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
Lol later half of the paper = electrochem D:
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?
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)
sry, one last qns: May I ask usually, how many marks they'll increase for grade A, if you said it's slight?
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.
Good luck for A levels !
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.
Originally posted by UltimaOnline: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.
LOL at cambridge. thank god i eliminated the first option
thanks alot .
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.
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.
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?
Oh..my ans was C..cuz they asked for the rxn between Cu 2+ and I minus...I thought the Cu 2+ will be reduced to reddish ppt Cu first...so the E cell potential should be that of Cu2+ --> Cu for the reduction half-cell
sorry..then, may I ask what the brown ppt formed is?
http://en.wikipedia.org/wiki/CuI
In the laboratory, copper(I) iodide is prepared by simply mixing an aqueous solutions of sodium or potassium iodide and a soluble copper(II) salt such copper sulfate.
The CuI2 immediately decomposes to iodine and insoluble copper(I) iodide, releasing I2.[5]
but what exactly is the brown precipitate formed?.It must be copper, right?