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# Aqa chem 4/ chem 5 june 2016 thread Watch

1. (Original post by Lilly1234567890)
what else apart from potassium nitrate can you use?
KCl, NaCl, Na2SO4

you have to pick one which won't react with either the electrode or the solutions by the the electrode and will allow ions to move across them
2. Guys this is the mark scheme from 2011
3. (Original post by Boundless_x)
I found June 2012 pretty hard
yeah june 12 wasnt great for me either but most of the marks were lost becasue i hadnt learned the colours for metals and the equations (i have now) i got 66 i think 64 was a B. there was this big 12 mark equation/colour questions that tore me a new one
4. (Original post by werdo1997)
Does anyone know the general method of calculation when you have to use the specific heat capacity of water and the mass of something?
You would use the equation
Q= mass of water ×temp change × specific heat capacity ... I believe

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5. (Original post by werdo1997)
Does anyone know the general method of calculation when you have to use the specific heat capacity of water and the mass of something?
I saw a question to work out the temperature change when you dissolve something in water.

They give you the delta H so to get q you multiply delta H by 1000 and the number of moles of the thing you dissolved in water (they give you the mass so you divide it by the reactants Mr to get the moles). Then you rearrange q=mcdeltaT so you divide q by the mass of the water and the specific heat capacity.
6. http://www.thestudentroom.co.uk/atta...9&d=1209931865

Just checking if these are all the colours we need to know and if they are correct?
7. Does anyone no the link between decreasing and increasing temperature on delta s or g ? In one paper it says decreasing temp makes delta g negative but then another says increasing temp delta g becomes negative. I could be way off with these statements. If anyone could simplify this id appreciate it !

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8. (Original post by SirRaza97)
Can I see the past paper where this was???
It was Jan 11 q 6b
9. (Original post by Hopefulmedic15)
Guys this is the mark scheme from 2011
Hmmm I see
Does it have anything on the right hand side like "allow just 1 OH-"
Because tbh I've learned just 1 OH in excess and that's what all the books say so I'm gonna stick with that.
Also I guess as long as there's as increase in OH-'s I'm sure they'll mark it correct as it's still an excess

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10. guys, how do you figure out which the positive/negative electrode is?
11. (Original post by Humza Ali)
guys, how do you figure out which the positive/negative electrode is?
Oxidation always happens at the negative electrode aka the reducing agent.

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12. [QUOTE=Sexybadman;65999065]Does anyone no the link between decreasing and increasing temperature on delta s or g ? In one paper it says decreasing temp makes delta g negative but then another says increasing temp delta g becomes negative. I could be way off with these statements. If anyone could simplify this id appreciate it !

increasing the temp makes T#S bigger therefore it makes #G smaller

#G = #H -T#S
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13. Btw guys when calculating emf is it always the reduced one minus the oxidised one ?

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14. (Original post by GO97)
yeah june 12 wasnt great for me either but most of the marks were lost becasue i hadnt learned the colours for metals and the equations (i have now) i got 66 i think 64 was a B. there was this big 12 mark equation/colour questions that tore me a new one
Now that I think about it... That was probably the main reason why I struggled too since June 2012 is the one I started off with I only got 70 in that paper but the ones I did after that I got into the 80s, thank god. 2015 paper was really good, hope tomorrow will be the same *prays*
15. (Original post by 26december)
Hmmm I see
Does it have anything on the right hand side like "allow just 1 OH-"
Because tbh I've learned just 1 OH in excess and that's what all the books say so I'm gonna stick with that.
Also I guess as long as there's as increase in OH-'s I'm sure they'll mark it correct as it's still an excess

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It allows 4OH- but generally speaking when they say something is in excess it means the reaction goes to completion (i.e. All the waters are substituted out for hydroxide ions)
16. Hi,

A sample of solid chromium(III) hydroxide displays amphoteric character when treatedseparately with dilute hydrochloric acid and with dilute aqueous sodium hydroxide.Write an ionic equation for each of these reactions. Include the formula of eachcomplex ion formed.Describe the changes that you would observe in each reaction

I lost the two marks as it wanted the ionic equations? i really can't do them any one help urgently pleasE??
17. (Original post by Boundless_x)
Now that I think about it... That was probably the main reason why I struggled too since June 2012 is the one I started off with I only got 70 in that paper but the ones I did after that I got into the 80s, thank god. 2015 paper was really good, hope tomorrow will be the same *prays*
aqa eats hopes and prayers for breakfast.
18. (Original post by Humza Ali)
guys, how do you figure out which the positive/negative electrode is?
Positive electrode = cathode = where reduction happens

Negative electrode = anode = where oxidation happens

Btw guys when calculating emf is it always the reduced one minus the oxidised one ?

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Whichever gives you a positive answer, but yes.
19. [QUOTE=Humza Ali;65999155]
Does anyone no the link between decreasing and increasing temperature on delta s or g ? In one paper it says decreasing temp makes delta g negative but then another says increasing temp delta g becomes negative. I could be way off with these statements. If anyone could simplify this id appreciate it !

increasing the temp makes T#S bigger therefore it makes #G smaller

#G = #H -T#S
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This isn't correct.

It all depends on whether delta H and delta S are positive or negative.

If #H is negative and #S is positive then #G is always negative

If #H is positive and #S is negative then #G is always positive

If #H is negative and #S is negative then the reaction is only feasible (#G is less than or equal to 0) at low temperatures

If #H is positive and #S is positive then the reaction is only feasible (#G is less than or equal to 0) at high temperatures

Also as temperature increases molecules gain kinetic energy so they move/vibrate more and so have an increase of disorder hence an increase in entropy
20. Guys if something is insoluble e.g. Mg(OH)2 does it mean that ph will not be affected?

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