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Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

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Original post by SKK94
Thanks :smile:

Another doubt:
Phenylamine dissolves in aqueous acids because it forms an ionic salt (and they are more soluble in aq. acids than in water)
^Does this apply to alkyl amines as well?

I have similar doubts to yours in the transitions chapter. I'm still trying to figure them out :/


I would think so yes, since the alkyl amines are also soluble in water. I think they're much more soluble in general than Phenylamines because they don't have the hydrophobic benzene ring
Could someone have a look at question 6 in the june 2012 paper and explain it to me please? Apparently the answer is b but i dont see you it wouldnt react with 2,4 dnp as theres a c=o bond present..
Thanks!
Reply 1522
Avatar for The_Geek
The_Geek
The answer is b because 2,4 - DNP is a test for the c=o but ONLY in aldehydes and ketones! In Benzocaine the c=o bond is part of an ester group. :smile:
Original post by The_Geek
The answer is b because 2,4 - DNP is a test for the c=o but ONLY in aldehydes and ketones! In Benzocaine the c=o bond is part of an ester group. :smile:


Thank you, never realised that before!
Why are the grade boundaries so high for chemistry :no::no::no:

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Reply 1525
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AS01
12
Original post by freakynerdlol
Why are the grade boundaries so high for chemistry :no::no::no:

Posted from TSR Mobile


Ikr! for unit 1 and 2 its quite low and for unit 4 and 5 its like around 70s for an A!
hi everyone. looking for help with transition metal compounds colours, different resources give different colours.

can anyone giving me a list of the colours with - little OH/NH3 -excess OH -excess NH3 for the top row of transition metals.

mainly problem is Chromium.

*[Cr(H2O)6]3+ = green (violet on some resources)

*[Cr(NH3)6]3+ = yellow (purple on some resources)

thank you :smile:
Reply 1527
Avatar for SKK94
SKK94
1
Original post by posthumus
I would think so yes, since the alkyl amines are also soluble in water. I think they're much more soluble in general than Phenylamines because they don't have the hydrophobic benzene ring


Thanks!
Reply 1528
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AS01
12
Original post by paddyroddy
hi everyone. looking for help with transition metal compounds colours, different resources give different colours.

can anyone giving me a list of the colours with - little OH/NH3 -excess OH -excess NH3 for the top row of transition metals.

mainly problem is Chromium.

*[Cr(H2O)6]3+ = green (violet on some resources)

*[Cr(NH3)6]3+ = yellow (purple on some resources)

thank you :smile:


I have posted a PDF file one or two pages back which has the Colors and ions as well.

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Original post by JRP
The metal-aqua ion of Cr3+ is [Cr(H2O)6]3+ which is VIOLET.
Adding sodium hydroxide creates the precipitate of Cr(OH)3 which is GREEN.
Adding sodium hydroxide in excess causes the precipitate to dissolve to form [Cr(OH)6]3- which is GREEN.

Remember:

•

the initial metal-aqua ions always have H2O only as their ligands, and the charge is that of the ion.

•

the precipitate formed by NON-EXCESS NaOH (or NH3) has no charge, and has the same number of OH ligands as the charge on the transition metal ion

•

Chromium and Zinc are the only to react with EXCESS OH. They are also the only that show amphoteric behavior. The number of OH ligands is enough to make the initial metal-aqua ion charge the negative version, with the same magnitude. ([Cr(H2O)6]3+ -----> [Cr(OH)6]3-, [Zn(H2O)6]2+ -----> [Zn(OH)4]​2-)



However, remember that in the case of dichromate(VI) ions being reduced to form Cr3+ ions, the colour change is orange to green because of impurities forming with the Cr3+ ions, despite the metal-aqua ion actually being violet. I don't think you need to remember why, but just know that there are different colours used depending on the context. This is probably what got you confused.

Hope this helped :smile:


That is what got me confused, and it did help a lot! +rep :smile:
Reply 1530
Avatar for Bord3r
Bord3r
10
Grade Boundaries

June 2010 A*-73 A-66 B-59 C-53 D-47 E-41

January 2011 A*-72 A-65 B-58 C-51 D-44 E-38

June 2011 A*-73 A-67 B-61 C-55 D-49 E-43

January 2012 A*-80 A-72 B-64 C-56 D-49 E-42

June 2012 A*-73 A-67 B-61 C-55 D-49 E-43

January 2013 A*-77 A-69 B-61 C-53 D-49 E-39

The average for an:
A* is 75
A is 69
B is 61
C is 54
D is 48
E is 41

One point to make is that whilst Jan 2013 and Jan 2012 had very high boundaries esp. for the A*, the June grade boundaries have had 73 for an A* every year.
(edited 10 years ago)
Original post by Bord3r
Grade Boundaries

June 2010 A*-73 A-66 B-59 C-53 D-47 E-41

January 2011 A*-72 A-65 B-58 C-51 D-44 E-38

June 2011 A*-73 A-67 B-61 C-55 D-49 E-43

January 2012 A*-80 A-72 B-64 C-56 D-49 E-42

June 2012 A*-73 A-67 B-61 C-55 D-49 E-43

January 2013 A*-77 A-69 B-61 C-53 D-49 E-39

The average for an:
A* is 75
A is 69
B is 61
C is 54
D is 48
E is 41

One point to make is that whilst Jan 2013 and Jan 2012 had very high boundaries esp. for the A*, the June grade boundaries have had 73 for an A* every year.


This is so useful - thanks! Does anyone know approx. what 100 ums would be I raw? (Obviously estimation based on past years?)
What does everybody want/need in this paper then?
Original post by Weaselmoose
This is so useful - thanks! Does anyone know approx. what 100 ums would be I raw? (Obviously estimation based on past years?)


Judging from the averages kindly provided I would suspect 71 will get you 100 UMS :smile:


Original post by lordmackery
What does everybody want/need in this paper then?


A high B! I need a B overall for A level Chemistry :smile:
Reply 1534
Avatar for Bord3r
Bord3r
10
Original post by Weaselmoose
This is so useful - thanks! Does anyone know approx. what 100 ums would be I raw? (Obviously estimation based on past years?)


The averages would give a 120 UMS cut-off of 81 :smile:

Edit; Thanks to Weaselmoose for pointing out the error.
(edited 10 years ago)
Original post by lordmackery
What does everybody want/need in this paper then?


69 for an A or 100 for an A*
Original post by Bord3r
The averages would give a 100 UMS cut-off of 81 :smile:


Surely that's more than an A*, but an A* is 108 UMS?
Reply 1537
Avatar for Bord3r
Bord3r
10
Original post by lordmackery
What does everybody want/need in this paper then?


I need an A for university (which means I need like an E in this paper :redface:), but I want an A* which means I need 102.
Reply 1538
Avatar for Bord3r
Bord3r
10
Original post by Weaselmoose
Surely that's more than an A*, but an A* is 108 UMS?


Oops I meant 120 UMS, too many maths papers. :colondollar:
Original post by Bord3r
Oops I meant 120 UMS, too many maths papers. :colondollar:


Hah no worries

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