U1-June-2011-NS
Posted by: intechemistry on: September 24, 2010
Here we will discuss the Unit 1, June 2011 ‘New Syllabus’ past years papers (PYP’s):
Question paper:
Mark scheme:
13 Responses to "U1-June-2011-NS"
February 21, 2012 at 8:49 pm
18 b.CuSO4.5H2O would need heating (so temperature change cannot
be measured)
sir can you explain a bit on what it is all aout? the ans previously was + 77Kjmol-1 needed to convert the solid mentioned into CuSO4 (aq) form.
February 21, 2012 at 8:52 pm
Dehydration reaction cannot be controlled
OR
temperature change (of dehydrationreaction) cannot be measured
OR
CuSO4.5H2O would need heating (so temperature change cannot be
measured)
OR
impossible to add exact amount ofwater (to obtain value by reverse
process)
OR
cannot mix solid with water toobtain perfect crystals
the ans given, wld be g8 if u can put it in Lay-man-terms -simplest way to understand thanks
February 21, 2012 at 9:01 pm
1.Density of solution is taken as the same as water
2.approximation in (specific) heat capacity of solution
• neglecting (specific) heat capacity of calorimeter/apparatus (allow
energy absorbed by the apparatus)
Can you elobrate on the keypoints mentioned and what it means . one of the ans point is heat transfre from the surroundin , is it accepted if we write heat transter to the surroundin? Q 18 D (ii)
February 21, 2012 at 10:27 pm
”Photochemical smog is formed (0) NOx is produced (by reaction of
nitrogen & oxygen) (1) and reacts with (volatile) organic compounds in sunlight” ans sche Q19 B(IV)
Cn u xplin bit on wat it is meant for??
February 22, 2012 at 7:28 am
Dear Curious. Some Good Q’s there. But if I may,: please provide the number of the question as I really need to know context of your answer and the mark scheme. It’s also very draining on my time to have to try and hunt around the paper to find out which question you are talking about.
Secondly, this ‘discussion area’ is mainly to try and explain or justify things which may not make sense, either on the paper or the mark scheme. It’s not really to check peoples wording, so please, do try and minimize this type of enquiry here as the blog is rather and inefficient medium to address such enquiries. Seeing your lecturer is a much better way to address these type of enquiries.
If (I believe) your answer would score the mark on the mark scheme, I will write *YES*
February 22, 2012 at 7:29 am
1 | Curious, February 21, 2012 at 8:42 pm
Q 16 b) *YES*
Q 16 c) *YES*
February 22, 2012 at 7:29 am
2 | Curious, February 21, 2012 at 8:49 pm & 3 | Curious, February 21, 2012 at 8:52 pm
Q 18 b) Traditional ways of driving off the .5H2O from CuSO4.5H2O involve strongly heating it over a period of time, e.g. using a Bunsen burner on a crucible containing the salt. A LOT of heat is wasted, some also being absorbed by the crucible. It is impossible to measure the heat needed to specifically remove the H2O from CuSO4.5H20 only. It is experimentally impossible to add just enough hat (without heat loss) to drive off the H2O. Hence a Hess cycle is the only way to determine the energy needed is by a Hess cycle. It is VERY COMMON to use Hess cycles to determine heat changes that are impossible to measure experimentally.
February 22, 2012 at 7:32 am
4 | Curious, February 21, 2012 at 9:01 pm
I think you mean Q 18 c) ii)
The question says “(ii) The value for the enthalpy change from (c)(i) obtained by experiments in a school laboratory is likely to be significantly different from a data book value.
