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iGCSE 2012 Chemistry Discussion

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Reply 580
Avatar for g_l
g_l
what do you think will come up on Tuesdays exam?
According to the spec:
Moles calculations
Ionic Compounds (e.g. NaCl)
Covalent substances (diamonds, graphite)
Electrolysis
Ethanol
Endo/Exothermic reactions
Polymers, polymerisation
Contact Process-Sulphuric Acid
Ionic Equations (half equation at cathode/anode, etc)
NaOH-making soaps, etc.

Do you think extraction of Aluminium will come up? How about Haber Process?
What calculations to look out for?
Anyone? :smile:
Hello once again guys. I just went through the specification and i have some questions . If anyone can answer them , i would me more that happy !

1) According to the specification , we have to know how to draw a simple structure of sodium chloride, showing the positions of the NA+ and CL- ions. How can we do this ?

2) Also , it says that we have to know a use for diamond and graphite, and support it .
Can we say that diamond is used to cut stone and concrete, since it is hard , with a high melting and boiling point, and that graphite is used as a dry lubricant, because it is slippery, and its layers can be easily flaked off, since the intermolecular forces of attraction are very weak , and need low energy to be broken down ?
Original post by g_l
what do you think will come up on Tuesdays exam?
According to the spec:
Moles calculations
Ionic Compounds (e.g. NaCl)
Covalent substances (diamonds, graphite)
Electrolysis
Ethanol
Endo/Exothermic reactions
Polymers, polymerisation
Contact Process-Sulphuric Acid
Ionic Equations (half equation at cathode/anode, etc)
NaOH-making soaps, etc.

Do you think extraction of Aluminium will come up? How about Haber Process?
What calculations to look out for?
Anyone? :smile:


I suggest to have a look at the electrolysis calculations, and perhaps at the titration ones? The extraction of aluminium, as well as iron in the blast furnace might come . Also , check the Haber process, and the contact process. Finally , have a look at the dynamic equilibrium chapter, and giant ionic and giant covalent structures, and end your revision by revising the specification , by placing a tick next to the points that you know, and circle the ones that you need to have a look once more , and you shall be just fine. Good Luck ! :smile:
Reply 583
Avatar for member963009
member963009
OP
Original post by Coco406
I don't think it turns reddish-brown because bromine LIQUID is not formed, bromine SOLUTION is formed so it would surely be yellow-orange?



Original post by Sub150
Where did the water come from for the creation of Bromine water??? If Cl gas is added to a Halogenic soln. it doesn't react to make water?? Besides, you dont need to worry about reddish/brown or yellow brown... Just write browny colour... and yes, that is the test for alkenes


No Bromine is evolved which DISSOLVES in the water thus making it orange. Brown would be marked wrong. I've checked this with a teacher, accept it; dont hate. :P
Original post by Coco406
Bromine water is produced (bromine aq)... not liquid bromine
If it said bromine (l) then it would be reddish-brown, but it said (aq) and the test for alkenes is that they decolorise yellow-orange bromine water.

I'm pretty sure that that's right?


No it was bromine gas in the NaCl solution as chlorine had just displaced bromine. So it's reddish-brown.
Reply 585
Avatar for member963009
member963009
OP
Original post by Big-Daddy
No it was bromine gas in the NaCl solution as chlorine had just displaced bromine. So it's reddish-brown.


you wouldnt get the mark if said reddish brown because thats the colour of bromine water, AQUEOUS bromine always has to be orange/yellow. Sorry I've seen it on too many past paper mark schemes 'Orange/Yellow -Reject Red or Brown'
Reply 586
Avatar for bob12321
bob12321
Original post by nithpriya
where can you get 2011 igcse grade boundaries for all subjects?


Hi, I am on my iPod which is why I cant get you a link...

If you type Edexcel Grade Boundaries and go to their website and then control-f international - you will find the June 2011 grade boundaries (chemistry was 140 out of 180 by the way)

^ I checked because I know I lost 12 marks in the last Chem exam!


