Official A2 OCR Chemistry Practical Thread Watch

mysteryman
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#1
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Ok peeps only 5 days to go before we got this. So to prepare all of us for this can people put in this thread what we should revise to prepare us, as it could be anything not just a titration so we don't wanna be caught out. Thanks
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Aired
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We were given the A2 specification for the practical exam, and it says it could include...

> Volumetric analysis based on a set of titrations.

> An experiment that may involve the determination of some physical quanitity, i.e. determination of a rate constant or the order of a reaction, or the determination of an enthalpy change for a reaction.

> An observational problem in which the candidate will be asked to investigate, by specified experiments, an unknown substance or mixture.
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evil groove
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(Original post by Aired)
We were given the A2 specification for the practical exam, and it says it could include...

> Volumetric analysis based on a set of titrations.

> An experiment that may involve the determination of some physical quanitity, i.e. determination of a rate constant or the order of a reaction, or the determination of an enthalpy change for a reaction.

> An observational problem in which the candidate will be asked to investigate, by specified experiments, an unknown substance or mixture.
Hi Aired. You said that the specification says that the practical exam 'could include...' Does that mean that OCR cannot ask us anything other than the things in the above three points?
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sarah12345
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we need to know the following tests
- for a carbonate anion
- for chloride, bromide and iodide anions
-the test for unsaturation
-test for an aldehyde
-presence of an ester
-presence of a primary or secondary alcohol
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shyopstv
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Well the plan was a redox titration so there is a good chance that it would be one of those but I doubt that it is the potassium managanate and iron one that we did in the plan because that they have already done that once a couple of years ago

Another thread spoke about an indicator that turns from pale green to purple which I have never heard of (something to with vanadium maybe?) but if that is that case then there is almost definatly a titration in there somewhere

I would also guess that there will be some test tube tests like in previous years but I doubt they will be organic tests as this has no relevance to the plan we did. It would still be best to know about it though. One other thing it might be helpful to know is the colours of some of the transition metal ions like how iron(III) turns red if you add thiocyanate (i think) because they could easily link that in if it is a redox titration

Obviously it could also be something entirely different. It might also be wise to look up how to measure enthalpy change (and the E=mcT formula) and also rate equations.

*hopes that if there are test tube tests it is something easy like adding silver nitrate to test for halide ions


Oh and I was also told by the lab techician that it is a really hard practical to set up but then our lab technician is really weird so that might not be relevant
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Aired
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From what people have been saying, it could be something similar to this:

http://www.emailed.org.uk/exams/2816_03_Jan_03_TEST.pdf
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mysteryman
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Given the plan was finding % purity, in theory it could be find % purity of anything even could be organic involving reflux *hope not*. If its similar to the above that aired suggested then it shouldn't be too bad. Just learn all evaluation points they are always the same near enough.
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sarah12345
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whats the test for a carbonate????
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Solid_L
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Add acid perhaps to see if carbon dioxide is given off (lime water -> cloudy..)

God this practical is giving me a head ache, we haven't even finished the syllabus yet! Damn teacher!

I didn't think organic chemistry would be on...what are the tests for the organic things mentioned by Sarah above?
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sarah12345
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(Original post by Solid_L)
Add acid perhaps to see if carbon dioxide is given off (lime water -> cloudy..)

God this practical is giving me a head ache, we haven't even finished the syllabus yet! Damn teacher!

I didn't think organic chemistry would be on...what are the tests for the organic things mentioned by Sarah above?

i THINK
-unsaturation you use bromine water (orange--> decolourised)
-aldehyde- tollens reagent (silver mirror formed)
-ester has a fruity smell
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Solid_L
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Yes the bromine water is right... but I don't think that is the best test for an ester, maybe the splitting of the ester into alcohol and carboxylic acid...then a test for 1 of those, would be the best course of action.
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mysteryman
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No a test for an ester is just fruity smell, it says so on specification.
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mysteryman
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Its probably gonna be a redox titration our teacher has been doing a lot of titration calculations and half equations and oxiation states with us. As well as that loads of sulphuric acid has been missing from out lab. So maybe dissolve something to make a standard solution. Make iron tablets *just a guess although i seriously doubt it maybe an iron alloy*.
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igloo
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My chem. teacher reckons that it is unlikely to be an organic practical eg. reflux= because they take too long to carry out- not enough time in exam.
Are people going to revise group 2 stuff?
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Joy_A
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My chem teacher gave us 2 practicals to practice both in which involved the redox titration involving Fe. Thing is he mentioned that he was told what our actual practical exam involves and i have a distinct feeling that its involving redox titration but i doubt its going to have anything to do with % purity.

Anyone have any ideas about what sort of questions it can ask which involve redox titrations but dont ask about % purity???
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shyopstv
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It could ask for the concentration of a solution or the molecular mass of something
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Solid_L
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How likely is it that there will be anything about Hess's law and rate determining steps?

And for the above question... it could be to find out oxidation numbers and stoichionmetric coefficients... as well as working out the available chlorine in bleach etc.
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mysteryman
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I owuld revise hess law and kinetics etc just to make sure but i doubt it will be on this. Although they could slot a sneaky question in on this.
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alc6490
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kk
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sul1987
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#20
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so whats everyone thinking then? a redox titration to do with half equations etc? has anyones teacher hinted to them what its on? doubt it will be hess' law as this came up in the AS practical. ahhhh really nervous about this one, really need to do well in it to stand a chance of getting into university. any help would be greatly appreciated, thanks
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