Originally posted by TheSpaceManatee:Didn't talk about partially filled 3d orbitals but did mention the rest hope its enough... And I think is to Cu2+ since its +0.34V and less positive than Cu+ half cell +0.52V so preferentially oxidised to Cu2+, not sure though...
And I didn't draw the bonds on in the draw ligand question i.e I didnt draw out the COO as O-C=O, just left it as COO, can?
Originally posted by TheSpaceManatee:Didn't talk about partially filled 3d orbitals but did mention the rest hope its enough... And I think is to Cu2+ since its +0.34V and less positive than Cu+ half cell +0.52V so preferentially oxidised to Cu2+, not sure though...
And I didn't draw the bonds on in the draw ligand question i.e I didnt draw out the COO as O-C=O, just left it as COO, can?
Yeah, tho question asked why copper doesnt react with acid so just show both E cell values <0...
Can of course can, they didnt say full structural formula or anything so long as you show your negative charge with lone pair on O
As for the reactivity question, i think generally the crux lies in the elctrons being more attracted to the nucleus (supported by I.E values), therefore...
may I check what's the answer for qn 1 part 1? the one about MP
Originally posted by captainkidzs:may I check what's the answer for qn 1 part 1? the one about MP
one has hydrogen bond one dont have
the next part one has higher Mr so larger electron cloud bla bla bla..
Originally posted by Thefire521:one has hydrogen bond one dont have
the next part one has higher Mr so larger electron cloud bla bla bla..
Were you able to squeeze ur explaination on 3 lines ? LOL I had to get a new fullscap to write one essay explaining it. Thought I was taking my econs paper for awhile
If I used pencil to draw skeletal formula, mechanism, and structures will I be penalised?
and if I forgot to x2 the Mr of Iodine, how many marks will I lose? my answer was 5.70 which was twice of 2.85. question was 4m.
What is/are the accepted answers for the NO2 + SO2 question and the Cu ligand qn?
Hi! If my pre calculation is wrong, will i still be rewarded marks for explanation?
And for planning is it cannot pipette out 25cm3 of the h2so4 from the conical flask given and carry out exp from there? Becos i did that and my mass was ard 2.1g instead of 4.smth.
I didn't mention about hydrogen bond. I just mention triester is spherical in shape and while the fatty acids aren't so less point of contact for van Der walls. is it possible?
Originally posted by Jlptj:Hi! If my pre calculation is wrong, will i still be rewarded marks for explanation?
And for planning is it cannot pipette out 25cm3 of the h2so4 from the conical flask given and carry out exp from there? Becos i did that and my mass was ard 2.1g instead of 4.smth.
In general for planning (the steps)
1). Do calculation for approx mass (shoud be arond 4+ grams to measure)
2). Measure using TARE function or repeat weighing using weighing bottle and transfer into the H2SO4 flask
3). Swirl, check for end of rxn when ppt dissolve and efferverscence/gas bubble isnt evolved
4). Calculate dilution factor (should be at least 10 times) and take out abit of the solution and dilute in volumetric flask (100/250)
5). Pipette 25 cm3 and titrate against NaOH, record for 2 titre value within 0.1, and take average
6). perform your final calculation to obtain percentage
Ya, in fact they rather you use pencil than use pen and cancel everywhere lol. And the guy who submitted a page of essay for a 2 mark question will only get raged at inside the examiner's report!
@arjoe They didnt ask you for how to shorten carbon chain, in fact the rancid olive oil was exposed to air so how can there be KMNO4 present in the air all of us will die.
I think ultima explained about the mechanism so the equation you can just represent oxidising agent as [O]
@captainkids No, hydrogen bond is probably what they are looking for in the first place since one has ester linkage, which has no H to form intermolecular H bond, whereas the fatty acids have carboxyl group that can.
This paper is quite challenging, the level of difficulty is almost on par with some of the Prelim Schools exam papers.
I would say Ultimaonline gauge of difficulty would not be accurate. Every single year after taking the A level H2 Chem paper, he would say the paper is pretty standard. He is a private tutor, who is also an Ex-MOE teacher, with a Bachelor Degree in Science. Of course, to him , he would find the paper simple.
