IAL Edexcel A2 Chemistry Unit 6 (Old syllabus)

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Reply 80

Presto

Is [Cr(H2O)6]³⁺ violet or green?

Reply 81

Presto

What organic reactions do we need to know?
All of them?

Reply 82

CuriosityYay

Original post by Presto

Is [Cr(H2O)6]³⁺violet or green?

My book says both.
But for the sake of examination stick to green

Reply 83

Presto

Thanks!

Original post by CuriosityYay

My book says both.
But for the sake of examination stick to green

Reply 84

sickomode

its better to know all the organic synthetic routes

Original post by Presto

What organic reactions do we need to know?
All of them?

Reply 85

JanaALEVEL

help
https://imgur.com/a/11TwtyD

Any prediction guys?

Better to write green

Original post by Presto

Is [Cr(H2O)6]³⁺violet or green?

Reply 88

CuriosityYay

Original post by JanaALEVEL

help
https://imgur.com/a/11TwtyD

What year/session?

Reply 89

CuriosityYay

Original post by JanaALEVEL

help
https://imgur.com/a/11TwtyD

A

nitro groups are electron withdrawing so make the ring much less reactive than the original benzene ring because less electrons are available in the delocalised system so less susceptible to electrophiles/electrophilic attacks.

Reply 90

slightly_edited

I know this name very well. Do you know me by any chance? slightly_edited used to be my Instagram account name.

Original post by saphira_jade

Then for NMR?]]]]]]]]]]]]]]

Original post by saphira_jade

We do

Reply 91

Khazard

Original post by CuriosityYay

The sign of a standard electrode potential indicates the polarity of the electrode relative to standard hydrogen electrode. This sign is fixed and doesn't change if the equation for the half-cell is reversed. Standard electrode potential is described as being a 'sign invariant quantity'.

This site says otherwise https://www.chem.wisc.edu/deptfiles/genchem/netorial/rottosen/tutorial/modules/electrochemistry/05potential/18_52.htm
and talks all about "reversing equations to that yields highest positive net emf of the cell" and " Remember that when one reverses a reaction, the sign of Eº (+ or –) for that reaction is also reversed."
and so does this site https://www.cliffsnotes.com/study-guides/chemistry/chemistry/electrochemistry/electrode-potential

(edited 4 years ago)

Reply 92

Khazard

Original post by Presto

Is [Cr(H2O)6]³⁺violet or green?

Solutions containing Cr2+ are violet/blue, but Cr3+ are green.
If you look up January 2018 question 1, you'll see the difference.

Reply 93

CuriosityYay

Original post by Khazard

My book explicitly states:

The sign of a standard electrode potential indicates the polarity of the electrode relative to standard hydrogen electrode. This sign is fixed and doesn't change if the equation for the half-cell is reversed, as sometimes stated elsewhere. Standard electrode potential is described as being a 'sign invariant quantity'.

Moreover, in the question, you subtract without changing the sign of the electrode potential.

Reply 94

JanaALEVEL

Original post by CuriosityYay

If the nitro group is withdrawing and makes nitrobenzene less susceptible to attack then why would further nitration occur ?

Reply 95

CuriosityYay

Original post by JanaALEVEL

If the nitro group is withdrawing and makes nitrobenzene less susceptible to attack then why would further nitration occur ?

It is less susceptible to electrophiles so at low temperatures only single substitution occurs and it stays as nitrobenzene but at higher temperatures double substitution occurs.