H2 Chemistry 2013 'A' Levels P2 & P3 & P1

last SG · 2013-11-25T17:34:48+00:00

what's the transition planning about? any stunner questions?

UltimaOnline SG

I posted :

Considering the difficulty of all 3 papers, as well as how all the Singapore JCs have primed their students for a super killer paper, it's most likely around 75%. But 73% for A grade is still very possible, and I don't want to overly dishearten the many students who scored between above 70%, but less than 75%. It's actually still possible that Cambridge might still allow an A grade for 71% or 72% this year. Though my final guess is between 73-75%.

PizzaTeddy posted :

Well our college heard that HCI told their students 80-85%, which definitely scared us out of our wits. Hopefully its just a rumour haha

I posted :

That's just BS. Don't trust those who exaggerate and sensationalize.

As long as you have approximately 75%, your A is secure.
As long as you have above 70%, you still have a good chance at getting A.

Enjoy your Dec holidays, results should be released on 3rd March 2014.

Bryannn posted :

WOAH 80% is insane! I don't know how it can go up that high and how you guys calculate the projected A grade but from what I know(from friends and in this forum), only paper 2 is tough and others are very easy but with lots of carelnessso should it be safe to assume to get an A,candidates should score above 75% for ALL papers except paper 2? If so,it should be something like (0.75 X 65 + 0.7 X 35) = 73.5%.
That's like wayyy below 80%,even 75% would be alittle too farfetched. Haha.

I posted :

Interesting that your estimate of 73.5% is curiously close to mine, between 73% and 75%.

75% isn't as far fetched as some might like to think (or desperately hope for), but 85% (supposedly HCI's estimate) is just plain BS.

And I already said in an earlier post, 80% is the upper possible limit, but even then, very unlikely for H2 Chemistry to ever hit this threshold on the bell-curve.

And as I said earlier, there's still a chance that Cambridge might still allow an A grade at 71% or 72%, so those of you at the boderline threshold, take heart, you still stand a chance to get your A grade.

Apply realistically for a variety of Uni courses within your reach; take the time now these couple of months, to find out more about all the Uni courses. And as a last resort, if your overall UAS falls short of all your desired courses, retaking your A levels isn't as bad as you might think.

CaiHongRainx SG

Do you think HCI said is 80% because of spa? Cause I thought normally almost every student would get the full 15% for spa, thus making 80% realistic and possible?

UltimaOnline SG

Do you think HCI said is 80% because of spa? Cause I thought normally almost every student would get the full 15% for spa, thus making 80% realistic and possible?

SPA is problematic, and to some extent, skewed differently in different JCs, abit akin to PW, but not quite as biased and unfair.

Still, majority of students score closer to 10% rather than the full 15%, and there are always failures in every JC, even for SPA.

80% for A grade for H2 Chemistry is not impossible, but not realistic and very unlikely, especially after considering the difficulty level of the 2013 H2 Chem papers, each of which did contain a very fair range of easy, standard, and difficult questions.

I still stick to my estimate of 73-75% for A grade this year.

Cycloneeee SG

Err really seriously people, why are you guys debating about the answers and all!? Whats done is already done! Just move on and study for your next paper and wait for the results to be out next year! Lol is there any use predicting how many % you need to get A n stuff!!!? Its all up to cambridge! Comparing answers will do you no good except drive you into depression.

alycx SG

Hi. Could anyone kindly tell me why the answer to 8 is not A? The temperature falls from 25 to 0 degrees, isn't it less disorder, hence negative?

Also, why is it radius of atom is the answer to 13 and not electrical conductivity? And lastly question 19, I cannot locate the fifth chiral centre.

Thank you!

UltimaOnline SG

Hi. Could anyone kindly tell me why the answer to 8 is not A? The temperature falls from 25 to 0 degrees, isn't it less disorder, hence negative?

Also, why is it radius of atom is the answer to 13 and not electrical conductivity? And lastly question 19, I cannot locate the fifth chiral centre.

Thank you!

Entropy change is linked, but not necessary directly the same, as temperature change. For instance, a reaction could be endothermic, but result in a greater number of species on the RHS (relative to LHS), and so more species = more entropy.

Since the enthalpy change is endothermic (ie. thermodyanically unfavourable), as evidenced by the fall in temperature, and yet the Gibbs free energy change is negative (ie. thermodyanically favourable), it means that the entropy change must have been sufficiently positive (thermodyanically favourable) and large in magnitude, to have outweighed the thermodyanically unfavourable endothermic enthalpy change, such that the overall Gibbs free energy change was negative and thermodyanically favourable.

Electrical conductivity increases from Grp II to Grp III (since more delocalized valence electrons to participate in electrical conductivity) before dropping. Not consistently decreasing.

5th chiral carbon? It's there all right. Treat it as a fun puzzle and keep looking for Wally.

UltimaOnline SG

Posted by Prototype445

The anion in this question, refers to the peroxide anion :

Ilovechem SG

Hi isn't qn 4 B? The I.e given resembles Ti in data booklet and also TM have similar IE. Thus the element given is a TM!

UltimaOnline SG

Hi isn't qn 4 B? The I.e given resembles Ti in data booklet and also TM have similar IE. Thus the element given is a TM!

Transition metals have variable oxidation states, and thus could form multiple chlorides. The question specifies that this unknown element only forms one possible chloride.

Blanklorh SG

erm for qn 36, i worked out the elec config of In to be 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p1

to my understanding, partially filled d orbital shld give colour no? then ionic salt of In(III) ought to be able to have a d-d transition isnt it? hence the colour?

UltimaOnline SG

erm for qn 36, i worked out the elec config of In to be 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p1

to my understanding, partially filled d orbital shld give colour no? then ionic salt of In(III) ought to be able to have a d-d transition isnt it? hence the colour?

Good thoughtful effort, you did indeed successfully work out the electron configuration.

But unfortunately, you're slightly off target when it comes to ionizing, as electrons are always removed from outer quantum shells first :

In = [Ar] 4d10 5s2 5p1

In+ = [Ar] 4d10 5s2 5p0

In2+ = [Ar] 4d10 5s1 5p0

In3+ = [Ar] 4d10 5s0 5p0

Hence In3+ in it's ionic salts have a fully filled d subshell, hence no d-d* electron transitions, hence it's ionic salts are not coloured.

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Posted by Prototype445

It's not valid to assume all Group III elements have the same chemical properties. Not a valid shortcut.

Rather, the correct valid shortcut to this question, is to recognize that Indium is a p block element, not a d block element, and so cannot have partially filled d orbitals in its compounds, which therefore cannot be coloured.

Blanklorh SG

oh no TT given this paper im wondering if my approx 31/40 is even a good enough grade. almost all are due to carelessness :/

UltimaOnline SG

oh no TT given this paper im wondering if my approx 31/40 is even a good enough grade. almost all are due to carelessness :/

31/40 = 77.5%.

If you did similar or better for your other papers (including SPA), then your A grade is very secure.

This year's A grade threshold on the bell-curve should be between 73-75%.

Dunnolah95 SG

Thanks for the answers! May I ask, for question 34, why is the answer B instead of D? Isn't the anion O2-, so the number of electrons should be 10?

UltimaOnline SG

Thanks for the answers! May I ask, for question 34, why is the answer B instead of D? Isn't the anion O2-, so the number of electrons should be 10?

The anion in this question, refers to the peroxide anion :

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