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Reply 587
Avatar for IGCSE
IGCSE
what do you think will come up in the next paper?
Reply 588
Avatar for g_l
g_l
Help me please
HBr + NaOH => NaBr + H2O
Please explain, in terms of ions, why this is a neutralisation reaction.
Original post by g_l
Help me please
HBr + NaOH => NaBr + H2O
Please explain, in terms of ions, why this is a neutralisation reaction.


HBR contains H+ ion which is reponsible for the acidity of the solution. NaOH contains the OH- ion which is responsible for the alkalinity of a solution. When the two react, they form water where the concentration of the H+ ions and OH- ions are the same; meaning that the solution is neutral. Therefore it is a neutralization reaction.
Reply 590
Avatar for g_l
g_l
Original post by relaxedexams
hbr contains h+ ion which is reponsible for the acidity of the solution. Naoh contains the oh- ion which is responsible for the alkalinity of a solution. When the two react, they form water where the concentration of the h+ ions and oh- ions are the same; meaning that the solution is neutral. Therefore it is a neutralization reaction.


thanks a bunch <3
Sad thing is in the PastPaper, it is only a 1 mark question :frown:
With 4 lines for writing -.-
(edited 11 years ago)
Original post by g_l
thanks a bunch <3
Sad thing is in the PastPaper, it is only a 1 mark question :frown:
With 4 lines for writing -.-


For 1 mark, you can just write that when the reaction takes place, H+ ions and OH- ions react to form water where the concentration of these two ions is the same; making it a neutralization reaction.
Original post by pouloukos
That graphite is used as a dry lubricant, because it is slippery, and its layers can be easily flaked off, since the intermolecular forces of attraction are very weak , and need low energy to be broken down ?


There arent intermolecular attractions in graphite. Graphite is a giant covalant substance. It doesn't have intermolecular forces. If it it, it would have a much lower melting and boiling point! I think you mean the attractions between two layers?
Original post by Relaxedexams
There arent intermolecular attractions in graphite. Graphite is a giant covalant substance. It doesn't have intermolecular forces. If it it, it would have a much lower melting and boiling point! I think you mean the attractions between two layers?


The attraction between the layers are intermolecular attractions. They are very weak. You better revise this again and stop spending time here. Or you can start reading these;
http://answers.yahoo.com/question/index?qid=20100402220652AA92Fi8

http://chemistrybook.hubpages.com/hub/Van-der-Waals-Forces-Hydrogen-Bonds-and-Dipole-dipole
i think paper 2 ought to be easy cuz its only an hour!!
im tryin my best to get around 50's then its a definite A*!! :smile:
Original post by Relaxedexams
There arent intermolecular attractions in graphite. Graphite is a giant covalant substance. It doesn't have intermolecular forces. If it it, it would have a much lower melting and boiling point! I think you mean the attractions between two layers?


What???
this is wrong! Stop confusing me!
Graphite is a giant covalent structure and is an allotrope of carbon. Unlike diamond it if formed in 2D layers and does contain weak intermolecular forces. But as it is a giant covalent structure to sublime it you not only need to bread the weak intermolecular forces but the covalent bonds as well..
Reply 597
Avatar for Sub150
Sub150
Original post by (◕ ‿ ▒r▀▀
Graphite is a giant covalent structure and is an allotrope of carbon. Unlike diamond it if formed in 2D layers and does contain weak intermolecular forces. But as it is a giant covalent structure to sublime it you not only need to bread the weak intermolecular forces but the covalent bonds as well..


Graphite is giant covalent... There is one delocalised electron, hence the conductivity and the lubrication; te attraction between layers is lowered as a result of this. It's not 2d... And I'm not sure if it contains intermolecular forces


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Original post by Sub150
Graphite is giant covalent... There is one delocalised electron, hence the conductivity and the lubrication; te attraction between layers is lowered as a result of this. It's not 2d... And I'm not sure if it contains intermolecular forces


This was posted from The Student Room's iPhone/iPad App


You're wrong. Don't confuse people...little knowledge is dangerous...
1. It's lubrication is not a direct nor an indirect result of it having delocalised electrons.
2.It is a giant molecule that continues in 2D ie it layers are on one plane
3.It does contain intermolecular forces. Then what do you call the weaf forces between the layers? Van-de-wall forces? van-de-wall forces are also a type of intermolecular attractions!

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