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OCR B (Salters) F332 Tuesday 4th June 2013 Exam Discussion (Now Closed)

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Are these correct exam definitions:

Electrophile is positively charged and bonds by accepting a pair of electrons

Nucleophile is negatively charged and has a lone pair of electrons which can be donated to form a covalent bond.

I always make sure to say that an electrophile is a positively charged species that is attracted to areas of high electron density, and can form a covalent bond by accepting a lone pair of electrons

Reply 361

krisshP

Original post by AGKhan

How would you explain why ozone has a bond angle of 117°? It has a dative bond and a double bond as well as a lone pair which is putting me off when describing it!
Thankss :smile:

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Dunno what dative bond you are on about.

http://www.google.com/search?client=tablet-unknown&hl=en&authuser=0&site=imghp&tbm=isch&q=ozone+molecule+lewis+structure&revid=39960984&sa=X&ei=mAGrUe-SCPKm0wXVyYGoDw&ved=0CDYQ1QIoAA&biw=768&bih=1024

Around central O atom there are 3 areas of electron density which repel one another s far apart as possible. Hence ozone has a V shape with a bond angle 118.5*.

120-2.5*=118.5* due to 1 lone pair squeezing bond angle by 2.5* per lone pair.

(edited 10 years ago)

Reply 362

Jlane5000

Could some kind person please explain the mark scheme for June 2011, question 4 (d) (i) to me? In the question it asks how to turn methanol into chloromethane. I thought that to turn an alcohol into a chloroalkane that you shake with conc HCl at room temp. However the mark scheme says it is HCl and heat/high temp. I really don't understand where they got that from :confused:

Reply 363

krisshP

Original post by Jlane5000

I always make sure to say that an electrophile is a positively charged species that is attracted to areas of high electron density, and can form a covalent bond by accepting a lone pair of electrons

But I don't think it says that in the mark schemes. Sorry, it's just that I want to be concise to save precious exam time.

Reply 364

krisshP

Original post by Jlane5000

I always make sure to say that an electrophile is a positively charged species that is attracted to areas of high electron density, and can form a covalent bond by accepting a lone pair of electrons

Yeah you are right. It says on Wikipedia attracted to an electron rich centre. It would be good to say it to be on the safe side.

Thanks

Reply 365

Jlane5000

Original post by krisshP

Yeah you are right. It says on Wikipedia attracted to an electron rich centre. It would be good to say it to be on the safe side.

Thanks

No worries, and it does come up in some of the mark schemes, otherwise i wouldn't put it down myself :wink:

Reply 366

King Hotpie

Original post by krisshP

Presumably the mark scheme would allow 120*, as that is what we are taught for 3 areas of electron density without looking it up on line?

Reply 367

Branny101

Original post by King Hotpie

Presumably the mark scheme would allow 120*, as that is what we are taught for 3 areas of electron density without looking it up on line?

This is what i'd've thought, one double-bond, one dative and one lone is what we were taught?

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Reply 368

krisshP

Original post by Jlane5000

No worries, and it does come up in some of the mark schemes, otherwise i wouldn't put it down myself :wink:

The mark schemes are so weird. Like mostly they accept saying high frequency UV, then there's one where they only accept high energy UV

Reply 369

Jlane5000

Original post by krisshP

The mark schemes are so weird. Like mostly they accept saying high frequency UV, then there's one where they only accept high energy UV

I know I hate how they can just change their minds each year :rolleyes:

so definitely best to cover all your bases, put it down even if its only been in a few of the mark schemes :biggrin:

Reply 370

Welbeck

Do you need to remember planck's constant?

Reply 371

Willszz1

(u) describe in outline the preparation of a chloroalkane from
an alcohol using HCl:

What is this specifically asking for? It's probably something simple but I've never seen something that asks for the preparation of chloroalkane etc

Is it just like ch3cl+ h20 -> ch3oh+ hcl? Or something else

Reply 372

diggerz

Original post by Willszz1

i believe it is asking for the technique if its 3 marks or more so how you shake it with sodium hydrogen carbonate to remove acidic impurities then run off the chloroalkane layer and add anhydrous sodium sulfate to remove water then it is purified by distillation :smile:

Reply 373

krisshP

Original post by Welbeck

Do you need to remember planck's constant?

Nope

Reply 374

Welbeck

Depletion of Ozone
Cl• + O3 ---> ClO• + O2
ClO• + O3 ---> Cl• + 2O2
Overall:O+ O3 --> 2O2
or
Cl• + O3 ---> ClO• + O2
ClO• + O ---> Cl• + O2
Overall: 2O3 ---> 3O2

Which one is right? I thought it would be the top one?
Also how do you work out the overall reaction?

Reply 375

AGKhan

Original post by krisshP

It has a dative bond and a double bond but I think the pi bond from the double is shared. I tried reading up on it online and many places say the bond angle is 116.8° (116.78°)

Reply 376

krisshP

Original post by AGKhan

It has a dative bond and a double bond but I think the pi bond from the double is shared. I tried reading up on it online and many places say the bond angle is 116.8° (116.78°)

It does NOT matter what bond it is. The main thing is it being an AREA of electron density.