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January 2011-OCR Chemistry F322
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runny4
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#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
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
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runny4
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#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
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
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Pigster
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#3
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#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.
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.
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runny4
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#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]
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]
and what advice would u give for 7c.
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Pigster
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#5
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#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.
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.
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runny4
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#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.
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.
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Pigster
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#7
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#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."
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runny4
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#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."
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."
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Pigster
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#9
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#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).
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).
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runny4
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#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).
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).
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
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Pigster
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#11
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#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.
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.
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runny4
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#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.
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.
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.
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Pigster
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#13
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#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.
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.
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runny4
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#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.
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.
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Pigster
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#15
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#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).
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