Tests to distinguish between alkanes and alkenes
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ALKELENES Properties :: 1) first three Alkenes, ethylene, propylene & α-butylene are gases . next few members are liquid. higher members are solid.
2) except ethylene, all other Alkenes are colourless & odourless. ethylene is a colourless gas with sickly sweet Odour.
3) they are insoluble in water but quite soluble in organic solvents like benzene, ether, chloroform, etc.
4) boiling point of Alkenes increase with increase with increase in molecular mass. A rise of 20 to 30 degree is observed for each added carbon atom.
5) as in Alkanes, Alkenes with branching lowers boiling point.
ALKANES Properties ::
1)alkanes are colourless & odourless.
2) at room temperature, first four alkanes ( C1. to C4 ) are gases, C5 to C17 are liquid & higher alkanes C18 onwards are solid.
3) ALKANES are insoluble in water but dissolve in non-polar solvents like benzene, ether, chloroform, etc.
4) the branched chain alkanes have lower boiling point than straight chain alkanes. As the branches in alkanes increase, the boiling point lowers, because then the surface area decrease results in weaker intermolecular forces.
2) except ethylene, all other Alkenes are colourless & odourless. ethylene is a colourless gas with sickly sweet Odour.
3) they are insoluble in water but quite soluble in organic solvents like benzene, ether, chloroform, etc.
4) boiling point of Alkenes increase with increase with increase in molecular mass. A rise of 20 to 30 degree is observed for each added carbon atom.
5) as in Alkanes, Alkenes with branching lowers boiling point.
ALKANES Properties ::
1)alkanes are colourless & odourless.
2) at room temperature, first four alkanes ( C1. to C4 ) are gases, C5 to C17 are liquid & higher alkanes C18 onwards are solid.
3) ALKANES are insoluble in water but dissolve in non-polar solvents like benzene, ether, chloroform, etc.
4) the branched chain alkanes have lower boiling point than straight chain alkanes. As the branches in alkanes increase, the boiling point lowers, because then the surface area decrease results in weaker intermolecular forces.
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By adding cold dilute Baeyer's reagnant
More about Baeyer's Reagnant.
- Baeyer's reagnant is cold dilute
- It is an oxidising agent.
If this mixture is added to an unsaturated compounds such as alkenes or alkanes then :
- Purple colour of changes .
- It is first converted to a green compound which is unstable in alkaline medium.
- This again changes to brown
- The supernatant liquid gets decolourised.
However saturated compounds do not respond to the above test.
In simple words........... your answer is :
In order to test unsaturation first add cold dilute Baeyer's reagnant.
If the reagnant decolorises from purple to colourless then the compound is unsaturated
Otherwise if the reaction does not occur , then it is a saturated compound.
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