Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread

Original post by Wunderbarr

Would anyone kindly give a good but simple (Edexcel) definition of oxidation state/number ? The one with the bit about being an ion?

Oh wait, I forgot to attach the question

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Reply 1842

Franckenstar

[QUOTE=:D [excludedFace]smile[/excludedFace];65990169]can someone explain to me why the answer to Q3 of JUNE 14R is D.

Most negative electrode on the left hand side by convention so surely on the right it should be a more positive value las E RHS- E LHS.

Reply 1843

:D :)

1

Original post by C0balt

RHS-LHS=emf

yeah but can you explain it in terms of oxidation reduction. Because if the cells were the other way round that method wouldn't work

Reply 1844

keres

Original post by Z.e.e

Al(OH)4-

Mathematically speaking, try this

x + (-4) = -1 where x is the oxidation state of Al and -4 is the oxidation state of OH

x is 3

Thank you, and Don Pedro too
I knew Edexcel fried my brain with c3 already haha

Reply 1845

Wunderbarr

16

Original post by sayshay

Oh wait, I forgot to attach the question

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Ok thanks!

Although it spawns the question of whether "bonding electrons" would be suitable since transition elements have multiple oxidation states.

Reply 1846

Whizbox

7

Original post by sayshay

Oh wait, I forgot to attach the question

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Which paper is this?

Reply 1847

RUNSran

Can anyone help ?
what I did was worked the out number of of moles of Cr2+ in the 250 cm^3 by dividing the 2.66 x 10^-3 by 10. I then used the equation involving the oxidation of Cr2+ to Cr3+ by Mno4 - to find the number of moles of Mno4 that will react with the cr2+ to changed it to cr3+ . so I got 5.32 x10 ^-5 for the moles of Mno4 thats needed to change cr2+ to cr3+, then I thought that changing Cr2+ to cr3+ involve increase in 1 oxidation state so in changing cr2+ to cr+6 I will need 4 times the moles of Mno4 but the answer I got using this method is only worth 3 marks ?

Reply 1848

Original post by Franckenstar

No because you need to keep it under hydrogen atmosphere as oxygen in the air will oxidize cr2+ to cr3+

It's a nitrogen atmosphere (inert).

Reply 1849

Guys how would you draw the displayed structure of nitrobenzene?
It looks like the nitrogen forms 5 bonds (two with each oxygen and one with the benzene ring), but if that's the case, shouldn't it have a charge? :/

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Reply 1850

Original post by Whizbox

Which paper is this?

June 2013 R

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Reply 1851

genevievelaw

3

anyone got a copy of jan 16 IAL paper + mark scheme + report? :biggrin:

would be appreciated

Reply 1852

Blazyy

3

Gonna get a few hours sleep.
I'll revise after suhoor.

Good luck everyone, may the odds be ever in your favour.

Reply 1853

Someone explain why it's C please?

Reply 1854

Wunderbarr

16

Original post by sayshay

Guys how would you draw the displayed structure of nitrobenzene?
It looks like the nitrogen forms 5 bonds (two with each oxygen and one with the benzene ring), but if that's the case, shouldn't it have a charge? :/

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There are some few ways of drawing it from my travels.

But generally I've seen the N having a positive charge and then single bond O with a negative charge.

Reply 1855

Original post by sayshay

Guys how would you draw the displayed structure of nitrobenzene?
It looks like the nitrogen forms 5 bonds (two with each oxygen and one with the benzene ring), but if that's the case, shouldn't it have a charge? :/

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Look it up on Google; the N has a + charge and the O has a - charge apparently!

Reply 1856

imnoteinstein

https://a5c076379da85d2c0b501a60f1a40f8eeaf5f812.googledrive.com/host/0B1ZiqBksUHNYdEFJbUVsVUl3Ums/June%202014%20QP%20-%20Unit%205%20Edexcel%20Chemistry.pdf

Q19ai) HOW do we know that the water from combustion is being measured?! theres no experiment outlined? And why is it unreasonable to assume that water could react with A??

Reply 1857

https://56leomessiphotoshop.blogspot.co.uk/p/edexcel-january-2016-exam-materials.html

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Original post by genevievelaw

anyone got a copy of jan 16 IAL paper + mark scheme + report? :biggrin:

would be appreciated

Reply 1858

Do all amino acids exist as zwitter ions in pH 7? The MC in June 14 asked what alanine would look like in pH 7...unless we're meant to know that the isoelectric point of alanine is pH 7?

Reply 1859

MacroniCheese