Chemistry paper 42 may/june 11

[diwash]

hello every one..
I think we can discuss the paper now..

what was the answer of that electrolysis Q...
i think AgF, FeSo4, and MgBr2 were the compounds...

 

[beacon_of_light]

I wrote oxygen produced at all anodes while Ag, and hydrogen at cathodes ...wat did you write?

 

[bionology]

Oxygen at all anodes but bromine at one,
And Ag + Hydrogen on others

 

[beacon_of_light]

Why bromine at one? can u explain ? I checked out the electrolysis of MgBr2(aq) and the products are oxygen and water!

 

[bionology]

might be you are correct, I just thought of the electrolysis of chlorine, it was always chlorine at the other electrode. Anyways,
what was that DNA fingerprinting one answer? Used for another purpose?

 

[beacon_of_light]

I wrote genetic relatedness to parents ... wat abt u ?

 

[bionology]

same here,
and how did people at your side find the paper?
I just messed up at phenyl question, wrote the opposite of electron withdrawing group, halanke i knew it, but just mixed up
the polymer was kind of tricky but rest was fine.
I guess threshold will be 65-68

 

[beacon_of_light]

Paper wasn't that difficult... However many people here didn't do well. Which phenyl question? Oh u mean water ethanol and phenol ?

 

[angelgurl]

i think the organic part of the paper was tough specially the one on polymers!!! when he said stereoisomerism i crossed all my answer out which was condensation monomer and then made it into an addition monomer using a double bond and then again made cis trans isomers
i wrote use of DNA fingerprinting for plant materials!! he asked about how goat skins are related.......... i thought paper is plant material so maybe we can use DNA fingerprinting to identify which plant it came from!!
and guys wht was the radioactive isotope??? and wht was abt tht polymerase chain reaction was the isotope supposed to be used in this reaction?
and wht was ur value of avogadro constant mine came 1.21x10^22 which is basically wrong and i was like so sad abt tht part!!!
btw no difficult chapter like transition metals or NMR came so the paper seemed to be easy though i dont think it was and if it was easy then he's going to do very strict marking!! and many ppl have made mistakes so i hope gt falls really low!!

 

[beacon_of_light]

That was condensation polymer I think because the functional group in the polymer was "ester" ... but when we dehydrated the polymer with Al2O3, we got a double bond i think ...
And what about the stereoisomers ... wat was the monomer...i wrote HO-CH(C2H5)-CO2H (so this compound showing optical isomerism as it was asked) and when dehydrated we get two cis-trans isomers... CH(CH3) --- CH(CO2H) Did u do like that?

 

[diwash]

I wrote oxygen produced at all anodes while Ag, and hydrogen at cathodes ...wat did you write?

ya dude..i also got the same answer..i think its the right one...

 

[bionology]

transition elements came ! the complexes one was a part of transition
the isotope was radioactive phosphorous(thanks to A2 biology)
Polymerase one is used to increase the DNA length
avogadro was 5.9X10^23. You'll get 2 marks it u used F=le at the end, or you calculated F etc, every step has a mark, however you may not score full marks
yes that was condensation reaction with 2 OH attached in the monomer

Generally people did mistakes, but comparatively the paper was easy, especially no tricky organic reactions ! However, all types of candidates appear in the May/June, so every kind of response is seen, The GT will never touch 70 but will not fall below 60, hope it ends up good for us

 

[beacon_of_light]

yeah yeah copper ammoinum sulphate had deep blue colour and when diluted cos of ligand exchange colour became blue...
btw anybody plz comfirm the steps for electrophoresis...
--extract DNA
--polymerase chain reaction
--place on agarose(i don't remember whether that was a step)
--carry out electrophoresis
--radioactive phosphorus probes
--forgot the last one...

 

[bionology]

yes I did the same
and the ph was i guess 2.3 or something?
what was the reaction below this Ph question?
the conditions were to increase the temp as the reaction was exothermic and wuld lead to backward reaction (decomposition)

 

[beacon_of_light]

I made a big blunder!!! I thought 1 tonnee = 10,000kg and got 62.5kg... wat abt others?

 

[bionology]

btw we had to add that the solution was blue/green due to presence of both the 'aqua' and 'other' ligand (i dont remeber it) . However when the excess of water is used, ligand exchange takes place and aqua one's replace the existing ligand resulting in similar solution colour, correct me if iam wrong

 

[bionology]

I made a big blunder!!! I thought 1 tonnee = 10,000kg and got 62.5kg... wat abt others?

do not worry, human error, lol, he will deduct 1 mark only, and give u the other 1 mark

 

[beacon_of_light]

NH3 was the only ligand in {CU(NH3)4} SO4 ...so wouldn't that be deep blue ?? :s
yeah we had to mention ligand substitution ...

 

[beacon_of_light]

yes I did the same
and the ph was i guess 2.3 or something?
what was the reaction below this Ph question?
the conditions were to increase the temp as the reaction was exothermic and wuld lead to backward reaction (decomposition)

yeah ph was 2.28 or 3... below the ph part, we had to draw dot and cross structures of NH3, NH4+F- and HF... and we had to tell the 3 types of bonding in NH4+F- ... i wrote ionic bonding b/w oppositely charged ions, covalent bonding b/w N and H ... and dative bonding b/w N and F ... i hope that's right?

 

[beacon_of_light]

yes high temperature and low pressure ..didn't they ask for "TWO" conditions...