List three possible reasons for this which do not relate to the quality of the
apparatus or chemicals used or possible mistakes in carrying out the procedure.”
to which the answer was
“Any three from:
• heat transfer (from
surroundings) (allow loss or
gain)
• approximation in (specific) heat
capacity of solution
• neglecting (specific) heat
capacity of
calorimeter/apparatus (allow
energy absorbed by the
apparatus)
• reaction / dissolving may be
incomplete/slow
• temperature change is very
small (and difficult to measure)
• Density of solution is taken as
the same as water
• conditions not standard (allow)”
and rejected was
Errors in
calculation
including adding
mass of solid to
mass of water
loss of reagents
/ water
incomplete
combustion
Just ‘difficult to
measure’
If this question is (I think??) looking for errors present in determining the value in the data book and those used in the lab, which cause the two values to disagree. If there is a LOT of sources for error and/or the errors have a high error margin then that will cause a large deviation in the magnitude of the two values. Only a few sources of error each with very narrow margin of error within the particular source of error (e.g. source of error: measuring the temperate, margin of error being small as temperature change is very big) then there is likely to be very low divergence between the two values. So The question is essentially asking for sources of errors and by saying the values are “significantly different” then we can assume that the error margin within each source is big (e.g. if a volume was used then the volume must have been rather small, causing a high % error in the volume) As directed by the question, We must avoid answers like the school used a measuring cylinder but the data book value cam from using a pipette.
Does that clarify what’ going on here?
Whn you ask about “one of the ans point is heat transfre from the surroundin , is it accepted if we write heat transter to the surroundin?” – I would say no. Heat flows from to areas of higher temperature to that of lower temperature, so you answer suggests the system has the greater temperature which is the opposite of the mark scheme.
February 22, 2012 at 7:33 am
5 | Curious, February 21, 2012 at 10:27 pm
R2: Q *19 (b)(iv)
The context of the Q is about the COMPLETE combustion of alkanes in air
In air there is N2(g). The heat of the reaction can all ow the N2 and O2 in air to also react. Forming oxides of nitrogen. The “Photochemical smog is formed (0)
NOx is produced (by reaction of
nitrogen & oxygen) (1) and
reacts with (volatile) organic
compounds in sunlight (1)” answer addresses the NOx here. The answer “Photochemical smog is formed (0)” means that answer scores zero marks. The other answers and marks are I think clear.
February 22, 2012 at 5:36 pm
Dear Sir. Trials in few days and I knw you will understnd. That xplains the mess.
”It’s also very draining on my time to have to try and hunt around the paper to find out which question you are talking about.” Loooool. Touched by ur dedication Sir & its hard to find an individual in resemblance to ur dedication. thats a very fast reply Thank ya Sir 
))
”Seeing your lecturer is a much better way to address these type of enquiries.” Thanks for d idea Sir, Yes it surely IS, which is seeing You.
9)” Does that clarify whats going on here? ” no nt reli Sir my Q was for to xplain it to me wat the key point addresses preferable the last two wich is as stated below (bcoz i managd to fully understand the rest =))
- Density of solution is taken as
the same as water &
-conditions not standard (allow)”
February 22, 2012 at 7:38 pm
11 | Curious, February 22, 2012 at 5:36 pm
Sorry I missed the focus of your enquiry.
The mass of water, ‘m’, as used in m x c x delta(T), is arrived at by considering the total volume of liquid used. If say 50cm3 was used, it will be assumed there is 50g of water. BUT that volume actually contains other species, like Cu ions and (SO4)2- ions and so on, it’s not pure water and the density won’t be exactly 1g/cm3, therefore the volume of the liquid used isn’t going to give the equivalent mass in grams. There will be a small error due to that.
The conditions used in a school are not likely to be able to fix the temperature of the experiment at 25oC, which is what the data book value will be based on (the data book is reporting delta(H)standard values.
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February 21, 2012 at 8:42 pm
Hi Sir,Would this be accurate to the ans provided.-score mark
1. ANS SCHM ;Shielding (of nucleus)(about) the same (1)
mine ; shielding effect across the period remains same
2) ANS SCHEM
Electrons (in the p sub-shell) are paired (for the first time) (in S) /
two electrons occupy the same (p) orbital / full orbital / electrons-inboxes
diagram (1)
MINE ;The electrons in the p-orbital of S is paired thus the repulsionof the pair of electrons will cause a lower amount of enery to remove the electron in I.E.