Final Advice for H2 Chem Paper 2 tomorrow

last SG · 2009-11-25T14:45:10+00:00

no. if i am not wong its iodine.

UltimaOnline SG

For the next half an hour, revise your notes (CS Toh’s ‘A’ Level Study Guide or your own JC lecture/tutorial notes) on
(i) Inorganic Chemistry (Periodicity, Grp II, Grp VII, Transition Metals).
(ii) ElectroChemistry.

If you’re stuck at any question, skip it and return to it later to save precious time.

Sleep for approximately 7 hours. (ie. sleep at about 11pm, wake at 6am).

Enjoy a delicious breakfast before you sit for your paper (sufficient glucose for your brain).

tut4nkh4m3n SG

i'm reading this only now. but anyw, generally focussed on the same topics except GVII. sadly, electrochem hardly came out for papers 2 and 3. hmmm. no dot and cross diagrams either.

on the whole, the paper was different. even the organic question was not that straightforward esp towards the end.

yuppers

UltimaOnline SG

Yes, that’s what my students said. Odd though, that this year Cambridge put electrochem only in P1.

Wheref SG

Lol later half of the paper = electrochem D:

Lin.thitlwin SG

May I ask if for H2 Chem, they have ever moderated very highly for grade A before?.. e.g. 73 or above...Cuz this yr's chem paper 1 was generally hard for everyone...do you think they'll moderate?

Lin.thitlwin SG

Also, for chem P3, they asked 3 ways in which the properties of ideal gas differ from a real gas...can it be the 3-4 assumptions of ideal gas? (e.g. negligible forces of attractions between gas molecules)

UltimaOnline SG

Regarding the ideal gas question, yes that’s what they’re asking for.

As for moderation, almost every year there’s always moderation, although it’s usually slight. Either moderating updwards or downwards. They’ll never reveal the actual score used for each grade each year though.

It’s useless to worry about your grade now. Let Cambridge and SEAB settle that. Focus the next couple months on finding out more about your University study and professional career options that is suitable for you. Make well-informed choices. That’s far more important (than worrying).

Lin.thitlwin SG

sry, one last qns: May I ask usually, how many marks they'll increase for grade A, if you said it's slight?

UltimaOnline SG

Can be anything from 0.1 to 10. They will never reveal.

Lin.thitlwin SG

I have 2 chem questions to ask...

(1). Use of data booklet is relevant to this question

Hydroxyapatite, a basic calcium phosphate, Ca(OH)2.3Ca3(PO4)2 is the mineral found in bone. Older people may lose calcium ions from the hydroxyapatite, weakening the bone structure. For such cases, strontium ions are administered to stregnthen the bone. The Strontium ions replace the lost calcium ions in the hydroxyapatite. Which statements are correct?

1. Strontium ions are nearly the same size as calcium ions and so may easily replace them in hydroxyapatite.

2. Strontium hydroxide is more soluble than calcium hydroxide an d so will precipitate bettwe in the bone structure.

3. There is ionic, covalent and metallic bonding in hydroxyapatite which gives its strength.

Options A (1,2,3), B (1,2), C(2,3), D(1 only)

(2). The eqaution represents a reaction.

Alkene + Bromine (in a polar solvent) ----> dibromoalkane

Which statement about this reaction is correct?

A. Bromine acts as an electrophile

B. It is a free-radical substitution

C. It is a nucleophilic addition reaction

D. It only takes place in the dark

I'm Just in need of the answers, thanks.

ƒlame SG

Good luck for A levels !

UltimaOnline SG

Strontium vs Calcium. Sr has one more electron shell than Ca, so do you think they are “nearly the same size”? The reason why Sr easily replaces Ca, is because they’re both in Group II and have similar chemical properties.

In the first step of the mechanism, the pi bond of the alkene is the nucleophile which attacks the partial positively charged Br electrophile. In the second step, the bromide ion Br- nucleophile attacks the cyclic bromonium/carbocation electrophile.

The name given to the reaction is dependent on the initial first step, not the subsequent or second step.

Lin.thitlwin SG

However, for the strontium question, if option A is wrong, then I don't think there is an answer already. Cuz I thought options B and C are wong too. E.g. For B, if Sr(OH)2 is more soluble how will it precipitate better? (It should be dissolving better, isn't it?). For toption C, I can't identify any metallic bonding (between the metal cations and the delocalised electrons).

Thank you for your response.

UltimaOnline SG

You’re right that this question and its options leave something to be desired. (But it’s certainly not the 1st time Cambridge gives terribly phrased questions/options.)

Some MCQ questions you have to solve by elimination, since the ‘A’ level syllabus doesn’t specifically study the bonding of hydroxyapatite. In other words, Cambridge can argue the question is ‘fair’ even if it’s partly beyond the syllabus because the student is expected to be able to cope by elimination.

As for solubility, what the (poorly phrased) option means is that since Sr(OH)2 is more soluble (than Ca(OH)2), it is able to be transported along the blood in the form of aqueous Sr2+ ions easier (compared to Ca2+) into the bone, whereupon it will then take the form of hard, insoluble hydroxyapatite.

tut4nkh4m3n SG

You’re right that this question and its options leave something to be desired. (But it’s certainly not the 1st time Cambridge gives terribly phrased questions/options.)

LOL at cambridge. thank god i eliminated the first option

Lin.thitlwin SG

thanks alot .

Lin.thitlwin SG

Sry, but I've got 2 more qns

(1). Use of data booklet is relevant to this question

When aqueous solutions of CuSO4 and KI are mixed, a brown ppt is formed. On the addition of aqueous sodium thiosulphate to this mixture, the brown colour disappears and a white ppt remains. What is the standard cell potential of the reaction of KI with CuSO4?

A. +0.39V B.+0.20V C. -0.20V D. -0.39V

Is the option C correct? Cuz after calculation, I got a negative value of 0.20V but why does the rxn still proceed?

(2). Aluminium hydroxide has a decomposition temperature of 573K. It is mixed with titanium dioxide to produce a paint which delays the spread of flames in the event of a fire. Which statement explains why Aluminium hydroxide is used in this way?

A. It is acidic enough absorb any ammonia in a fire.

B. Water vapour is produced on decomposition

C. It reacts with acid produced on combustion

D. A large amount of energy is absorbed when aluminium hydroxide vapourises.

Is the option B correct? Cuz I thought the water vapour produced will help reduce the spread of flame.

tut4nkh4m3n SG

why are you asking so many questions from the paper when it's already over. give yourself some peace. IF I RMBR CORRECTLY, first question's ans should be C. second one i'm not entirely sure but i put B.

UltimaOnline SG

Q1. The reaction proceeds because the reaction doesn’t take place under standard conditions, and the question is asking for the cell potential under standard conditions.

Q2. Burning petrol and charcoal also produces water vapor. Will firemen spray petrol or throw in stick of charcoal to put out fire? Think about why LIQUID water is able to put out fire. What can you say about the strength of the hydrogen bonds between water molecules? What does this have to do with putting out the fire? It is the same principle why aluminium hydroxide or magnesium is used as a fire retardant.
http://en.wikipedia.org/wiki/Magnesium_hydroxide

And give tut4nkh4m3n’s suggestion to move on, enjoy yourself for a couple weeks, and then prepare for University choices, a shot.

arxoz SG

isnt the answer for the first qn posted by Lin.thitlwin is D as Cu2+ is reduced to Cu+ as CuI(white ppt) is formed?