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Aqa chem 4/ chem 5 june 2016 thread

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That was a lil sneaky of AQA that they specified Na-P, thankfully I actually managed to read the question for once otherwise would've got it wrong
Reply 2341
Avatar for Qrstuv
Qrstuv
I got 74.3% for purity but if that's incorrect I can't work out where I've gone wrong..
I think it was 26.4cm3 KMnO4 at 0.02moldm-3 which is 5.28x10-4 moles
Then ratio 2:5 is 1.32x10-3 moles of C2O4 in 25cm3 and 0.0132 moles in 250cm3
0.0132 / 3 is 4.4x10-3 then I multiplied by Mr for mass of 2.16g?
Original post by 1010marina
94.4% purity anyone?


Yaaas! :biggrin:

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X = Phosphorus
Y = Sodium
Z = Al2O3
Original post by lahigueraxxx
I got that! It's wrong though unfortunately :frown:
how many do i lose
What was enthalpies of dissociation I think question 3?
What an absolute beautiful paper! only thing I feel like I messed up on was redox alkali half equations and the effect of pressure. Which was five marks altogether, though I may stil have got a few. Talked to A* kid in my class and got the same results as him for most calculations and got 94. Something % for impurity thing. i will be surprised if I don't get an A*. This paper has certainly made up for the horrendous unit 4 paper
I got 94.4% purity and ticked hno3 kms
Does the pressure have an effect on the emf? I said the emf increases eqbrm shift blah blah, but wasn't sure on that
I got something like -197 for enthalpy change and -182? Or something for entropy cant remember 100%
Original post by berries366
I got something like -197 for enthalpy change and -182? Or something for entropy cant remember 100%


Think I got -196 for enthalpy
and -189 for entropy
Hi I have some questions and answers if anyone wants to add to it?

Lattice dissociation of K2O being less endothermic than Na2O:

K+ ions are bigger than Na+ ions
Weaker electrostatic force of attraction between K+ and O2- ions/weaker ionic bonding
Less energy needed to break the ionic lattice

Solubility of MgCl2 decreases
Forward reaction is exothermic
Equilibrium shifts left to oppose increase in temperature

Enthalpy of solution = -155 kJ/mol
Original post by Number Nine
I got 94.4% purity and ticked hno3 kms


I think it was h2so4, that's what I put
Reply 2353
Avatar for Jenza
Jenza
1
What did people get in the percebtage purity question? Anyone get around 50% ish?
Did anyone else pick sulphur for X?
I'm such an idiot 😂😂😭

Still such an easy paper I'm so happy
How many marks would i lose for getting 50% not 94%? I forgot to times c2o4 moles by 3..
Original post by berries366
I got something like -197 for enthalpy change and -182? Or something for entropy cant remember 100%


Original post by thehollowcrown
Think I got -196 for enthalpy
and -189 for entropy


It wanted standard enthalpy change, hence you do it for one mole hence you divide answers by 2 I believe (that's what happened on a previous mark scheme)
(edited 7 years ago)
Original post by cowie
I thought hydrogen oxygen cell was my reversible and hence lie chateliers principle wouldn't have any effect?


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What are you talking about
Original post by thehollowcrown
Think I got -196 for enthalpy
and -189 for entropy


Yeah think thats what i got lol cant remember 😆
Original post by Hannahbram
How many marks would i lose for getting 50% not 94%? I forgot to times c2o4 moles by 3..


You'd still get most of them, normally those questions are around 5 marks but this one was 7 because it had the extra step so maybe you lost like 2?

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