Official A2 OCR Chemistry Practical Thread

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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?

Reply 21

Talya

How could they ask stuff about enthalphy change? OMG I haven't revised that. Just all the organic tests and titrations...

Reply 22

sul1987

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!

Reply 23

okayyehrite

yeh same here..i doubt there will be an enthalpy change..its is highly unlikely! all my teachers have said its a titrations!

Reply 24

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".

Reply 25

mysteryman

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.

Reply 26

Aired

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.

Reply 27

okayyehrite

how u meant to work z out?

Reply 28

dontcallmeagod

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:

Reply 29

jessycat

im really scared i havent learnt any of the transition metal tests does any1 no what we have to no there?

Reply 30

okayyehrite

i dun think there is any..my teach made it clear that the only tests that are going to be asked are organic tests!

Reply 31

Joy_A

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

Reply 32

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.

Reply 33

shyopstv

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

Reply 34

Joy_A

Aired

Would we need to know the colours of the transition metal complexes??

Reply 35

nielsen94

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.

Reply 36

Aired

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)

Reply 37

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?

Reply 38

BellaNotte

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?