But to us, A level students, our maximum knowledge for Chemistry is merely just from the lecture notes and lessons from lecturers, which only sufficiently prepare us for the papers. But he has more than knowledge in chemistry as he pursued a degree in chemistry, of course, he has a unfair advantage over this.
So, in conclusion, the best estimate of how hard or how easy the paper is, is we students. The 2016 cohort, who are taking the paper to rate what is the difficulty of paper, by comparing with out peers in our JC. Ultimately, we are competing with the cohort in the different JC and not a tuition teacher.
The benchmark of the A grade should not be determined by Pte tuition teachers, (I'm fine with school teacher, they know how their students fare in A levels). As he himself is doing the paper as a pte candidate, then he would find it easy, like a stroll in a park, and he will set the same benchmark every year.
Of course, you could ask him questions about the paper , as it serves as a platform for learning, but never ask him about the A grade of the paper, he would not know? These are moderations made by the examiners, performance of entire JC cohort (30000 students), just merely few students of him is highly inaccurate...
For the reagent to remove double bond is it cold dilute KMnO4 with aq H2SO4?
Originally posted by ArJoe:So whats the reagents and conditions??
removing double bond is just Hydrogen gas with nickel catalyst at high temp and pressure! how come got KMnO4
Originally posted by Thefire521:removing double bond is just Hydrogen gas with nickel catalyst at high temp and pressure! how come got KMnO4
Originally posted by ArJoe:
Cause i thought vigorous oxidation can also remove double bond....
No lah, they just want to make margarine (saturated fat from unsaturated fat), so that means turning c=c to c-c
if you use KMnO4 and things like that its going to give you oxidative cleavage / form diol already what, which isnt what the question wants
but dont worry, since the exam is already over, it might be better to move on and work on the upcoming paper 3/harder math
Originally posted by Thefire521:No lah, they just want to make margarine (saturated fat from unsaturated fat), so that means turning c=c to c-c
if you use KMnO4 and things like that its going to give you oxidative cleavage / form diol already what, which isnt what the question wants
but dont worry, since the exam is already over, it might be better to move on and work on the upcoming paper 3/harder math
Originally posted by Thefire521:No lah, they just want to make margarine (saturated fat from unsaturated fat), so that means turning c=c to c-c
if you use KMnO4 and things like that its going to give you oxidative cleavage / form diol already what, which isnt what the question wants
but dont worry, since the exam is already over, it might be better to move on and work on the upcoming paper 3/harder math
then how did you draw the trans isomer when you only have an alkane after reaction?
Originally posted by Ccii:then how did you draw the trans isomer when you only have an alkane after reaction?
They gave you a structure of an alkene which is given after that part
Originally posted by Ccii:then how did you draw the trans isomer when you only have an alkane after reaction?
If you read the question carefully and properly, they did say that the trans isomer was "another" reaction - so not linked to the alkane.
Paper 3: Energetics, kinetics, Inorganic, Organic deductions, Ksp, Ka/Kb, titration graphs, chemical bonding and probably simpler and more straightforward questions
@ Thefire521
For converting C=C to C-C, can use H2 with platinum catalyst?
Originally posted by captainkidzs:I didn't mention about hydrogen bond. I just mention triester is spherical in shape and while the fatty acids aren't so less point of contact for van Der walls. is it possible?
I wrote the exact same response. Initially I thought hydrogen bonding would work but triester clearly outweighs the acids with the number of electrons in them so dispersion forces, by right, should be stronger. Hence I decided to argue from that point of view instead. Same boat.
Originally posted by Thomas00:@ Thefire521
For converting C=C to C-C, can use H2 with platinum catalyst?
Of course, many are possible, platinum, palladium, nickel..
i think in this paper there isnt much to discuss about as long as you studied your conventional arguments and applied them nicely you will probably score you full marks... Ultimately though there were more application questions, but they still bordered on the same old concepts (there wasnt anything out of the syllabus or new like coordination number in 2009) - so i guess wait for paper 3 since thats the one you can do better in if paper 2 wasnt a niche or forte!
yYeah I at first thought oh hydrogen bonds but after I see that anomaly and the shape then I zoom in to their shape