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iGCSE 2012 Chemistry Discussion

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Reply 40
Original post by studentno666
Can someone please post the main points which would come up for sure?
Chemistry is my weak subject :frown:


do all the past papers starting from 2008 upto now....U'll fell that its really easy!!
Reply 41
Original post by Big-Daddy
Making CO2, oxygen or hydrogen? Since when is any of that on the syllabus?

I'm aware you need to know H2O2's reaction to form water and oxygen, but would you really say that you "make" oxygen through that reaction? And how do you "make" hydrogen?


to make hydrogen u need to have hydrogen peroxide and then add manganese (IV) oxide which acts as a catalyst...
Reply 42
can anyone give me a detailed answer on how fractions are obtained by fractional distillation of crude oil??
(4 mark detailed answer)
Reply 43
Original post by nithpriya
can anyone give me a detailed answer on how fractions are obtained by fractional distillation of crude oil??
(4 mark detailed answer)


The crude oil is fed in a vaporised form into the fractionating column. The heavier fractions (eg bitumen) immediately condense and sink to the bottom and the lighter fractions like gasoline rise to the top of the column as they are less dense. They are then fractioned off according to their boiling points as they all have different boiling points which allows them to be separated in the column. The fractions are then used for different purposes but some may be cracked to form more useful fractions.

Hope that helped somewhat.


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Reply 44
Original post by Graceyfave
The crude oil is fed in a vaporised form into the fractionating column. The heavier fractions (eg bitumen) immediately condense and sink to the bottom and the lighter fractions like gasoline rise to the top of the column as they are less dense. They are then fractioned off according to their boiling points as they all have different boiling points which allows them to be separated in the column. The fractions are then used for different purposes but some may be cracked to form more useful fractions.

Hope that helped somewhat.


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thanx helped a lot
Reply 45
hey everyone hows chemistry studies coming along?
I'm fed up of studies cant believe there are more to come(a/l, college). Gotto go back to studying. :ciao:

My major question

-When will all studies end?-:confused:
Reply 46
Original post by Big-Daddy
Making CO2, oxygen or hydrogen? Since when is any of that on the syllabus?

I'm aware you need to know H2O2's reaction to form water and oxygen, but would you really say that you "make" oxygen through that reaction? And how do you "make" hydrogen?


BigDaddy we need to know the experiment for evolution of carbon dioxide and oxygen and come one you must know ONE experiment for evolution of hydrogen?
Reply 47
Original post by sahajkaur
BigDaddy we need to know the experiment for evolution of carbon dioxide and oxygen and come one you must know ONE experiment for evolution of hydrogen?


Could you post the experiments? :wink:


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Reply 48
Reply 49
Original post by Graceyfave
Could you post the experiments? :wink:


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For Carbon dioxide just add HCl to any carbonate (most commonly calcium) and it can be collected over water or downward delivery.
For Oxygen Manganese dioxide is the catalyst and Hydrogen peroxide decomposes slowly to form oxygen and water.

For hydrogen just react a metal with an acid :smile:
Reply 50
Original post by sahajkaur
For Carbon dioxide just add HCl to any carbonate (most commonly calcium) and it can be collected over water or downward delivery.
For Oxygen Manganese dioxide is the catalyst and Hydrogen peroxide decomposes slowly to form oxygen and water.

For hydrogen just react a metal with an acid :smile:


You are a god hahah. I don't have to search madly through my notes now!


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Reply 51
Original post by Graceyfave
You are a god hahah. I don't have to search madly through my notes now!


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for physics do you know the advantages and disadvantages of using different energy sources? :frown:( i dont have it in my notes
Reply 52
Hello! Was just looking through the spec and there was a point that I'm not really sure about. It's in bold though, so will only show up on the 1hour paper! It's "evaluate the factors relevant to the choice of method used in the manufacture of ethanol, for example the relative availability of sugar cane and crude oil." Please, anyone know what information we need to know regarding this?


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Reply 53
Original post by sahajkaur
for physics do you know the advantages and disadvantages of using different energy sources? :frown:( i dont have it in my notes


Go to the link below

http://wiki.answers.com/Q/What_are_the_advantages_and_disadvantages_of_renewable_and_non-renewable_energy_sources

Hope it helps!! :wink:
Reply 54
Original post by _ashT
Hello! Was just looking through the spec and there was a point that I'm not really sure about. It's in bold though, so will only show up on the 1hour paper! It's "evaluate the factors relevant to the choice of method used in the manufacture of ethanol, for example the relative availability of sugar cane and crude oil." Please, anyone know what information we need to know regarding this?


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I think it means what are the advantages and disadvantages of different methods to make ethanol.

And what method to use at different countries. eg a country with good climate for growing sugar crops could use fermentation, and a country with plenty of crude oil could use hydration of ethene.
Reply 55
Original post by nithpriya
I think it means what are the advantages and disadvantages of different methods to make ethanol.

And what method to use at different countries. eg a country with good climate for growing sugar crops could use fermentation, and a country with plenty of crude oil could use hydration of ethene.


ah okay, thank you so much! Also, there's another point that I'm not too sure of: "explain how the methods of extraction of the metals in this section are related to their positions in the reactivity series."?


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Reply 56


these are amazing!
Reply 57
Original post by l-g
these are amazing!


thnx but found them too late!
wish i had them earlier
Reply 58
Hi all, does anyone have the name of the guy who does chemistry videos that someone has been posting? I can't find the link :frown: like Alex something? Thanks!


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Reply 59
Original post by Graceyfave
Hi all, does anyone have the name of the guy who does chemistry videos that someone has been posting? I can't find the link :frown: like Alex something? Thanks!


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I have a physics person not chem :/

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