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

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Reply 560

Branny101

Heyy how would I go from % to pptv?

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Reply 561

tasniaa

Original post by madrevision

it depends on the equation e.g if you asked to write a half equation of the formation of chlorine molecules from chloride ions you'd get 2Cl- >Cl2 + 2e but if it was the formation of chloride ions then the half equation would be the other way around, just make sure you read the question carefully :smile:

oh I get it, thank you :biggrin:

Reply 562

madrevision

Original post by Branny101

Heyy how would I go from % to pptv?

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just divide by 100 and multiply by 10 ^12 because if you had 2 pptv - it's the same as 2/1000 000 000 000 as a percentage is 2/1000 000 000 000 x 100.
or 2pptv is 2/ 10 ^12 percentage is 2/10^12 x 100 so you just undo what you've done(i.e divide where you've multiplied) this is kinda hard to explain with large numbers.. :cool:

Reply 563

tipani

Original post by tasniaa

you know in the equilibrium questions they state H = +x or -x

how do we know which side is exo/endothermic?

It usually tells u that, the enthalpy change of the reaction e.g. is +450kJmol-1.
In this case, the forward reaction gives this enthalpy change, so the forward reaction will be endothermic, so an increase in temperature will move the position of equilibrium to the right, in the endothermic direction.

Hope this makes sense

Reply 564

super121

Original post by Davelittle

Sorry I meant the repeating unit! :smile:

Just open up the double bonds :smile:

Reply 565

tipani

Does anyone know how to represent an electron in a dot and cross diagram for an ion, if it has been electron had come from somewhere else, for instance if i said give the dot and cross diagram for a OH- ion. :confused:

Reply 566

SyedaK

Original post by madrevision

I'm confused, is it basically:
pptv to percentage /10^12 x 100
percentage to pptv is x 10^12 /100?

Reply 567

tasniaa

Original post by tipani

it does, thank you!

So say the equilibrium shifts towards the reactants, does this make more or less products?

Reply 568

tasniaa

Original post by tipani

leave the gained electron clear? like this o
but colour the rest in?

I hope that makes sense xD

Reply 569

Branny101

Original post by madrevision

Ahhhhhhhhhhhh, ty :biggrin:

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Reply 570

madrevision

Original post by SyedaK

I'm confused, is it basically:
pptv to percentage /10^12 x 100
percentage to pptv is x 10^12 /100?

yh basically (I prefer to start by dividing- by 100 to avoid confusion when you're working backwards) so you're right percentage to pptv is /100 then x 10^12 :biggrin:

Reply 571

michmic

Can anyone draw vaccum filtration for me pls??

Reply 572

carla6600

Original post by tasniaa

leave the gained electron clear? like this o
but colour the rest in?

I hope that makes sense xD

Put a square to show it came from something else

Reply 573

carla6600

Original post by madrevision

yh basically (I prefer to start by dividing- by 100 to avoid confusion when you're working backwards) so you're right percentage to pptv is /100 then x 10^12 :biggrin:

yeah but it's in parts per billion/trillion by VOLUME so it wouldn't be as simple to convert which confuses me!

Reply 574

NielsBohrsDad

In the jan 2011 paper i dont get the moles ratio question can somebody please explain it??

With steps please

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Reply 575

super121

Original post by michmic

Can anyone draw vaccum filtration for me pls??

This isn't on the spec?

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Reply 576

Davelittle

Original post by super121

Just open up the double bonds :smile:

The mark scheme has a double bond still in?

Take a look- June 2011 f332 Q 5. d) ii. I think!

Really confused :/

Reply 577

Davelittle

Original post by NielsBohrsDad

In the jan 2011 paper i dont get the moles ratio question can somebody please explain it??

With steps please

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Imagine you had 58.5g of NaCl (Mr=58.5) that would mean you have 58.5/2g of KCl (because its 2:1 ratio of the compounds)

The moles=mass/Mr so (58.5/2)/74.5=0.39 (because it asks for moles ratio)

Reply 578

Willszz1

Original post by diggerz

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:

Ohhh! Yeah I understand that. Thanks.