Reactions of Alkanes (1 Viewer)

[mazza_728]

Referring to Question 5 (a and b) page 8 Conquering Chemistry.

Hi guys,
Im just starting year 12 and ive been working ahead. The only thing I dont understand so far is these questions:

When ethane is reacted with bromine in the presence of UV light under certain conditions compounds having 2 Br atoms per molecule are formed. Draw structures to show such compounds are possible.

Under other conditions compounds in three Br atoms per molecule are possible. How many isomers with three Br atoms are possible?

The answers are:

a) Br-CH2-CH2-Br
Br-CH-CH3
Br

b) Two; CBr3-CH3
and
CHBr2-CH2Br

I DONT UNDERSTAND

In the first question where are the other Hydrogens going?
In the second question where are the other hydrogens going and where did the bromines come from? I thought it was only Br2??
HELP!

 

[chunder]

technically talking.....both your answers are wrong because they are considering non-polar Br. In the lab you actually use a polar solution of Bromine Water.

If you don't understand just keep reading and summarising and ask your teacher next term. The chemistry syllabus isn't exactly hard and in reality it isn't even really about chemistry. For some reason there is this overwhelming obsession with the relationship between chemistry - society - Australia. You would be better off spending this holidays finding out more about Alan Walsh, and other prominent Australian scientists...and practice your essay writing skills....my trial had 5 mini essays each worth between 4 and 6 marks.

 

[spice girl]

huh???

the question is prolly asking for all the isomers to
a) di-bromo-ethane
b) tri-bromo-ethane

and they're not asking for complete reaction equations...

 

[+:: $i[Q]u3 ::+]

dont worry about the bromine water bit.. i've gotten away with using br2.
and yes, follow chunder's advice- the chemistry itself doens't get much harder during yr 12.. there aren't a lot more equations, just a few new reactions here and there.
the real hard bit is learning all the society crap. =P
find the syllabus and u'll see what we mean =P

 

[mitochondria]

hehee.. i think i get you confusion.. mazza, this particular question focuses on the products that are of concern but nothing else. If you are to write equations for this you will get hydrogen molecules.. so i take it you understand the isomers bit and i won't go into the details of it:

a) C2H6 + Br2 ---> Br2C2H4 + H2

so in the first part of the question, hydeogen is evolved as a gas

b) 2C2H6 + 3Br2 ---> 2Br3C2H3 + 3H2

so hydrogen is still a gas they don't go anywhere but just released as a gas. It might also be helpful to note that this kind of reaction is called substitution reaction (in this case 2 or 3 Hs are subsituted by 2 or 3 Brs and hydrogen is produced as a result of the subsitution)

so for (a) my answer to you is: 2 hydrogen atoms are released as a H2 molecule

and for (b): 2 of the hydrogen will be resleased as a H2 molecule, the other H will combine with another "loner H" produced else where..

i hope that helps good luck!


p.s. don't forget about the Advice Line

Originally posted by chunder
technically talking.....both your answers are wrong because they are considering non-polar Br. In the lab you actually use a polar solution of Bromine Water.

umm.. what do you mean by "a polar solution of Bromine Water"? and how does non-polar Br differ from polar Br? Thanks in advance.

 

[t-i-m-m-y]

eh... people working ahead- i don't get it and hsc is in 2 weeks

 

[FLR-IT]

Originally posted by t-i-m-m-y
eh... people working ahead- i don't get it and hsc is in 2 weeks

ahahaha ur brain is obviously working overtime

the idea that he is in yr 11 ever cross ur mind??