2016 A Level H2 Chemistry Paper 2, 3, 1 discussions

last SG · 2016-11-08T20:10:45+00:00

I would think they should accept only NO2+S02=SO3+NO then regeneration bla bla blaso its like a homogeneous catalyst and Oxidising agent i would think elect...

qsx SG

The NxHy partial pressure is 1.4E10^-10, is it correct?

And the heterogeneous catalyst I need to mention about desorbed ,adsorbed, adsorption and surface concentration and weaken the bond. Is there some more need to be added?

TheSpaceManatee SG

For the Cu and ammonia question,

I believe you have to use the Cu + NH3 = [Cu (NH3)4]2+ Eqn and the alkaline reduction of O2 to form ur ionic eqn

Specifically, the Cu exists as a solid metal (s), and not an ion, so you should not have it become the cuh2o62+

Pardon me maybe a stupid question but the alkaline oxygen reduction equation I used was O2 + 2H2O + 4e- ---> 4OH- correct?

@qsx I also said lower activation energy of the reaction but not sure if required.

Kiddo1998 SG

Will you be spotting the topics for H2 chemistry for paper 3? Thanks

Thefire521 SG

Yes i think the partial pressure seems right but in 3sf.

Since the q was only 2 marks for explanation and only asking how it increases the rate of reaction (and not the whole mechanism), the answer should focus mostly on increasing concentration, higher number of effective collision, correct orientation and also straining critical bonds so lower activation energy.

Yeah thats the right O2 eqn to use

qsx SG

I think the Cu and NH3 should directly find from the data booklet

2Cu + O2 + 2h20 + 8NH3 --> 2[Cu(NH3)4]2+ + 4OH-

theophilus SG

thanks ultima your chemistry wisdom has benefited society haha

Last question, for the Cu taking long time to oxidize, only because CuO is formed ah ? no other possible explaination ?

ArJoe SG

Hi, for the heterogeneous question, i wrote partially filled 3d orbitals, reactant adsorbed onto catalyst surface, form temporary bonds, weaken bonds between reactant molecule, lowee activation energy, increase reactant concentration by bringing them closer. Frequency of effective collision rises.

For the cu and k qn, i quoted ie values, then said cu have higher nuclear charge and shielding effect, the additional 3d electrons provide shielding effect which largely nullifies the increase in nuclear charge, cu have higher effective nc, valence electrons more strongly attracted to nucleus, less easily oxidised

For cu reacting with acid, is it cu becoming cu+ or cu2+?
and can no2 be causing global warming? I thought respiratory isnt acceptable because they said environment?

Thefire521 SG

For cu reacting with acid, is it cu becoming cu+ or cu2+?
and can no2 be causing global warming? I thought respiratory isnt acceptable because they said environment?

Heterogenous-standard explanation

Cu and K- quoting probably gives free marks but then your explanation later should follow on what you quote. For example, if you quote I.E then your explanation should be on why lower I.E higher reactivity for K compared to Cu, but if you chose the otherwise option and decided not to quote from data booklet and instead talk about nuclear charge etc, then it should also be fine. But you cannot quote one thing and explain about another thing.

I would think Cu+ E value is 0.52 whereas the Cu2+ is 0.3something so Cu can be oxidised to either, its probably the safest to write both in and say E cell <0

Its not respiratory that is the environmental effect, its the photochemical smog. And they should accept global warming+acid rain as well as they are all valid

TheSpaceManatee SG

For cu reacting with acid, is it cu becoming cu+ or cu2+?
and can no2 be causing global warming? I thought respiratory isnt acceptable because they said environment?

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?

ArJoe SG

Hi i think my explanation do follows, since if cu have higher effective nuclear charge, then more energy is required to remove valence electron from cu, cu undergoes oxidation less readily and hence less reactive.. isit

ArJoe SG

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?

Yup very scared of the cu qn... and i dont even know whether i used the correct acid ewuation. When i quote the equation and value i didnt use reversible arrow..

Thefire521 SG

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...

captainkidzs SG

may I check what's the answer for qn 1 part 1? the one about MP

Thefire521 SG

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..

theophilus SG

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

Zhhh_ SG

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?

Jlptj SG

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.

ArJoe SG

Hey for the shortening of carbon chain, is it acidified kmno4 aq, heat?

captainkidzs SG

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?

Thefire521 SG

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.

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