January 2011-OCR Chemistry F322

Watch this thread
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report Thread starter 7 years ago
#1
For 1bii why does it say, IGNORE cyclohexane increases volatility of fuel IGNORE cyclohexane has a lower boiling point ?
and for 1cii, why is 'reaction is difficult to control is NOT sufficient' and on the examiner's report it says Candidates found (ii) very demanding and often referred to the toxic nature of chlorine or the danger of radicals, neither of which were given credit in the mark scheme. . why?
for 4d, why does it say
IGNORE less pollution- pollution is mentioned in the question
for 7c why is Destroys habitats is NOT sufficient
0
reply
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report Thread starter 7 years ago
#2
(Original post by runny4)
For 1bii why does it say, IGNORE cyclohexane increases volatility of fuel IGNORE cyclohexane has a lower boiling point ?
and for 1cii, why is 'reaction is difficult to control is NOT sufficient' and on the examiner's report it says Candidates found (ii) very demanding and often referred to the toxic nature of chlorine or the danger of radicals, neither of which were given credit in the mark scheme. . why?
for 4d, why does it say
IGNORE less pollution- pollution is mentioned in the question
for 7c why is Destroys habitats is NOT sufficient
this
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#3
Report 7 years ago
#3
They don't process hexane to make it boil more easily, they do it to make it burn more efficiently (and make H2). They wouldn't want it to boil more easily, it would be difficult to store etc.

The Q was about preparation of chlorocyclohexane, rather than about radical substitution reactions generally. "If you wanted to make chlorocyclohexane, this isn't the method you'd use, why not?" would have been a more (too?) direct way of asking it.
Less pollution is faaar too vague. Do you mean air pollution? water pollution? noise pollution?

I don't much like 7c, especially since the spec. says: 2.4.2(b) explain that the apparent benefits may be offset by unexpected and detrimental side effects; Examples for (b) (not examinable): Production of biodiesel uses grain crops and land needed for food, with poorer countries being worse affected.
0
reply
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#4
Report Thread starter 7 years ago
#4
(Original post by Pigster)
They don't process hexane to make it boil more easily, they do it to make it burn more efficiently (and make H2). They wouldn't want it to boil more easily, it would be difficult to store etc.

The Q was about preparation of chlorocyclohexane, rather than about radical substitution reactions generally. "If you wanted to make chlorocyclohexane, this isn't the method you'd use, why not?" would have been a more (too?) direct way of asking it.
Less pollution is faaar too vague. Do you mean air pollution? water pollution? noise pollution?

I don't much like 7c, especially since the spec. says: 2.4.2(b) [/font][/font][/font][/font][/font][/font]
but if wanted to make chlorocyclohexane wouldn't u want it to be so u could control its production?
and what advice would u give for 7c.
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#5
Report 7 years ago
#5
If I was wanting to make some chlorocyclohexane, I'd start with cyclohexene and add HCl. That way, I'd make pretty much pure chlorocyclohexane (and I wouldn't explode whilst making it).

If I wanted to make some chlorocyclohexane mixed in with all sorts of other chemicals, e.g. 1,1-dichloro, 1,2-, 1,3- 1,4-, 1,1,2-tri etc. etc. etc. then I'd use radical substitution.
0
reply
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#6
Report Thread starter 7 years ago
#6
(Original post by Pigster)
If I was wanting to make some chlorocyclohexane, I'd start with cyclohexene and add HCl. That way, I'd make pretty much pure chlorocyclohexane (and I wouldn't explode whilst making it).

If I wanted to make some chlorocyclohexane mixed in with all sorts of other chemicals, e.g. 1,1-dichloro, 1,2-, 1,3- 1,4-, 1,1,2-tri etc. etc. etc. then I'd use radical substitution.
Why wouldn't u get a mark for referring to the toxic nature of chlorine or the danger of radicals? see examiners report
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#7
Report 7 years ago
#7
I can't say for certain, but I'd bet it was the wording: "one problem of using this reaction" as in a radical substitution reaction as opposed to an electrophilic substitution reaction, which could also be used to "prepare a sample of chlorocyclohexane."
0
reply
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#8
Report Thread starter 7 years ago
#8
(Original post by Pigster)
I can't say for certain, but I'd bet it was the wording: "one problem of using this reaction" as in a radical substitution reaction as opposed to an electrophilic substitution reaction, which could also be used to "prepare a sample of chlorocyclohexane."
but electrophilic addition doesn't involve radicals so surely u could talk about them and the fact that this reaction is so difficult to control that its dangerous
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#9
Report 7 years ago
#9
At our school, we mix cyclohexane with chlorine water and leave it on the windowsill (in the summer). The fact that there are loads of Cl radicals in a beaker on the windowsill in the classroom we're in isn't a problem. Nor is the toxic chlorine in said beakers.

