iGCSE 2012 Chemistry Discussion
Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.
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Re: iGCSE 2012 Chemistry DiscussionActually, I can't see that this will come up in our exam, as the level of depth is a tiny bit higher than usual, but let's give it a shot anyway.(Original post by Graceyfave)
Can someone clarify electrolysis of aqueous solutions? The difference between concentrated and dilute?
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Basically, some molecules in solution are easier to oxidize than others: take NaCl aqueous solution. Water molecules or Cl- ions can both be produced at the anode, but Cl- ions are easier to oxidize than water molecules, so you'll generally produce more Cl2 gas at the anode: 2Cl- -> Cl2 + 2e-
However, the more dilute the solution (i.e. the higher the concentration of water molecules), the more O2 gas will be coming out as well: 4OH- -> 2H2O + 4e- + O2. So you'll get both, depending on the concentration of the solution.
Hope this helps
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Re: iGCSE 2012 Chemistry DiscussionNot on GCSE syllabus.(Original post by Graceyfave)
Can someone clarify electrolysis of aqueous solutions? The difference between concentrated and dilute?
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Correct but not on our syllabus(Original post by Big-Daddy)
Actually, I can't see that this will come up in our exam, as the level of depth is a tiny bit higher than usual, but let's give it a shot anyway.
Basically, some molecules in solution are easier to oxidize than others: take NaCl aqueous solution. Water molecules or Cl- ions can both be produced at the anode, but Cl- ions are easier to oxidize than water molecules, so you'll generally produce more Cl2 gas at the anode: 2Cl- -> Cl2 + 2e-
However, the more dilute the solution (i.e. the higher the concentration of water molecules), the more O2 gas will be coming out as well: 4OH- -> 2H2O + 4e- + O2. So you'll get both, depending on the concentration of the solution.
Hope this helps
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Re: iGCSE 2012 Chemistry DiscussionI think this is about why Aluminium is extracted by electrolysis whereas Iron is reduced with CO. Aluminium is more reactive than Iron and Carbon is in between them. Hence, Carbon Monoxide can reduced Iron Oxide to Iron. I think that this doesn't work for aluminium though because aluminium is more reactive than carbon, so you need to use electrolysis.(Original post by _ashT)
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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Re: iGCSE 2012 Chemistry Discussiondescribe simple experiments for the electrolysis, using inert electrodes, of aqueous
solutions of sodium chloride, copper(II) sulfate and dilute sulfuric acid and predict
the products
1.54 write ionic half-equations representing the reactions at the electrodes during electrolysis
1.55 recall that one faraday represents one mole of electrons
1.56 calculate the amounts of the products of the electrolysis of molten salts and aqueous
solutions.
describe the manufacture of sodium hydroxide and chlorine by the electrolysis of
concentrated sodium chloride solution (brine) in a diaphragm cell
5.29 write ionic half-equations for the reactions at the electrodes in the diaphragm cell
5.30 recall important uses of sodium hydroxide, including the manufacture of bleach,
paper and soap; and of chlorine, including sterilising water supplies and in the
manufacture of bleach and hydrochloric acid
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Re: iGCSE 2012 Chemistry DiscussionElectrolysis calculations. I never got my head around them - in the end I had to develop an equation to solve them.(Original post by HerroKitty)
Does anyone happen to know which calcualtions only appear on paper 2? -
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Re: iGCSE 2012 Chemistry DiscussionCould you share it please?(Original post by Big-Daddy)
Electrolysis calculations. I never got my head around them - in the end I had to develop an equation to solve them. -
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Re: iGCSE 2012 Chemistry Discussion(Original post by Big-Daddy)
Actually, I can't see that this will come up in our exam, as the level of depth is a tiny bit higher than usual, but let's give it a shot anyway.
Basically, some molecules in solution are easier to oxidize than others: take NaCl aqueous solution. Water molecules or Cl- ions can both be produced at the anode, but Cl- ions are easier to oxidize than water molecules, so you'll generally produce more Cl2 gas at the anode: 2Cl- -> Cl2 + 2e-
However, the more dilute the solution (i.e. the higher the concentration of water molecules), the more O2 gas will be coming out as well: 4OH- -> 2H2O + 4e- + O2. So you'll get both, depending on the concentration of the solution.
Hope this helps
You misunderstood the specification. It is not asking you about the DIFFERENCE between electrolysis of dilute and concentrated products (explained above) but rather it is asking you aout the electrolysis of CONCENTRATED sodium chloride solution which is one of the industrial process we have to know. So study that and please don't mislead others.(Original post by Graceyfave)
Can someone clarify electrolysis of aqueous solutions? The difference between concentrated and dilute?
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Re: iGCSE 2012 Chemistry Discussion' The difference between concentrated and dilute?' isnt and it has never come up, but its easy to work out(Original post by Big-Daddy)
It is in the textbook, so I think it may come up. Unlikely, but possible.
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Re: iGCSE 2012 Chemistry DiscussionIn which hydrogen gas and chlorine gas will be produced.(Original post by sahajkaur)
You misunderstood the specification. It is not asking you about the DIFFERENCE between electrolysis of dilute and concentrated products (explained above) but rather it is asking you aout the electrolysis of CONCENTRATED sodium chloride solution which is one of the industrial process we have to know. So study that and please don't mislead others.
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Sorry to be a pain but could someone please point me in the way of like a revision list or something?
Our teachers gave us one for bio, and it had like: 3.2 know the how to label a diagram of the chest cavity, including thorax, diaphragm etc. I'm presuming it's an official one but not sure 
would be really helpfull if someone could 
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Re: iGCSE 2012 Chemistry Discussionhttp://www.edexcel.com/migrationdocu...0Issue%203.pdf(Original post by the11thJD)
Sorry to be a pain but could someone please point me in the way of like a revision list or something? Our teachers gave us one for bio, and it had like: 3.2 know the how to label a diagram of the chest cavity, including thorax, diaphragm etc. I'm presuming it's an official one but not sure would be really helpfull if someone could
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Re: iGCSE 2012 Chemistry DiscussionOh, you again(Original post by sahajkaur)
Hi guys anyone doing chem igcse out there?
Yes I am
Really should start working...
But yeah 
