ATAR Notes: Forum
Archived Discussion => Mathematics and Science => 2013 => Exam Discussion => Victoria => Chemistry => Topic started by: thushan on November 12, 2013, 09:59:58 pm
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Here you go. If there's an error just post here.
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Thanks! :)
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You forgot Question 4d
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I have a feeling 6d is incorrect. Combustion reactions are exothermic and so the energy of the products is lower than that of the reactants. Probably just a brief mental blank. :P
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edit: saw your explanation in the other thread
Out of curiosity, for Q5 part D, how do the amounts of ethanoic acid and ethanoate ions become equal? Surely if you've added half the amount of NaOH, half of the acid is going to be neutralised as ethanoate, and a little bit of the remaining acid will also be ionised so there's more than half of the acid present as ethanoate ions? Or are we meant to assume they're equal even though they're not?
Also Q10 bii is balanced wrong - the number of O2 should be 80.
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Also, I think the combustion equation in 8ai is incorrect.
EDIT: I think the combustion equation in 10bii is also incorrect. :S
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OMG lost like 6 marks ! :(
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For 6b, would I lose the mark for writing ethene as CH2CH2 instead of CH2=CH2?
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Top of page 6 should be in Litres
And I'm a bit worried now lol
Nah its mL - density is given in g mL^-1.
And yeah rawr - Q4d - Biomass is derived from recently living plant material, whereas fossil fuels is derived from plant material that has been dead for a long time, whose stores are only very slowly being replenished.
And Stick you're right - will fix. Man I'm so tired. :(
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OMG lost like 6 marks ! :(
I think I lost the same amount. Don't be sad - 114/120 is a great score! :D
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And Stick you're right - will fix. Man I'm so tired. :(
Yeah, it's like your brain... combusted.
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Ha. Ha. Fixed btw - new doc's up.
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Interested to hear your reasoning for question 13 Thush.
Also for 30, I'd have thought the answer would be D, not C. Given that all three solutions are aqueous, there shouldn't be any metal deposited onto the electrode in the solution containing K+ because H2O would be reduced in preference to K+ for an infinitely long amount of time, producing no metal (K+(aq) is never reduced to K(s))
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Interested to hear your reasoning for question 13 Thush.
Also for 30, I'd have thought the answer would be D, not C. Given that all three solutions are aqueous, there shouldn't be any metal deposited onto the electrode in the solution containing K+ because H2O would be reduced in preference to K+ for an infinitely long amount of time, producing no metal.
Frick this.
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Interested to hear your reasoning for question 13 Thush.
Yes, please do explain, because I'm still not following the common solution of B. :S
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Frick this.
Haha mate don't worry, I'm sure your brain has been jellified by med exams in the last few days.
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also 10.bii, I think it should be 80O2, as there's the 6O atoms from the fatty acid
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Yup I fixed that. :D
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Yup I fixed that. :D
And looking at it again, I guess B would make more sense if you looked at the organic compound itself.
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Yup I fixed that. :D
Oh someone already mentioned it *derp*
I think this little lion needs some sleeeep
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Is there meant to be a negative sign for the ∆H value in question 10, since it's combustion?
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Your MC answers are scaring me :(
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Is there meant to be a negative sign for the ∆H value in question 10, since it's combustion?
That too.
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Also, the number of moles of O2 excess is 0.061moles not the original amount in 8aii?
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Oh, I just took it to mean how much of the reactant in excess there is originally.
Guys, I'm sorry from all the mistakes, I've just been extremely tired, I was under the pump these last two weeks with exam prep (and 2nd year med has pretty crazy exam prep with big exams and that :( ). I just finished today.
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For question 9 is it possible to say
Mass spectrum
Molecular ion peak at 88, same mass as CH3COOCH2CH3
Infared
Absorbtion band at 1750, meaning a C=O bond
Proton NMR
3 hydrogen environments, which is true for CH3COOCH2CH3
Also with 7.b, even with the explanation I still don't get why the total mass is 10.3 not 9.445, is it because the sludge stays on the electrode? Because I don't believe it says it was done until no more copper was being deposited so there may have been copper still there, or am I missing the point?
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For question 4, doesn't a decreased volume cause a shift to the left and thus decreased hydrogen yield? (Question 4a ii)
For the next part (iii), would an increased temperature not decrease the reaction rate for Reaction 2 because it is exothermic and thus the back reaction (endothermic) is favoured?
Thanks!
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CH2CH2 should be accepted because there is only one place the double bond can be. Also for the precipitation reaction would they accept my water being on top of the arrow? Am i being pedantic?
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I did the same as Sentar for question 9 - in retrospect, I should have written a bit more :-\
What do you think about the relative simplicity/brevity of those answers? (In your own opinion, of course)
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I did the same as well! Surely they couldn't give you zero for those answers?
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Your MC answers are scaring me :(
Multiple choice answers are freaking me out too!
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Interested to hear your reasoning for question 13 Thush.
Also for 30, I'd have thought the answer would be D, not C. Given that all three solutions are aqueous, there shouldn't be any metal deposited onto the electrode in the solution containing K+ because H2O would be reduced in preference to K+ for an infinitely long amount of time, producing no metal (K+(aq) is never reduced to K(s))
OMG YES. I was so suspicious of the last MC just because they're usually tricky, and I picked up on the K+ all those practice exams didn't go to waste! ;)
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Hey, for qn 30,
is it me or is the answer C? :o
Since the same current is provided, that means n(e-) is the same throughout.