If we were setting out to make chlorocyclohexane, then choosing this reaction would be a problem, as my yield would be low and my atom economy would be terrible (what with all the other products).
0
reply
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#10
Report Thread starter 7 years ago
#10
(Original post by Pigster)
At our school, we mix cyclohexane with chlorine water and leave it on the windowsill (in the summer). The fact that there are loads of Cl radicals in a beaker on the windowsill in the classroom we're in isn't a problem. Nor is the toxic chlorine in said beakers.

If we were setting out to make chlorocyclohexane, then choosing this reaction would be a problem, as my yield would be low and my atom economy would be terrible (what with all the other products).
oh so the thing about it being difficult control is referring to the products made being difficult to control and it is too vague to day that and the chlorine radicals are only dangerous if u make it outside as then they can attack the ozone layer but if u make it inside then there is no danger from chlorine radicals.

but then why is it sometimes said that radical substitution reactions are so quick that they can cause explosions?- like u said in one of your responses earlier
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#11
Report 7 years ago
#11
The term difficulty to control is indeed referring to the lack of control over what you would make, i.e. there would be lots of different products.

Cl radicals produced at ground level would react with something long before they were able to reach the ozone layer (although they could get involved in ozone formation at ground level and smog). It isn't that they're safe inside, they are not. I was just pointing out that the radical substitution reaction can be done safely in a classroom. If you were to mix a gaseous alkane and chlorine and start the reaction then it would be explosive. We don't - for that reason - instead, we do the chemistry in solution so that concentrations and therefore rates are lower.
0
reply
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#12
Report Thread starter 7 years ago
#12
(Original post by Pigster)
The term difficulty to control is indeed referring to the lack of control over what you would make, i.e. there would be lots of different products.

Cl radicals produced at ground level would react with something long before they were able to reach the ozone layer (although they could get involved in ozone formation at ground level and smog). It isn't that they're safe inside, they are not. I was just pointing out that the radical substitution reaction can be done safely in a classroom. If you were to mix a gaseous alkane and chlorine and start the reaction then it would be explosive. We don't - for that reason - instead, we do the chemistry in solution so that concentrations and therefore rates are lower.
so are gaseous alkanes reacting with cl radicals are only dangerous?

and if cl radicals react with stuff to form ground level ozone which is bad for health shouldn't that get a mark?- or are there some special controlled conditions that stop them from escaping that u just have to assume.
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#13
Report 7 years ago
#13
Whether it is dangerous depends on concentrations and quantities.

In practice, radical substitution reactions create as many radicals (initiation) as are used up (termination). There should be (next to) no radicals left over once the reaction finishes.

There are other ground level reactions of radicals, esp. involving water (of which there is effectively none in the ozone layer, I think) which removes them. In smog, the radicals are constantly being produced (N2+O2 -> 2NO) in car engines. The possibility of a few stray Cl radicals from a radical substitution reaction is such a small contributor, it can effectively be ignored.
0
reply
runny4
Badges: 6
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#14
Report Thread starter 7 years ago
#14
(Original post by Pigster)
Whether it is dangerous depends on concentrations and quantities.

In practice, radical substitution reactions create as many radicals (initiation) as are used up (termination). There should be (next to) no radicals left over once the reaction finishes.

There are other ground level reactions of radicals, esp. involving water (of which there is effectively none in the ozone layer, I think) which removes them. In smog, the radicals are constantly being produced (N2+O2 -> 2NO) in car engines. The possibility of a few stray Cl radicals from a radical substitution reaction is such a small contributor, it can effectively be ignored.
then why from cfc's are cl radicals dangerous to the ozone layer shouldn't they be effectively be used up on the ground?
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#15
Report 7 years ago
#15
CFCs were released at ground level, they took decades to travel up through the atmosphere where they are exposed to u.v. producing Cl radicals high in the atmosphere. If a CFC molecule was split at ground level, the Cl produced would be 'used up' rather quickly (wot wiv all da water down here).
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest

How did The Student Room help you with your university application?

Talking to current university students (8)
24.24%
Talking to peers going through the same thing (10)
30.3%
Speaking to student ambassadors from the universities (2)
6.06%
Speaking to staff members from universities (0)
0%
Using the personal statement builder, library or helper service (3)
9.09%
Reading articles about what steps to take (6)
18.18%
Learning about/speaking to Student Finance England (2)
6.06%
Something else (tell us in the thread) (2)
6.06%

Watched Threads

View All