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# ocr a f325 revision thread watch

1. (Original post by master y)
u're right. where is this q from/?
Questions from the textbook
2. (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
3. Thanks
4. (Original post by master y)
no need to be rude!
He was acting like a smart ass
5. (Original post by otrivine)
oh I see, so its Ka in other words
Nope , Ka is for acids
6. (Original post by chignesh10)
Nope , Ka is for acids
and for water its ionic product, Kw
7. (Original post by otrivine)
and for water its ionic product, Kw
yup
8. How would you define neutral? Is it where the concentration of H+ =OH- ?
9. (Original post by Theafricanlegend)
He was acting like a smart ass
Rude!!! Meany!! Eww
10. (Original post by otrivine)
How would you define neutral? Is it where the concentration of H+ =OH- ?
Yep

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

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12. 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 ?
13. can some help with january 11 Q3 E

http://www.ocr.org.uk/Images/65361-q...d-elements.pdf
14. (Original post by tsr1994)
Does anyone know if we have to memorise the transition metal ion colours on page 205 (Heinemann)

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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.
15. 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
16. (Original post by scorpio22)
can some help with january 11 Q3 E

http://www.ocr.org.uk/Images/65361-q...d-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
17. (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
18. (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
19. (Original post by Better)
Rude!!! Meany!! Eww
Stop being a little ***** about it
20. (Original post by Theafricanlegend)
Stop being a little ***** about it
are you going to imperial?

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