 + Br2 -------> R2BrC-CBrR2

brown colourles

The reason for consumption of Br2 on addition.

For given unknown as no colour change observed it meand in an unknown no Unsaturation site of C=C kind present.

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Answer-2)

a) KMnO4 test for unsaturation : On addition of pink coloured KMnO4 solution to an organic compound if pink colour changes and in addition to it if a brown ppt forms it indicates presence of unsaturation sites like C=C.

Reaction:

C=C + KMnO4 + H2O ---------> HO-C-C-OH + MnO₂ (brown ppt)

Pink colour

In case of given unknown this is only the observation and hence we can say that an unknown is an alkene or contain at least one C=C functionality.

Hence the observations and inferences

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