The Student Room Group

This discussion is now closed.

Check out other Related discussions

OCR A2 F325: Equilibria, Energetics and Elements, 17 June 2014

Scroll to see replies

Original post by ssflcb
Could someone please help me with this question 3c(ii) on the june 2012 paper ? I don't understand how they have calculated the values for the concentrations ?
Any help would be great !


Well, the salt NaOH (at 0.05 conc) completely reacts with some of the butanoic acid and then completely dissociates. So, the concentration of the salt formed will also be 0.05. Take this 0.05 from 0.250 because obviously that much acid has been used up in the salt reaction.

So, now you have (Ka x 0.200) / 0.05 which = conc of H+. Then minus log that and you get 4.218... and the pH is then 4.22. Hope this helps :smile:
Hi can anyone help me with question 7.a)i) on the Jan 2012 paper.
I don't get why they divide 2.46x10^-5 by 4? and not 2 I don't understand what molar ratios they are using. Thanks.
(edited 9 years ago)
Can someone please help me with q7 eii on the june 2013 paper? I can't seem to balance it correctly. I'd be grateful for any help.
ImageUploadedByStudent Room1402935373.330667.jpgmethanol fuel cell what?!!!


Posted from TSR Mobile
Original post by rambo1168
ImageUploadedByStudent Room1402935373.330667.jpgmethanol fuel cell what?!!!


Posted from TSR Mobile


There's a chuck in the spec, couple of equations, advantages/disadvantages


Posted from TSR Mobile
Properties of transition metals? Is there 4


Posted from TSR Mobile
Original post by Farringtonn
There's a chuck in the spec, couple of equations, advantages/disadvantages


Posted from TSR Mobile


Yeah for a hydrogen fuel cell which is h2 + 1/2o2---> h20... This is a methanol fuel cell which I haven't come across before


Posted from TSR Mobile
Original post by Farringtonn
Properties of transition metals? Is there 4


Posted from TSR Mobile


Yes. Form complex ions, coloured compounds, used as catalysts, variable oxidation states.
Stressing over this exam way too much
Original post by chem28
I think the really hard one;

would it be 0.0285 moldm-3?

can anyone have a go to check for me?


got 0.0855 :confused::s-smilie:
Reply 1390
Avatar for Mule
Mule
6
Original post by MikeyLaa
So:
1: 2H+ + CaCO3 -> Ca2+ + CO2 + H2O
2: 2H+ + CO32- -> CO2 + H2O
3: 2H+ + MgO -> Mg2+ + H2O
4: 2H+ + 2OH- -> H2O

Iz right?


Looks good to me :smile:


Posted from TSR Mobile
Original post by BeautifulPotato
Well, the salt NaOH (at 0.05 conc) completely reacts with some of the butanoic acid and then completely dissociates. So, the concentration of the salt formed will also be 0.05. Take this 0.05 from 0.250 because obviously that much acid has been used up in the salt reaction.

So, now you have (Ka x 0.200) / 0.05 which = conc of H+. Then minus log that and you get 4.218... and the pH is then 4.22. Hope this helps :smile:


Yes it definately does ! Thankyou !
Original post by rambo1168
Yeah for a hydrogen fuel cell which is h2 + 1/2o2---> h20... This is a methanol fuel cell which I haven't come across before


Posted from TSR Mobile


Ohh. I think there's a bit in the spec about vehicles using hydrogen gas/hydrogen rich fuels ie methanol. Don't think there's much to know though


Posted from TSR Mobile
(null)wow thanks for taking the time to explain this to me, it makes sense now after all this time


Posted from TSR Mobile
Original post by periodont
Isnt h+/Ka =ha/a?

That's what the mark scheme says in June 2011 on that magic tang question...


I have seen it like that though, i dont know what is the real one

On the pH of the blood question on june 2012 I have seen it like Ka/H+ = A-/HA
(edited 9 years ago)
Original post by jamesfancourt
I have seen it like that though, i dont know what is the real one

On the pH of the blood question on june 2012 I have seen it like Ka/H+ = A-/HA


They both are. Depends what ratio you want to find


Posted from TSR Mobile
For reaction of transition metals to form precipitates are they supposed to be in square brackets, a mark scheme I saw didn't show them in square brackets and in the allow column it only had an equation with the reactant in a square bracket ?


Posted from TSR Mobile
ImageUploadedByStudent Room1402937497.826964.jpghow do u work out the ratio from this point


Posted from TSR Mobile
For the standard hydrogen half cell do we have to draw the H2 gas in the glass tube as well?
Original post by rambo1168
ImageUploadedByStudent Room1402937497.826964.jpghow do u work out the ratio from this point


Posted from TSR Mobile


That is the ratio! If that comes out as ½ the ratio is 1:2 - however you forgot a Hydrogen (CH3CHOHCOO- on top)

Related discussions

Latest

Trending

Trending

Articles for you