OCR Salters Chemistry of Materials 2849
Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.
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Re: OCR Salters Chemistry of Materials 2849Ca should be 2+...(Original post by kitty123)
For the CaCO3 question I put Butanoic acid + CaCO3 - - - -> CH3(CH2)2COO-Ca+ + HCO3??? I have absolutely no idea if thats right but I remember a question about it but it involved Na not Ca. Oh no I think I might have put Na instead of Ca! My life can't get any worse right now
but iv no idea how to balance the equation...
i put
2C3H7COOH + CaCO3 ---> 2C3H7COO- Ca2+ + CO2 + H2O
how do u balance the charge? -
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Re: OCR Salters Chemistry of Materials 2849Lets stop thinkin about it!(Original post by kitty123)
Haven't got a clue, anyone else have any ideas? It was only 1 mark wasn't it? I think I have about 50% on this paper Dammit!
Get more marks in Chem by design(next thurs)... to compensate for 2days loss!!
the full marks of chem by design is 120... which is 20% of the whole alevel!!!
Hopefully we both get the grades we need! -
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Re: OCR Salters Chemistry of Materials 2849I put H-bonding... might have been wrong though, not really sure.(Original post by j_c_rox)
PET has perm.dipole, perm dipole right?
That zwitterion question: there were 2 amine groups and one carboxyllic acid. The H+ from the COO- had gone to the top NH3+, leaving one NH2 with a free lone pair to accept a proton.
I gave the wrong explanation in the exam, but I'm pretty sure this is the right one.
Also: I put pink to colourless, or maybe the other way round, had no idea. -
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Re: OCR Salters Chemistry of Materials 2849I was pretty sure that PET showed hydrogen bonding, which obv is stronger than the perm dipoles. I was so lucky with the rust, just before the exam i was doing a past paper nd rust came up so i looked at the mark scheme and wrote all the answers down- the exact same Q's came up! I couldn't do the 5 mark calculation tho!
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Re: OCR Salters Chemistry of Materials 2849lol, i memorised that answer too from a past paper(Original post by mentally-guitarded)
For the last one i put,
Iron being a transition metal produces ions with variable oxidation states. The Fe ions interconvert in the redox reactions and remain unchanged. The Fe ion also lowers the activation enthalpy for the reaction, allowing an alternative, lower energy reaction pathway for the reaction.
I remember doing a very similar question in one of the past papers, might have been the spec paper. These were the three points on the mark scheme. -
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Re: OCR Salters Chemistry of Materials 2849kitty123 65/90 made a B
got the electrode potential question wrong. i wish i had looked at the equation more carefully and realised IRON was getting oxidised.. oh well.. like someone said above i hope we are given a mark or two for sayng zinc has a more -tive electrode potential than Fe and its a stronger reducing agent and blah blah.
probably lost a mark coz i couldnt balance the ester's reaction with CaCO3.
aint sure about the ppt question either. where they were askng what colour ppt is formed when excess OH- is added or sumthng ?? and another one the formula of some ppt... ?? cant remember exactly. Am i making any sense or have i completely lost it
what did everyone rite for a polymer coating steel as compared to zinc?
and there was a question about clinical trials. thats all i can remember
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Re: OCR Salters Chemistry of Materials 2849I wrote something along the lines of the polymer coating prevents oxygen and water coming into contact with the iron by making a waterproof seal kind of thing. Then with zinc, the zinc has a more negative electrode potential so will oxidise instead of the iron... or something like that.(Original post by 50PH///)
what did everyone rite for a polymer coating steel as compared to zinc? -
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Re: OCR Salters Chemistry of Materials 2849I wrote the crappest answer- I said the polymer after a while will disappear.(Original post by 50PH///)
what did everyone rite for a polymer coating steel as compared to zinc?
I write the damned foolish things under pressure. -
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Re: OCR Salters Chemistry of Materials 2849Zink: sacrificial protection, greater tendency to oxidise and form ions.
Polymer: barrier protection, prevents oxygen and water from getting to the iron and making it form Fe2+ ions.
With the rust question, did you have to add in 4 electrons to ballance the charges on the equation involving oxygen and water?
No idea about the changes you'll see, I said form a blue ppt, because it rang a bell from past papers. -
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Re: OCR Salters Chemistry of Materials 2849(Original post by james s)
Zink: sacrificial protection, greater tendency to oxidise and form ions.
Polymer: barrier protection, prevents oxygen and water from getting to the iron and making it form Fe2+ ions.
With the rust question, did you have to add in 4 electrons to ballance the charges on the equation involving oxygen and water?
No idea about the changes you'll see, I said form a blue ppt, because it rang a bell from past papers.
Thanks.
for the rust, i think it is 2H20 + O2 + 4e --> 4OH-
or H20 + 1/2 O2 + 2e --> 2OH-
for the chnge of colour i cant rely remember what iv written .. wat was the oxidation state of iron does any1 remember? i think +3 gives a brown colour (eg Fe(OH)3 is brown ) and +2 gives green (Fe(OH)2 is green). correct me if am wrong -
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Re: OCR Salters Chemistry of Materials 2849i just put pink too.
i can't really remember any more questions.. i was lucky with most of them cos i'd seen past papers that morning with pretty much the same questions..
The one i wasnt sure about was one of the last ones where it just randomly asked you to draw the ion.. i didnt even realise it was a question first time round because there was just a gap, no indicatio that an answer has to be written there!
I also wasn't sure about the clinical trials i think i put something stupid like 'make sure its not toxic' which surly they would check before testing on humans. nevermind eh.
Dreading 2854 though.. -
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Re: OCR Salters Chemistry of Materials 2849Oh yeah, I said ensure by-products aren't toxic and check the effectiveness against a placebo.(Original post by sarzbabe)
I also wasn't sure about the clinical trials i think i put something stupid like 'make sure its not toxic' which surly they would check before testing on humans. nevermind eh.
