Official A2 OCR Chemistry Practical Thread Watch

shyopstv
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#21
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#21
For the last two days, my teachers have been all titration calculations this, redox reactions that. You wouldn't have thought that they would be teaching us something unrelated on purpose?
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Talya
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#22
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#22
How could they ask stuff about enthalphy change? OMG I haven't revised that. Just all the organic tests and titrations...
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sul1987
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#23
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#23
don't worry it wont be on enthalpy, i had a full AS practical on this last week so its highly doubtful, plus it has nothing at all to with the skill p so don't worry! I haven't learnt any organic tests though! got me worried! right think im going to pust most of my effort in redox titrations, seems logical according to the plan and what most people are saying!
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okayyehrite
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#24
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#24
yeh same here..i doubt there will be an enthalpy change..its is highly unlikely! all my teachers have said its a titrations!
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Aired
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#25
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#25
All you need to know for organic tests is...

Test for an aldehyde: Add Tollen's reagent (ammonical silver nitrate). A positive result is a black precipitate or silver mirror effect.

Test for unsaturation: Shake the sample with bromine water. If it is unsaturated the bromine water will be decolourised (Orange --> Colourless).

Test for a primary or secondary alcohol: Heat under reflux with acidified potassium dichromate (VI). If a primary or secondary alcohol were present, the solution will change from orange to green.

Esters: Distinctive "fruity smell".
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mysteryman
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#26
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#26
Maybe finding concentration of something using potassium dichromate, i doubt they'd do it on potassium manganate as that would be too obvious. % composition of a certain transition metal in an alloy? Probably transition metals, with test-tube tests for them maybe for 2nd part.
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Aired
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#27
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#27
You could get asked a few things based on a KMnO4 titration, i.e. reacting ratio with an unknown substance, molarity of a solution (or molarity of the KMnO4) or you could be asked to determine the final oxidation number of say "element X" in the titration...

i.e. 20cm3 0.1M Z2+ reacted completely with 40cm3 0.02M KMnO4. Find the final oxidation number of Z.
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okayyehrite
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#28
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#28
how u meant to work z out?
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dontcallmeagod
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#29
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#29
just a thought, redox equation, chemical tests. How about the oxidation of alcohols? Redox and tests!!! Colour change???!!!

Also almost definitely some kind of test involving a bunsen burner, test tubes etc....? :confused:
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jessycat
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#30
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#30
im really scared i havent learnt any of the transition metal tests does any1 no what we have to no there?
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okayyehrite
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#31
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#31
i dun think there is any..my teach made it clear that the only tests that are going to be asked are organic tests!
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Joy_A
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#32
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#32
can anyone post up all the organic tests please???......its been a long while since i've actually did some organic work...had the exam in Jan! :P
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Aired
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#33
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#33
(Original post by Aired)
All you need to know for organic tests is...

Test for an aldehyde: Add Tollen's reagent (ammonical silver nitrate). A positive result is a black precipitate or silver mirror effect.

Test for unsaturation: Shake the sample with bromine water. If it is unsaturated the bromine water will be decolourised (Orange --> Colourless).

Test for a primary or secondary alcohol: Heat under reflux with acidified potassium dichromate (VI). If a primary or secondary alcohol were present, the solution will change from orange to green.

Esters: Distinctive "fruity smell".
They're the organic tests we need to know.

For the transition metals you need to know:

Cu(II) with chloride ions and ammonia
Fe(II) with ammonia
Fe(III) with amonia, chloride ions and thiocyanate ions.
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shyopstv
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#34
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#34
Cu(II) with chloride ions and ammonia
Fe(II) with ammonia
Fe(III) with amonia, chloride ions and thiocyanate ions.

Sorry but someone please tell me what they are? I know that Cu(II) goes yellow in chlorine and deep blue in ammonia and Fe(III) goes blood red with thiocyanite but have no idea about the others..

Thanks
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Joy_A
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#35
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#35
(Original post by Aired)
They're the organic tests we need to know.

For the transition metals you need to know:

Cu(II) with chloride ions and ammonia
Fe(II) with ammonia
Fe(III) with amonia, chloride ions and thiocyanate ions.

Would we need to know the colours of the transition metal complexes??
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nielsen94
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#36
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#36
All you need to know for Fe(II) is that it reacts with ammonia to form Fe(OH)2 and the same for Fe(III). But as far as i can see, they never require particularly detailed knowledge for the prac. its the evaluation i'm much more worried about.
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Aired
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#37
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#37
Fe(II) with ammonia forms Fe(II) hydroxide (it's an acid/base reaction), Fe(II) hydroxide is a green precipitate.

Fe(III) with chlorine forms [FeCl4- which is a yellow solution.

Fe(III) with ammonia forms Fe(III) hydroxide (red/brown precipitate)
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emthebest
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#38
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#38


OMG OMG - huge news fellow chemistry pioneers! Ive just had some chemistry tutition and i asked him for some advice - my tutor said it was an enthlpy change! how f****d up is that?
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BellaNotte
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#39
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#39
(Original post by emthebest)

OMG OMG - huge news fellow chemistry pioneers! Ive just had some chemistry tutition and i asked him for some advice - my tutor said it was an enthlpy change! how f****d up is that?

If enthalpy changes comes up, i will be pissed off for the rest of the week, i hate anything to do with them :mad:

Like others, my teachers have also been going on about titrations so... hopefully. Not that they're any better either though :rolleyes:
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mysteryman
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#40
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#40
Its not enthalpy look how the person who posted that only has 1 post which is this, prob made it up to try and scare us all.
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