OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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With electrophilic substitution, with the intermediate why does the nitrobenzene or halobenzene form instead of reforming benzene??

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It's how the universe works.

If I had to guess, it would be because the substituted group and the benzene ring have a greater attraction for the electrons than the hydrogen atom does. Hydrogen atoms have a much lower electronegativity than something like chlorine atoms, which explains the polarity of HCl and hydrogen bonding etc.

(edited 7 years ago)

Reply 421

thad33

Original post by Serine Soul

Yeah that's what I do.
Have people memorised the electron configurations for the ions of Sc and Zn, or do you just go with it, knowing Sc3+ and Zn2+ are the only ions that form?

What do you mean? I just work out each one systematically

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Reply 422

username986184

Original post by Saywhatyoumean

With electrophilic substitution, with the intermediate why does the nitrobenzene or halobenzene form instead of reforming benzene??

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http://web.usm.my/chem/LECTURER/KOT222/KOT222_Chap_17.pdf
Slide 5

http://chemwiki.ucdavis.edu/Core/Organic_Chemistry/Hydrocarbons/Arenes/Synthesis_of_Arenes/Electrophilic_Aromatic_Substitution

Reply 423

Serine Soul

Original post by thad33

What do you mean? I just work out each one systematically

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That's what I mean :tongue:

Reply 424

AqsaMx

Could anyone explain the formation of H2 gas? I don't understand the MS answer

Reply 425

Serine Soul

Original post by AqsaMx

Could anyone explain the formation of H2 gas? I don't understand the MS answer

OH- ----> H2

OH- ----> O2

How can you fill in the gaps?

Not + 4HCl, but 4Cl-

You can write out an equation with HCl:

[Cu(H2O)6]2+ + 4HCl ----> [CuCl4]2- + 6H2O + 4H+ (I think this is correct, someone please correct me if not)

Reply 428

username986184

Original post by AqsaMx

Could anyone explain the formation of H2 gas? I don't understand the MS answer

Here

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Reply 429

AqsaMx

Original post by TeachChemistry

Here

Thank you

Reply 430

AqsaMx

Original post by Serine Soul

OH- ----> H2

OH- ----> O2

How can you fill in the gaps?

That's how I was trying to work it out but I was confused as to why the OH- and H2 were on the same side but I get it now :smile:

Reply 431

AqsaMx

Attachment not found

Can anyone explain this step by step? And why you divide the enthalpy change by the energy taken up??
Thank you :smile:

image.jpg277.0KB

Reply 432

username986184

Original post by AqsaMx

Attachment not found

Can anyone explain this step by step? And why you divide the enthalpy change by the energy taken up??
Thank you :smile:

Here

image.jpeg158.5KB

Reply 433

username986184

Q tells you ferrate VI is an oxidising agent. So what in KI is oxidised. What would you SEE with your eyes?

Reply 434

username986184

To start with yes it would go brown due to oxidation of iodide ions to iodine. It then may become colourless again as the iodine is oxidised to iodate ions.

EDIT:
On reflection the mixture could go brown also due to the formation of iron III oxide. We really need to know more about the reduction potentials of all the possible intermediates.

(edited 7 years ago)

Reply 435

pineneedles

Just going through the specification and it says ' explain the water solubility of carboxylic acids in water in terms of hydrogen bonding and dipole/dipole interaction. Im unsure what dipole dipole interaction it means? I've drawn a diagram of what I think it looks like. If you had a question asking about the solubility if carboxylic acids in water would you need to discuss both factors?

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Reply 436

username986184

Original post by pineneedles

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Not being funny but that is defo not the way to represent a hydrogen bond. I went to an event at Warwick Uni last year where a chief examiner said EXACTLY what they wanted from students here. I will find the slide.

Reply 437

username986184

Original post by pineneedles

Slides 31-33 or thereabouts

Warwick-2015-1.pptx1691.5KB

Reply 438

pineneedles

Original post by FutureMedic97

I think you have the bonds the wrong way round, hydrogen bonding occurs when the hydrogen atom is attached to an electronegative atom like oxygen or nitrogen
There is a dipole on C=O (permanent dipole) and so it will form pd-pd bonds

Hmm, no I think that's right even if drawn badly. I though hydrogen bond is an attraction between a partially positive hydrogen and lone pairs of electrons on oxygen/nitrogen/fluorine

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