edexcel chemistry as help needed here guys :(

[~ Miss Relina ~]

well explain why a metal halide and concentrated sulfuric
acid should not be used when making a bromoalkane or an
iodoalkane???

[elemis]

well explain why a metal halide and concentrated sulfuric
acid should not be used when making a bromoalkane or an
iodoalkane???

Its a very vigorous reaction which can resultbin the acid being 'spat' out at you from the reaction flask.

Its much safer to use PCl5 or PI3 when converting an alcohol to a haloalkane

[Amii]

50% of sulfuric acid is used when preparing bromoalkane as concentrated sulfuric acid will oxidise much of the hydrogen bromide( produced intially) to bromine.

When preparing iodoalkane not even 50 % of sulfuric acid can be used - cause it will completely oxidise the hydrogen iodide.

Hope it helps  

[~ Miss Relina ~]

ok Thanks now i ve other doubt what is the difference between the reaction mechanisms of primary halogenoalkane and secondary halogenoalkane and tertairy  halogenoalkane plz its urgent???
also if the alkyl groups helps to stabilise the halogenoalkane then why the terairy halogenoalkane is the faster in reaction with for examlpe Agcl3 (aq) even it is most one with 3 alkyl groups around it

plzplz plz i am really worried about practicals in chemisrty exams are near and i'm seeking fior yr help plz attach anynotes i've websites but donot know wht is the impotrant to our as-edecel specification
also i'm studying from that blue book of chemistry but i found that i cannot really get what the specification nedds as when i do recent pastpaers i find myself laking of info so do i need other book to revise from and if yes what is it  plz donot froget to reply i'm extremely worried

[Amii]

Primary halogenoalkanes undergo SN2 mechanism.This mechanism involves having 2 species at the beginning and consists of a single step that goes through a transition state.

Tertiary halogenoalkanes undergo SN1 mechanism.It has only 1 species involved at the beginning and takes place in 2 steps.

Secondary halogenoalkanes can undergo both SN1 and SN2 meachanism.

http://www.chemguide.co.uk/mechanisms/nucsub/hydroxidett.html

The weaker the carbon-halogen bond the faster is the reaction.A ethyl group has a tendency to push the electrons away from itself. Since there is a general shift of electrons away from the ethyl group and towards the halogen atom the release of the halide ion becomes easier.Hence fastest reaction with tertiary and slowest with primary halogenoalkanes.

http://www.chemguide.co.uk/mechanisms/eladd/carbonium.html#top
Just read through and check if it helps.

I am sorry but I am not doing the practical written paper - so I don't have any such book for practicals.

Just hold on there will be other members helping you out with that  

[~ Miss Relina ~]

Thanks and waaaaaaaiiiiiiiiiitng for other members

also why bariuum is very diificult to extract from electrolysis??(i think because the ba is so reactive so hard to remove it from the mixture)