A2 OCR Chemistry B F334 - June 2015

Reply 360

MathsAddict

8

Original post by The fish inspect

Coordination number is the number of dative covalent bonds

Yeah i know that just wasnt aware EDTA4- formed 6 bonds with a central atom. If so is it always 6?

Reply 361

nats927

2

hydrolysis of amides with moderately conc naoh reflux you get a sodium salt and amine, right?

Reply 362

nats927

2

Original post by misteltain

For one of the questions they asked to draw an electrochemical cell for copper and iron. The copper electrode was copper metal but the iron was platinum. Why is that?

you use platinum when it involves molecules and ions or just ions. fe3+ and fe2_ both ions so use platinum electrode

Reply 363

MrPolish

2

Guys, get a good night sleep, wake up early in the morning tomorrow, go for a walk or quick gym/ come back, go over the notes for the last time, and then smash this exam :smile:

Reply 364

The fish inspect

2

Original post by MathsAddict

Yeah i know that just wasnt aware EDTA4- formed 6 bonds with a central atom. If so is it always 6?

They only mention edta4- so it will be six coordinate bonds. They shouldn't be cruel and use a different charge. You'know the bas***ds at OCR

Reply 365

The fish inspect

2

Original post by MrPolish

Guys, get a good night sleep, wake up early in the morning tomorrow, go for a walk or quick gym/ come back, go over the notes for the last time, and then smash this exam :smile:

I've always been told not to revise on the day of the exam,

Reply 366

pinkgorilla

5

Original post by misteltain

There was a past paper question asking you to name an ether though so I wouldn't risk it. It's straightforward anyway.

How do you name ethers ?

Posted from TSR Mobile

Reply 367

misteltain

16

Original post by pinkgorilla

How do you name ethers ?

Posted from TSR Mobile

If you google it you should get plenty of resources, I'm not that great at explaining organic nomenclature. But basically it's -oxy -ane, the shorter part of the carbon chain is the oxy e.g. methoxy and the longer part is the -ane e.g. ethane = methoxy ethane.

Reply 368

anni101

3

Original post by The fish inspect

I've always been told not to revise on the day of the exam,

same it stressed u out more, but skimming over notes for recap should be fine.Its the learning thats the issue

Reply 369

qwepoizxcmnb

4

Hey does anyone know what's going on in Jun 2013 4aiii) (with the 2 step hydrolysis question about the rate determining step). http://www.ocr.org.uk/Images/175448-question-paper-unit-f334-01-chemistry-of-materials.pdf

I looked at the solution in the mark scheme but it doesn't seem to explain very convincingly. If you look at http://www.chemguide.co.uk/physical/basicrates/ordermech.html,
near the bottom of the page, there's a section describing how to deal with a multi-step reaction with equilbrium.

But if you look at the exam question from F334, surely you'd have Kc = [H3O+][OH-] / [H2O]^2, and since [OH-] = [H3O+], [OH-]^2 = Kc[H2O]^2, so taking square roots [OH-] is proportional to [H2O] and so plugging that back into the slow step, surely overall it should be first order with respect to [H2O]?

(edited 8 years ago)

Reply 370

Shostakovish

12

so its 4:00am and im still not ready

Reply 371

kingcobra007

2

Original post by qwepoizxcmnb

Hey does anyone know what's going on in Jun 2013 4aiii) (with the 2 step hydrolysis question about the rate determining step). http://www.ocr.org.uk/Images/175448-question-paper-unit-f334-01-chemistry-of-materials.pdf

I looked at the solution in the mark scheme but it doesn't seem to explain very convincingly. If you look at http://www.chemguide.co.uk/physical/basicrates/ordermech.html,
near the bottom of the page, there's a section describing how to deal with a multi-step reaction with equilbrium.

But if you look at the exam question from F334, surely you'd have Kc = [H3O+][OH-] / [H2O]^2, and since [OH-] = [H3O+], [OH-]^2 = Kc[H2O]^2, so taking square roots [OH-] is proportional to [H2O] and so plugging that back into the slow step, surely overall it should be first order with respect to [H2O]?

It's because the rate determining step is directly determined by the products in the first equation, and two H2O molecules are needed to produce 1 OH- so H20 has double the effect on the rate determining step than CH3Cl, if that makes sense?

Reply 372

tealover96

15

Can someone please explain how cis- trans isomerism occurs when there are two chiral carbons

Reply 373

KateGeoghegan

Original post by misteltain

For one of the questions they asked to draw an electrochemical cell for copper and iron. The copper electrode was copper metal but the iron was platinum. Why is that?

It's because for the redox reaction for iron is between fe2+ and fe3+ therefore neither can form a electrode because they are ions. So you use a platinum electrode in a similar mechanism to the standard hydrogen cell

Reply 374

docdoc02

2

Original post by MathsAddict

Its like trying to put your left hand and right hand which are mirror images of each other. Put them on top of each other they can't fit in to each other they are non-superimposable.

but how does that make glycine superimposable :/

Reply 375

BrokenS0ulz

3

Original post by tealover96

Can someone please explain how cis- trans isomerism occurs when there are two chiral carbons

Which question is this referring to?

Reply 376

tealover96

15

Original post by BrokenS0ulz

Which question is this referring to?

June 13 3d
I'm not sure exactly when this occurs so the way I asked the question is likely wrong

Reply 377

BrokenS0ulz

3

Original post by tealover96

June 13 3d
I'm not sure exactly when this occurs so the way I asked the question is likely wrong

Yeah normally, chiral molecules wouldn't show cis-trans isomerism because they are usually just alkanes, so can freely rotate around the C-C bond. The reason this shows cis-trans isomerism is because the ring structure stops the C-C from rotating. Imagine if you created a ring of 6 carbons with a modelling kit, you wouldn't be able to twist the carbons around without snapping the bonds.

Reply 378

tealover96

15

Original post by BrokenS0ulz

Yeah normally, chiral molecules wouldn't show cis-trans isomerism because they are usually just alkanes, so can freely rotate around the C-C bond. The reason this shows cis-trans isomerism is because the ring structure stops the C-C from rotating. Imagine if you created a ring of 6 carbons with a modelling kit, you wouldn't be able to twist the carbons around without snapping the bonds.