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Competition - post a photo you've taken of nature >>
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Competition - post a photo you've taken of nature >>

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EDEXCEL CHEMISTRY Module 4

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Reply 40
Avatar for jammie08
jammie08
I think it was out of 2, if it is you would have got a mark.
Reply 41
Avatar for jammie08
jammie08
Ah right..no I don't remember getting 48 anywhere...but that doesn't mean it's wrong, just don't remember...hmm..
Reply 42
Avatar for Fatima52
Fatima52
It was out of 3- would it not have been possible to get 1.5? lol
Reply 43
Avatar for jammie08
jammie08
Oh was it! Wierd that.
I'm not sure then, but the reaction with it acting as an acid is slightly harder than it acting as a base...so maybe there are 2 marks for that..but i'm just guessing.
Reply 44
Avatar for Fatima52
Fatima52
Oh yeah- where you got 0.02 conc. at equil: did you square root both sides, or just cancel down the Xs, and cross multiply?
Reply 45
Avatar for Fatima52
Fatima52
Because I remember getting something like: 0.09867x=(another number)
Reply 46
Avatar for rfrd
rfrd
what question are you talking about?
Reply 47
Avatar for jammie08
jammie08
I didn't get 0.02, got 0.01. Don't remember doing any square roots so I must have done it the other way.
Reply 48
Avatar for Fatima52
Fatima52
You had to work out [ ]equil. of one of the reactants, given Kc
Reply 49
Avatar for rfrd
rfrd
if you mean the one under the confusing cooling rapidly one then i also got 0.01 for the concentration.
mucked up the buffer solution one though ..
Reply 50
Avatar for Fatima52
Fatima52
How did you get that answer of 0.01?
Reply 51
Avatar for rfrd
rfrd
i cant remember exactly as in with all the figures, but it involved finding the h+ conc from the pH they gave you and then doing a normal calculation.
Reply 52
Avatar for jammie08
jammie08
yea that's right ( [H+] = antilog - pH ) and then the usual rest
Reply 53
Avatar for Fatima52
Fatima52
One minute- hadn't there been a question which provided the Kc value, and asked us to work out concentration at equil. of one of the reactants/products? I think vol. of 10dm3 was also given? how does pH etc come into this?
Reply 54
Avatar for jammie08
jammie08
yes, there was. I was talking about a different question.
Reply 55
Avatar for rfrd
rfrd
you are thinking of a different question
you are thinking of the question that also included the buffer calculation.
Reply 56
Avatar for Fatima52
Fatima52
Oh ok- so, rfrd, how did you obtain [ ]equil for the question about Kc? presuming that 0.01 was the answer you got for the one about Ka?
Reply 57
Avatar for rfrd
rfrd
i think they gave you kc so i divided kc by the concentrations given for the reactants to get the concentration of the product?
Reply 58
Avatar for Fatima52
Fatima52
by doing that, what was your answer?
Reply 59
Avatar for rfrd
rfrd
i really dont remember!

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