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

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Original post by Ezexamsalltheway

HI , guys how many of the transition metal aqueous ion colours do we actually need to know. all of them? thought i should better start my revision now :P rip

Copper
(Blue) Cu²⁺or [Cu(H2O)₆]²⁺
(Light blue) Cu(OH)₂ (s)
(Yellow) [CuCl₄]^2-(this one looks green if you don't have excess Cl^-
(Deep blue) [Cu(NH₃)₄(H₂O)₂]²⁺

Spoiler

Cobalt
^{(Pink) Co²⁺}
(Blue) [CoCl₄]^2-
(Blue) Co(OH)₂

Spoiler

Iron
(Pale Green) Fe²⁺
(Green) Fe(OH)₂
(Yellow) Fe³⁺
(Brown) Fe(OH)₃

Chromium (as in alcohol oxidation reactions)
(Green) Cr³⁺
(Orange) Cr₂O₇^2-

Manganese
(Purple) MnO₄^-
(Pink, colourless) Mn²⁺

And the colour changes with thiosulfate and iodine in the clock reaction. Not transition elements, but useful to know.

Spoiler

Reply 3001

itsConnor_

is 2nd equation so charges on right = charges on left? https://gyazo.com/7d6e8331e15fc94e20faa04b0f006cef do i have to do that with all ionic equations?

Reply 3002

megafidget

Original post by RayMasterio

Yes - you can get an optical isomer. It's literally a mirror image of the trans!

But that's the thing, the mirror image of the trans will look exactly the same as the trans...., I guess they will rotate plane-polarised light in different directions so they wouldn't be the same molecule but the molecules appear to occupy the same spaces (from the diagrams at least).

Reply 3003

garlicbread23

Original post by lai812matthew

that's what i write

do you have to be specific and say two, what if you say bacteria produced one and lab produces many i.e. more than one, do you have to specify 2

Reply 3004

M.Branson98

How do you know if an indicator is suitable for a certain acid-base titration?

Reply 3005

megafidget

Original post by ImNervous

Do we need to know anything about electrolytic cells or do we need to know both?

Posted from TSR Mobile

No optical isomers of the trans form.

No we don't need to know about electrolyte cells, yeh that's what I thought.

Reply 3006

Serine Soul

Original post by Roses98

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:

Yeah I know that.

I was asking the OP what the VI stood for? To check they understand?

I hadn't realised that they had given roman numerals when I first saw the question

Reply 3007

Dinasaurus

Original post by lai812matthew

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

Is that just memory or should we know why that doesn't occur?

Posted from TSR Mobile

Reply 3008

Dinasaurus

Original post by M.Branson98

How do you know if an indicator is suitable for a certain acid-base titration?

If the peak of the acid is high then there's a strong base, if the bottom curve is low there's a strong acid.

Indicators will have their range given so you just have to see if it falls in the range right?

Posted from TSR Mobile

Reply 3009

tcameron

Original post by mechanism

Do we have to know about half neutralisation?

what's that??

Reply 3010

KB_97

I'm so nervous for this exam. I just can't to the calculations towards the end of the paper. I'm so tired I keep making stupid mistakes. Bye bye a*

Reply 3011

mechanism

Original post by tcameron

what's that??

To do with acid and bases where HA=A-.

Reply 3012

ToLiveInADream

How would you conduct an experiment to measure enthalpy of solution (4 marks)

Reply 3013

victoria98

Original post by lai812matthew

my last attempt on A* after i flopped f324 if this doesn't go well i'll have no uni to go to.......

Same.... F324 was too wordy for me, I wanted more synthesis and a long NMR. I made many incredibly silly errors - I completely ignored the carbon-13 spectrum until I left the exam hall and realised why it was there etc.... F325 tends to go better for me. More maths = more marks haha. Good luck!

Reply 3014

tcameron

Original post by mechanism

To do with acid and bases where HA=A-.

how does that work? Why would it be only a jhalf neutralisation

Reply 3015

tcameron

Original post by ToLiveInADream

How would you conduct an experiment to measure enthalpy of solution (4 marks)

you can't measure the lattice enthalpy directly so how would that work?

Reply 3016

mechanism

Original post by tcameron

how does that work? Why would it be only a jhalf neutralisation

This is what I'm confused about, however I think I get it - when half of HA reacts, that amount of A- has been formed. so the [HA] left = [A-] formed

Reply 3017

Arima

Original post by M.Branson98

How do you know if an indicator is suitable for a certain acid-base titration?

find the pH range of the indicator - say for example it's given as 4.0 - 8.0. Then look at the curve for the acid base titration and spot the end point - so like the centre of the sharp upward line where neutralisation occurs. If the end point lies about the middle of the pH's range (so around 6.0 in this case) then it's suitable

Reply 3018

Dinasaurus

Original post by tcameron

anyone have a proper definition of Kstab? The one in the book makes no sense to me

It's basically Kc without water, the higher the kstab the more stable a complex is.

Reply 3019

Rust Cohle

Can somebody run through those standard 3 markers on energy comparisons of e.g. RbF vs RbCl or MgCl2 vs NaCl Usually accompanied by a table with some enthalpy values of hydration/solution/lattice enthalpy.