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AS Chemistry- helping each other out!

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Original post by annie79
thank you thank you thank youuuuuu!!! Im learning so much in one evening, this is great XD


Hahaha np :top:

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when bromine water (Br-OH) is added to an alkene, is it the Br or OH that is the nucleophile in the mechanism for the reaction?
Original post by annie79
when bromine water (Br-OH) is added to an alkene, is it the Br or OH that is the nucleophile in the mechanism for the reaction?


When bromine water is added to alkene electrophilic addition occurs so it is electrophile. You're prob confusing with sodium hydroxide and halogenoalkane thing


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Original post by C0balt
When bromine water is added to alkene electrophilic addition occurs so it is electrophile. You're prob confusing with sodium hydroxide and halogenoalkane thing


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But the OH- donates a pair of electrons to the carbocation..so itsnt the OH- classed as a nucleophile?
Original post by annie79
But the OH- donates a pair of electrons to the carbocation..so itsnt the OH- classed as a nucleophile?


Hm yeah true
It is a weird question asking for nucleophile in electrophilic addition though :hmmm:

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Original post by annie79
when bromine water (Br-OH) is added to an alkene, is it the Br or OH that is the nucleophile in the mechanism for the reaction?


Bromine water is just Br2, there's no hydroxide group
Original post by Joshthemathmo
Bromine water is just Br2, there's no hydroxide group


No Br2 is different, with bromine water you form a bromoalcohol
Original post by Joshthemathmo
Bromine water is just Br2, there's no hydroxide group


Br2+H2O->BrOH+HBr

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Original post by frozo123
No Br2 is different, with bromine water you form a bromoalcohol


Never heard of that, but sounds cool :colone:
Original post by Joshthemathmo
Never heard of that, but sounds cool :colone:


It's basically because the :OH group reacts preferentially to the :Br.
You must have heard of the term bromoalcohol? It's surely on your syllabus? It's just the general name for a halogenoalkane (in this case a bromoalkane with OH groups attached)
Original post by annie79
when bromine water (Br-OH) is added to an alkene, is it the Br or OH that is the nucleophile in the mechanism for the reaction?


Original post by C0balt
When bromine water is added to alkene electrophilic addition occurs so it is electrophile. You're prob confusing with sodium hydroxide and halogenoalkane thing


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Original post by annie79
But the OH- donates a pair of electrons to the carbocation..so itsnt the OH- classed as a nucleophile?


Original post by C0balt
Hm yeah true
It is a weird question asking for nucleophile in electrophilic addition though :hmmm:

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Original post by Joshthemathmo
Bromine water is just Br2, there's no hydroxide group


Original post by frozo123
No Br2 is different, with bromine water you form a bromoalcohol


Original post by C0balt
Br2+H2O->BrOH+HBr

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Original post by Joshthemathmo
Never heard of that, but sounds cool :colone:


Saw you guys were a bit confused... One of the above posters are right, Br2(aq) is bromine water, Br-OH? Nope

I've drawn the mechanism below and am pretty certain it's right, this stuff comes up in A2 too

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Original post by RagaZ
Saw you guys were a bit confused... One of the above posters are right, Br2(aq) is bromine water, Br-OH? Nope

I've drawn the mechanism below and am pretty certain it's right, this stuff comes up in A2 too

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Nahh mate, in bromine water, the concentration of H20 molecules is greater in proportion than Br2 molecules, hence the secondary carbocation has a greater chance reacting with the H20 than the Br-

How you finding A2? Unit 5 is long
Original post by frozo123
Nahh mate, in bromine water, the concentration of H20 molecules is greater in proportion than Br2 molecules, hence the secondary carbocation has a greater chance reacting with the H20 than the Br-

How you finding A2? Unit 5 is long


ahh right! i actually get it now,
http://www.chemguide.co.uk/organicprops/alkenes/halogenation.html (scroll down to see it explained)ok thanks my mistake

and actually its going pretty ok, just anxious to get it over and done with tbh
Original post by RagaZ
Saw you guys were a bit confused... One of the above posters are right, Br2(aq) is bromine water, Br-OH? Nope

I've drawn the mechanism below and am pretty certain it's right, this stuff comes up in A2 too

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Well I would like to believe that chemguide, other random sites out there, and my experienced teacher are right.


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Original post by RagaZ
ahh right! i actually get it now,
http://www.chemguide.co.uk/organicprops/alkenes/halogenation.html (scroll down to see it explained)ok thanks my mistake

and actually its going pretty ok, just anxious to get it over and done with tbh


tbh I don't even know what to expect, lets hope for the best haha
Original post by gabby07
It's basically because the :OH group reacts preferentially to the :Br.
You must have heard of the term bromoalcohol? It's surely on your syllabus? It's just the general name for a halogenoalkane (in this case a bromoalkane with OH groups attached)


I've heard of the compound but i've not encountered that mechanism! I'm on AQA by the way
Original post by Joshthemathmo
I've heard of the compound but i've not encountered that mechanism! I'm on AQA by the way


Ah I see!! You know now :wink:
Hey guys I'm stuck on this one question.

The fuel tank of one type of hydrogen-powered car holds 70kg of magnesiumhydride. Calculate the volume of hydrogen gas, measured at room temperature and pressure,which would be produced if this amount of magnesium hydride reacted with water.

MgH2(s) + 2H2O(I) -----> Mg(OH)2(s) + 2H2(g)


The marking scheme says this :

Moles MgH2 = 70000 = 2659.6 (2660) (1)

26.32Moles H2 = 5319.2 (5320) (1) I've gotten to here, but I just cant figure out what to do to get the next answer.

Volume H2 = 1.28 × 105dm3(1)


Thanks for any help!
Reply 2518
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SSD07
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can someone explain geological and archaeological dating please? like in a lot of depth so i have full detail in case a question comes up. Thanks
Reply 2519
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SSD07
3
also what are the benefits and risks of using radioactive tracers?

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