4 Comparing Alkanes And Alkenes 2a6r42

Comparing properties of Alkanes and Alkenes Similarities: Properties Solubility in water Solubility in organic solvent Conductivity Boiling and melting point Molecular formula Molecular mass

Alkanes & Alkenes No Yes No Low Each member of homologous differs from the next/successive member by a unit −CH2− Each member of homologous differs from the next/successive member of 14 unit

Differences: Properties

Alkanes

Reaction with oxygen, O2 gas

It burned with less sooty yellow flame

The reddish-brown Reaction with bromine, colour of bromine Br2 water water remains unchanged The purple colour of Reaction with acidified acidified potassium potassium manganate(VII) manganate(VII), solutions remained KMnO4 solution unchanged 1

Alkenes It burned with a more sooty yellow flame The reddishbrown colour of bromine water decolourised The purple colour of acidified potassium manganate(VII) solutions was decolourised

[SPOT SPM QUESTIONS 2011] ESSAY;

A

B

HOW TO IDENTIFY THE ALKANE and ALKENE IN THE BOTTLES? Solutions: i. Substances & Apparatus ii. Procedure iii. Observations iv. Inference [10 marks] Sample answer Aim: To investigate the liquid in bottle A and B Dropper

Test tube

Test tube A

Test tube B

2

Substances & Apparatus; Bromine water , 2 test tubes, 2 dropper Procedure; 1. The apparatus shown above is prepared. 2. 2-5 cm3 bromine water is measured with measuring cylinder 5ml and poured into a test tube. 3. A few drops of liquid from bottle A is put/added with dropper into the test tube, and shake. 4. Observations is recorded. 5. The experiments is repeated by replace the liquid from bottle A with bottle B. Observation and inferences: Test Tube

Observation

Inference

Liquid in bottle A

The reddish-brown colour of bromine water Contains alkane remains unchanged

Liquid in bottle B

The reddish-brown colour of bromine water Contains alkene decolorized

Easylah!

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