Let's say the charge equivalence of 1mole of n(e-) is supplied,
then 39.1g of K, 0.5(55.9)g of Fe and 107.9g of Ag?
0g of K is produced. This is because the electrolyte containing K+ is aqueous, meaning it contains water. Water is a stronger oxidant than potassium ions are, and since there is an 'infinite' amount of water in aqueous solutions, all of the electrons supplied end up reducing water until they've been exhausted. Thus no K+ ions are reduced to potassium metal.
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Shouldn't there be 55.9/2g of Fe? Because Fe is 2+ therefore n(e-)=2? Kind of thing... And there is no K+ reduced, therefore the answer is potassium ---> iron ----> silver? Which is D.
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Shouldn't there be 55.9/2g of Fe? Because Fe is 2+ therefore n(e-)=2? Kind of thing... And there is no K+ reduced, therefore the answer is potassium ---> iron ----> silver? Which is D.
Exactly! Although you can't calculate the exact mass of Fe, because you don't know what current was used exactly. You only know that the current used for each solution was the same.
According to the respective electron:metal ratios for the reduction of Fe2+ and Ag+ them, you're going to have half the amount of Fe2+ that you do Ag+ holding all else constant. So increasing amount in mole of the three metals is potassium, iron, silver. Since silver is heavier than iron and there is no potassium, in increasing mass it's also potassium, iron, silver.
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what if you wrote C2O42- (aq) + Ca2+ (aq) --> CaC2O4 (s) ...
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For question 4, doesn't a decreased volume cause a shift to the left and thus decreased hydrogen yield? (Question 4a ii)
For the next part (iii), would an increased temperature not decrease the reaction rate for Reaction 2 because it is exothermic and thus the back reaction (endothermic) is favoured?
Thanks!
anyone?
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saraoj, an increase in temperature always increases the rate, regardless if endothermic or exothermic!
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saraoj, an increase in temperature always increases the rate, regardless if endothermic or exothermic!
Too true I started off with a yield explanation, but then shifted towards increase in reaction rate for both once I read the question again!!
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Too true I started off with a yield explanation, but then shifted towards increase in reaction rate for both once I read the question again!!
oh my gosh so many silly mistakes, thanks heaps!
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saraoj, an increase in temperature always increases the rate, regardless if endothermic or exothermic!
For individual reactions, yes, but for anyone who has done the ATAR Notes chemistry exam 4...they'll know what I mean...
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For individual reactions, yes, but for anyone who has done the ATAR Notes chemistry exam 4...they'll know what I mean...
What do you mean? lol
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For that one, an increase in temperature reduced the rate of the overall reaction.
It was a two-step reaction, and the first step was exothermic and very fast, so it reached equilibrium very. Increasing the temperature wouldn't noticeably increase the rate of that reaction, but it reduced the yield. The second step was rather slow, and the rate increase from the temperature arise apparently did not compensate for the lower yield from reaction 1; one of the products in reaction 1 was a reactant in reaction 2. So here, a temperature increase REDUCED the overall rate.
But that was just one of Thushan's troll questions :D
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For that one, an increase in temperature reduced the rate of the overall reaction.
It was a two-step reaction, and the first step was exothermic and very fast, so it reached equilibrium very. Increasing the temperature wouldn't noticeably increase the rate of that reaction, but it reduced the yield. The second step was rather slow, and the rate increase from the temperature arise apparently did not compensate for the lower yield from reaction 1; one of the products in reaction 1 was a reactant in reaction 2. So here, a temperature increase REDUCED the overall rate.
But that was just one of Thushan's troll questions :D
I had reduced for the exothermic one as well.
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I'm a trollface.
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I'm a trollface.
Wait, I'm confused now, is it decreased or increased, lol.
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Increase in temperature increases reaction rate.
In the qn nliu95 was referring to, that reaction in my trial exam is an EXTREMELY UNUSUAL one.
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For Q 4 why can't it be B?
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For question 9 is it possible to say
Mass spectrum
Molecular ion peak at 88, same mass as CH3COOCH2CH3
Infared
Absorbtion band at 1750, meaning a C=O bond
Proton NMR
3 hydrogen environments, which is true for CH3COOCH2CH3
Oh goodness, I wrote exactly the same. I think points 2 and 3 should be OK, but I'm iffy about point 1.
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For Q 4 why can't it be B?
That omits II which is used for a back titration. Eg. CaCO3 solid uses excess HCl, then that excess HCl is titrated with NaOH to determine the HCl reacted as a back titration is volumetric analysis, you can't do it directly if your compound eg. CaCO3 isn't soluble in water to begin with.
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That omits II which is used for a back titration. Eg. CaCO3 solid uses excess HCl, then that excess HCl is titrated with NaOH to determine the HCl reacted as a back titration is volumetric analysis, you can't do it directly if your compound eg. CaCO3 isn't soluble in water to begin with.
Ah good point! thanks :)
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could you say 500 nm?? for question about co2+ ions