bromine substitute prac

Request or contribute your recipes here. You can also try doing a search, as there are some old recipe posts which have not or cannot be moved over to this forum.
Post Reply
mtg
Posts: 510
Joined: 15 Aug 2011, 10:48
Job Title: Lab Tech
School: NDSC
Suburb: west gippsland
State/Location: VIC

bromine substitute prac

Post by mtg »

I recall using iodine in cyclohexane and cyclohexene or vice versa for the prac that used to use bromine but I cant remember the exact prac and the theory. Thus I cant find my notes! Cyclohexane has a purple reaction which has confused the teacher.
User avatar
Louise
Posts: 45
Joined: 13 Jun 2006, 10:00
State/Location: NSW

Re: bromine substitute prac

Post by Louise »

You can use acidified potassium permanganate.
In brief

Acidified potassium permanganate solution can be used to differentiate between alkanes and alkenes. Alkenes will react with potassium permanganate solution in the presence of sulfuric acid while alkanes will not. During the reaction with an alkene the permanganate ions (MnO4-) are reduced to manganese (II) ions (Mn2+), resulting in the purple solution becoming colourless, while the alkene is oxidized to a diol.

Preparation of acidified potassium permanganate: Students can prepare their own acidified potassium permanganate solution by adding 2 mL of 0.01 M aqueous potassium permanganate solution to a test tube followed by 1 mL of 2 M sulfuric acid. Then use 1 mL of the acidified potassium permanganate solution to react with 1mL of the alkane or alkene
mtg
Posts: 510
Joined: 15 Aug 2011, 10:48
Job Title: Lab Tech
School: NDSC
Suburb: west gippsland
State/Location: VIC

Re: bromine substitute prac

Post by mtg »

Thank you!!!.
I put Iodine soln in 2 test tubes and cychlohexane and cychlohexene into one each and gently mixed. The Iodine soln, separates out and sinks, and the solution on the top of the cychlohexene one becomes clear while the cychlohexane one separates out and is dark purple. And a tiny crystal of Iodine into each of those chemicals in a separate rack. Cychlohexene went colourless and the cychlohexane purple. But I couldn't explain why it turns purple. Other than just Iodine absorbing yellow light and thus looking purple.
I found your prac but didn't read it properly. Now I will show the chem teacher and my brain will stop hurting!!!
Post Reply