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Aqa chem 4/ chem 5 june 2016 thread

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dissocation reactions are endothermic so the forward reaction is endo so the solubility increases when the temp increases as it shifts to the right (the endo reaction) because the solid ionic lattice (magnesium chloride) dissociates into its aqueous ions which increases the solubility. so idk how its a decrease haha
What did people say for effect of increasing pressure on emf
For the Mno4- titration quesiton, i put the ratio of mn04 to c204 as 1:5 instead of 2:5, would i still get error carried forward marks?????
Original post by Guls
mno4- and c2o4^2- are negatively charged so repel and the reaction has a high activation energy. 3 points for 3 marks.


Could you also get a mark for saying the collision frequency is very very low ?


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Original post by 12284
I wrote H+ ions not HCl, do I still get the mark?


I put H+ too but I don't think so because H+ isn't a reagent... So annoying :frown:


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What did people put down for the last question about colorimetry?


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Original post by 12284
I wrote H+ ions not HCl, do I still get the mark?


not sure, think you had to specify with the acid
Original post by ravichauhan11
no , eq shifts to the left, so not favoring the dissociation of MgCl2, therefore solubilty decreases. very similar question came up a few years a go


I agree


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Reply 2448
Original post by olivia7001
Oh did no one write it in terms of entropy? I thought solubility increased because I worked it out with the Gibbs free energy

I talked about gibbs free energy too, but said it increased when temperature increases so it becomes less soluble?

Original post by RefusedAccess
The question stated that solubility is defined as the amount of solid ready to dissolve in a solvent ( in this case, water).
Hence as more MgCl2(s) is being produced, solubility increases.

Aqa were sly with this one like Q1A


What?? So solubility increases? I don't understand what you mean...?
What was the equation for the solution of MgCl2? I couldn't remember solution so i put MgCl2(s) ---> Mg2+(aq) + 2Cl-(aq)
Original post by DDan123
What did people put down for the last question about colorimetry?


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Plot a graph of concentrations and absorption rates using known concentrations of KMnO4
Then set up colorimeter and place unknown sample and see what it's absorption rate is
Use the absorption rate on the graph and go across until you find the concentration

Something like that haha


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Original post by Lazarus26
What was the equation for the solution of MgCl2? I couldn't remember solution so i put MgCl2(s) ---> Mg2+(aq) + 2Cl-(aq)


That's fine.
If u right p4o10 rather than jus p is it rong
Original post by olivia7001
Oh did no one write it in terms of entropy? I thought solubility increased because I worked it out with the Gibbs free energy


I did this too. I thought we had to use the values of the previous part but I think we might have misinterpreted it? Idk


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Original post by DDan123
What did people put down for the last question about colorimetry?


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first said about how MnO4- ions are coloured and the rest arent ( just as an intro). make up solutions of known conc. Measure absorption. plot graph of results, then use the absorption for the unknown conc one to work out the concentration ( extrapolation) .
Original post by sockface
If u right p4o10 rather than jus p is it rong


was the second one Na and not Na2O then?
Original post by Guls
mno4- and c2o4^2- are negatively charged so repel and the reaction has a high activation energy. 3 points for 3 marks.


I also added in:
little Mn2+ formed initially, so reaction is uncatalysed
Mn2+ lowers Ea as allows for reactions between positive and negative ions.

*just* for safety :P
was the enthalpy of solution positive or negative
i didnt do 90x2 for atomisation of potassium oh no how many marks was this question for and how many marks will i get if i did not do that ahhh
so whats everyones grade boundary predictions for chem 4 and them 5 then??

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