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

Reply 2980

TOMWIGHT

Hi has anyone got the 2015 F325 mark scheme??

Reply 2981

KB_97

10

Can someone help me with this question please?

Reply 2982

Magicalgeofray

4

Original post by TOMWIGHT

Hi has anyone got the 2015 F325 mark scheme??

Is the paper floating about also??

Reply 2983

lai812matthew

10

Original post by Dinasaurus

I thought any transition metal could give any complex?

Posted from TSR Mobile

like there is only [Fe(NH3)4(H2O)2]n+ complexes but not [Fe(NH3)6]n+ complexes.

Reply 2984

suibster

3

Original post by KB_97

Can someone help me with this question please?

feo4^2-

There's not much to explain as you kinda just have to remember that feo4 is ferrate ion and it says the charge of iron in the ion is 6+

Reply 2985

Roses98

1

Original post by mamounaltayeb

ImageUploadedByStudent Room1466527008.813326.jpg

Can someone explain this

Posted from TSR Mobile

The student is implying that a weak acid will react less than a strong acid because it has less H+ ions, i.e.: it would form less salt and water than a reaction with strong acid and alkali.

However this is not true. All acids react with alkalis regardless of whether the acid is weak or strong. All the acid will react with a given alkali (given its moles are not limiting). However, the only difference is that a strong acid starts off with a greater amount of H+ in solution because it dissociates completely, but a weak acid only has a small amount of dissociation (less H+ conc in solution). But, as the reaction proceeds, the H+ will be used up in reaction causing it's concentration to decrease. By Chateliar's principle, the weak acid would dissociate more to oppose change of reduced H+. Therefore, all the weak acid will eventually dissociate and react with alkali.

Weak acids just take longer to react, but the reaction is the same. Hence why the student is incorrect with their statement.

Hope this helps!! :smile:

Reply 2986

nuttynatty999

Any predictions for tomorrow?

Reply 2987

Serine Soul

18

Original post by KB_97

Can someone help me with this question please?

What oxidation state of iron can we associate with red?
Ignore that read it wrong
What does VI mean?

(edited 7 years ago)

Reply 2988

Roses98

1

Original post by Magicalgeofray

Is the paper floating about also??

I've attached F325 June 2015 official paper and mark scheme for those of you all that are asking :smile:

F325_-_EXAM_PAPER__Jun_2015_.pdf529.7KB

F325_-_Markscheme__Jun_2015_.pdf641.1KB

Reply 2989

lai812matthew

10

Original post by KB_97

Can someone help me with this question please?

ferrate (VI). fe have od of 6. total charge= -2. 6+n= -2, n= -8, one oxygen charge: -2.
-8/-2 =4. feo4 2- confirmed.

Reply 2990

Magicalgeofray

4

Original post by Roses98

I've attached F325 June 2015 official paper and mark scheme for those of you all that are asking :smile:

Cheers boi

Reply 2991

ToLiveInADream

17

Original post by sunsri101

I did that question and got 0.013 mol/dm^3. I'm pretty sure the answer is wrong by 1 d.p.

I got the same, don't understand the ms

Reply 2992

asunny465

3

Please can someone explain why you multiply the solar energy by 6? Im really confused
Please dont say becausr theres 6 moles of co2 reacting

DeltaH= -q/n
To figure out moles you do, -q/deltaH
I dont understand why you need to multiply the solar energy by 6.
Does it somehow imply that the solar energy is only for 1 mole of co2?

Attachment not found

Screenshot_20160621-182816.png86.7KB

Screenshot_20160621-182812.png151.8KB

Reply 2993

lai812matthew

10

Original post by asunny465

Please can someone explain why you multiply the solar energy by 6? Im really confused
Please dont say becausr theres 6 moles of co2 reacting

DeltaH= -q/n
To figure out moles you do, -q/deltaH
I dont understand why you need to multiply the solar energy by 6.
Does it somehow imply that the solar energy is only for 1 mole of co2?

Attachment not found

glucose for photosynthesis

Reply 2994

megafidget

1

One thing that's always confused me is, if you got an octahedral complex with 2 monodentates and 2 bidentates, then in the trans form, is there still optical isomerism? I know the cis form definitely does but since this molecule is symmetrical, it doesn't seem to make sense to be considered a 'separate' optical isomer.

Reply 2995

Roses98

1

Original post by Serine Soul

What oxidation state of iron can we associate with red?
Ignore that read it wrong
What does VI mean?

I don't think the red colour is what's useful to deduce the formula. The VI is the critical information. It tells you about the oxidation state of Fe. VI means +6. Plugging this in and considering the overall -2 charge should help you work it out.

If the question were to say IV or V, you can deduce that Fe would be +4 or +5 oxidation state respectively. :smile:

Reply 2996

tcameron

19

Original post by KB_97

Can someone help me with this question please?

FeO42-

because Fe has to be +6 charge
Oxygen is usually -2 and the only way to make the overall charge at 2- is to to (4x-2) + 6

Reply 2997

mechanism

5

Do we have to know about half neutralisation?

Reply 2998

RayMasterio

3

Original post by megafidget

One thing that's always confused me is, if you got an octahedral complex with 2 monodentates and 2 bidentates, then in the trans form, is there still optical isomerism? I know the cis form definitely does but since this molecule is symmetrical, it doesn't seem to make sense to be considered a 'separate' optical isomer.