OCR B F335 - Chemistry by Design - 13th June 2012

You need to rearrange the equation to make [CO₂] the subject as that's what you're trying to work out.
All the information you need is given to you apart from [H⁺] which will need to be calculated by using the formula for pH.

Then just substitute all the values in and you should get 2.21 x 10^-3

Try it and see if you get the right answer, if not, check the spoiler

These papers are so synoptic, that's what's catching me out... I'll be fine with all the stuff I've just learnt and then suddenly something I haven't done for a year will pop up >_<

that's one benefit of revising for retakes, so glad I did.

Thank you so much, makes much more sense now.

iloveyou

Can someone post some questions which I can answer? Thank you.. physics and chemistry are hurting me now ugh

jst 3 quick questions
do we still need to know how to make expressions for solubility of a product (Ksp) or is that only old spec| and do we need to be able to use avagadros constant to calculate solubility or is that also part of old spec??

lastly, do we need to know how to calculate enthalpy of vaporisation?

To all of first paragraph, no. Note that you also don't need to know how to calculate Kp (pressures).

As for the last paragraph I'm not sure.

Does anyone know how to work out 3b (ii) on the 2010 paper? Here's a link to the paper: http://pdf.ocr.org.uk/download/pp_10_jun/ocr_57559_pp_10_jun_gce_f335.pdf?

If anyone could show me it'd be appreciated. I keep on getting an answer of 2 x 10^-28, but the mark scheme says the answer is 4 x 10^-20.

Thanks.

Does anyone know how to work out 3b (ii) on the 2010 paper? Here's a link to the paper: http://pdf.ocr.org.uk/download/pp_10_jun/ocr_57559_pp_10_jun_gce_f335.pdf?

If anyone could show me it'd be appreciated. I keep on getting an answer of 2 x 10^-28, but the mark scheme says the answer is 4 x 10^-20.

Thanks.

((conc of B) x moles of B ) x ((conc of C) x moles of C) / ((conc of A) x moles of A)

i think you just forgot to times the concentration by the moles

Does anyone know how to work out 3b (ii) on the 2010 paper? Here's a link to the paper: http://pdf.ocr.org.uk/download/pp_10_jun/ocr_57559_pp_10_jun_gce_f335.pdf?

If anyone could show me it'd be appreciated. I keep on getting an answer of 2 x 10^-28, but the mark scheme says the answer is 4 x 10^-20.

Thanks.

((conc of B) x moles of B ) x ((conc of C) x moles of C) / ((conc of A) x moles of A)

i think you just forgot to times the concentration by the moles

Kc = [CO]^2 x [O2] / [CO2]^2

You're given these values, so;

Kc = (2x10^-8)^2 x (1x10^-8) / (1x10^-2)^2

= 4 x 10^-20

I hope you can read that okay, not entirely sure how to do super and subscript on the forum!

$K_c = \frac{[CO]^2[O_2]}{[CO_2]^2}$

can you see why now?

EDIT: You are actually correct, 4x10^-20 is correct. Look at the ms.




no. Raise it to the power of the mole, don't multiply.

bro do the january 2006 2854 paper, and tell me if you find it harder than all other pastpapers