ocr a f325 revision thread

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Reply 1680

ofudge

Original post by master y

u're right. where is this q from/?

Questions from the textbook :smile:

Reply 1681

otrivine

Original post by KD35

You talking about the ionic product of water?

If you are, it's similar. ka= [OH-][H+]/[h2O]
As H2O is constant, they move it to other side and KAx[H2O]=Kw=[OH-][H+]

oh I see, so its Ka in other words

Reply 1682

otrivine

Original post by master y

http://lmgtfy.com/?q=ionisation+constant

heehee

Thanks

Reply 1683

Theafricanlegend

Original post by master y

no need to be rude!

He was acting like a smart ass

Reply 1684

chignesh10

Original post by otrivine

oh I see, so its Ka in other words

Nope , Ka is for acids

Reply 1685

otrivine

Original post by chignesh10

Nope , Ka is for acids

and for water its ionic product, Kw

Reply 1686

chignesh10

Original post by otrivine

and for water its ionic product, Kw

yup

Reply 1687

otrivine

How would you define neutral? Is it where the concentration of H+ =OH- ?

Reply 1688

Better

Original post by Theafricanlegend

He was acting like a smart ass

Rude!!! Meany!! Eww :angry:

Reply 1689

tsr1994

Original post by otrivine

How would you define neutral? Is it where the concentration of H+ =OH- ?

Yep

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Reply 1690

tsr1994

Does anyone know if we have to memorise the transition metal ion colours on page 205 (Heinemann) ImageUploadedByStudent Room1370775239.985207.jpg

ImageUploadedByStudent Room1370775239.985207.jpg

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Reply 1691

dwindledStrangly

For questions asking to show the typical reactions of transition elements and the reactions, for the redox equation is writting:

'Mno4- + 8H+ + 5e- > Mn2+ + 4H2O
Purple > Colourless'

Suffcient or should you include write a whole equation of for example when it oxdises Fe2+ > Fe3+.

And quick question or everyone can you suggest the rest of the typical reactions of transition elements ?

Reply 1692

scorpio22

can some help with january 11 Q3 E
its giving me a headache.

http://www.ocr.org.uk/Images/65361-question-paper-unit-f325-equilibria-energetics-and-elements.pdf

Reply 1693

dwindledStrangly

Original post by tsr1994

Does anyone know if we have to memorise the transition metal ion colours on page 205 (Heinemann) ImageUploadedByStudent Room1370775239.985207.jpg

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You wouldn't need to know it. Just the facts that:
Sc and Zn form colourless compounds becuase they form ions with complete d-orbitals.
That Mn2+ is pale pink but appear colourless in solution.(because water is in excess) Mn7+ is purple which causes the purple colour of MnO4-.
And finally not a must but from A/S u may need to know Cr6+ (from Cr2O72-) is orange, and Cr3+ is green.

(edited 10 years ago)

Reply 1694

s24a

would anyone be able to explain conjugate acid-base pairings? i still can't seem to work out which of the two reacting acids is more likely to act as a base

Reply 1695

DudeBoy

Original post by scorpio22

can some help with january 11 Q3 E
its giving me a headache.

http://www.ocr.org.uk/Images/65361-question-paper-unit-f325-equilibria-energetics-and-elements.pdf

This question is pretty simple, it is just about applying your knowledge which is difficult.
It tells you each disulfide is broken down by 2 thioglycate ions to form 2 R-S-H and something else.
SO:
R-S-S-R + 2HSCH2COO- --> 2 R-SH and ?

Now try to balance them out:
They H must be taken from HSCH2COO-
So you would get 2SCH2COO-
Now you know that S can form disulfide bridges so:
-OOCCH2S-SCH2COO-

Part duex:
H2O2 must reach with the R-SH to rebuild the bridges
H2O2+2R-SH --> R-S-S-R + ?
Look at what has changed
H2O2+2H--> 2H2O

Reply 1696

Theafricanlegend

Original post by s24a

would anyone be able to explain conjugate acid-base pairings? i still can't seem to work out which of the two reacting acids is more likely to act as a base

Lower ka more likely to act like a b

Reply 1697

DudeBoy

Original post by s24a

would anyone be able to explain conjugate acid-base pairings? i still can't seem to work out which of the two reacting acids is more likely to act as a base

Usually gives the Ka values, the higher Ka is the acid. If not, as a general rule
Nitric acids and Halogeno acids (HNO3, HCl, HF ect ) are more acid than Carboxylic.
The shorter the carboxylic acid the more acidic so COOH > CH3(CH2)7COOH