AQA A level Chemistry Paper 1 5th June 2018 Unofficial Markscheme Watch

Bulletzone
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Unofficial Chemistry AQA Paper 1 Mark scheme:


Thermodynamics Question
- lattice dissociation: -3888
- entropy change: +181
- dG: -1063 (to 3 SF); increasing the temperature caused dG to decrease because dS is positive so "-TdS" is negative

- 0.0217
- BaCl2 in excess; 10cm3 of Na2SO4 required
- The least soluble Hydroxide is Mg(OH)2


ALUMINIUM QUESTION:
a) AlCl3 + 6 H2O --> [Al(H2O)6]3+ + 3 Cl-
b) with sodium carbonate a white precipitate forms and there is effervescence:
2[Al(H2O)6]3+ + 3 CO32- --> 2 Al(H2O)3(OH)3 + 3 CO2 + 3 H2O
c) initially a white precipitate would form:
[Al(H2O)6]3+ + 3 OH- --> Al(H2O)3(OH)3 + 3 H2O
the white precipitate would re-dissolve when the OH- is in excess:
EITHER Al(H2O)3(OH)3 + OH- --> [Al(OH)4]- + H2O OR Al(H2O)3(OH)3 + 3 OH- --> [Al(OH)6]3- + 3 H2O (both accepatble)

Catalysis:
Platinum
-Reactants adzorb, reaction takes place, desorb.
-Lowers Ea held by intermolecular forces so higher probability of successful collisions with correct orientation (don't think that bits relevant I was just rambling) The mechanism of how it lowers Ea is a bit fringey on the spec, weakens bonds in reactant so less energy required for reaction.
Contact Process
-V2O5 + SO2 => SO3 + V2O4
-V2O4 + 1/2O2 => V2O5


6 MARK QUESTION:
- NaBr and NaI are both giant ionic lattices with strong electrostatic attractions between positive and negative ions which require a lot of energy to be overcome. However, the I- ion has a larger radius than Br- and therefore a smaller charge density. Therefore the ionic bonding in NaI is weaker than in NaBr, requiring less energy to be overcome.
- Na is a metal with metallic bonding between Na+ ions and a sea of delocalised electrons. However this is not as strong as the ionic bonding in NaBr/NaI because metallic Na does not exist in a giant lattice.

Ionisation Energy
Comparison of second IE of K and Ca
-K has highest second IE
-Electron removed from 3p rather than 4s
-So less shielding, greater attraction to nucleus, requires more energy to overcome.
Highest first IE in s-block:
-Beryllium as it has joint least shielding with Lithium
-But an extra proton so stronger attraction to the nucleus, requires more energy to overcome


ELECTROCHEMICAL CELLS QUESTION:
a) Ions in the salt bridge are free to move, carrying a charge and completing the electrical circuit.
b) V = 0.34 - EMF
c) Because the concentration of Cu2+ ions in the LHS cell is lower than 1 mol/dm3 which is what's required for the standard electrode potential.
d) The concentration of Cu2+ ions would increase over time
e) EITHER the concentrations of Cu2+ become equal OR all the metallic copper on the LHS runs out (both acceptable)

KP QUESTION:
- partial pressures were 7.5, 22.5, 120.
- Expression for Kp = ( p.N2 * p3.H2 ) / ( p2.NH3 )
- units for Kp = kPa-2 (2.99x10^-3)
- since the reaction is exothermic, increasing the temperature moves the position of the equilibrium to the left, reducing the partial pressure of NH3 and thereby decreasing Kp.

Isomerism and VSEPR Shapes:
- isomerism is cis-trans (or e/z); the other isomer had the two Cl ligands opposite each other

- bond angle was 104.5 degrees. The central N had 6 of its own electrons (5, +1 due to the overall negative charge).
Two electrons used in bonding to H atoms so two lone pairs. Shape is tetrahedral but lone pairs repel more than bonding pairs, reducing the bond angle from 109.5 by about 5 degrees (2.5 per lone pair).



Last question
x = 1
Don't even ask how I did the last question, it just worked.

Contributors (Make sure to rep them when you see them):TruthfulHoax 67823 Psychology109 Alof209 Tommy59375
Hajra15
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Evil Homer
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Bulletzone


Hey, can I ask what exam this is supposed to be for?
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Bulletzone
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Enthalpy of lattice dissociation was -4136
Entropy change = +180 or 181
Delta G = -1063
Percentage of 88Sr = 80%
Length of TUBE = 1.54m
pH = 13.09
ph buffer = 4.28
Electrode potential = 0.18V


will update
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medic32344
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Lattic dissociation was -3888
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Bulletzone
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(Original post by Evil Homer)
Bulletzone


Hey, can I ask what exam this is supposed to be for?
AQA A2 CHEMISTRY A LEVEL


mods can u edit my title plz and move to correct section
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Bulletzone
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Concentration of something was 0.0127

267cm^3

10cm^3 required to completely dissociate
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Bulletzone
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x = 1
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guy1729
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Unofficial markscheme.

Post you're answers you remember ?

What was the value of X at the end ?
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Psychology109
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(Original post by Bulletzone)
Enthalpy of lattice dissociation was -4136
Entropy change = +180 or 181
Delta G = -1063
Percentage of 88Sr = 80%
Length of TUBE = 1.54m
pH = 13.09
ph buffer = 4.28
Electrode potential = 0.18V


will update
Wasn't lattice of dissociation something like -3888 Kj mol-1 since they didn't give you enthalpy of atomisation for Oxygen but rather the bond dissociation enthalpy so you had to divide by 2???
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ChocoMocoHD
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I got x = 1.
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If you remember any questions & answers, please comment below

Lattice formation: -3888 kJ mol (3marks)
Kp: 2.99x10-3
Entropy: 181
Gibbs free: -1063
TOF distance: 1.54m (5 marks)
PH: 13.1
Ph: 4.28
Electrode potential: +0.18 (1 mark)
Ideal gas volume: 133cm
Concentration: 0.0218 (1 mark)
Type of isomerism: optical
Bond angle: 104.5 (3 marks)
Transition metals: complex ion Al3+
Al3+ with Co32-: white precipitate & effecversence (2 marks)
Back titration: 1 (7 marks)
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AlkynesOfTruble
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I got abundance as 10% how did you get 80???
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Yokai2
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what is chemitry. i forgot 1000% of all paper 1 for 100% of my subjects. I remember period table has hydrogen first thats it
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Bulletzone
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(Original post by Psychology109)
Wasn't lattice of dissociation something like -3888 Kj mol-1 since they didn't give you enthalpy of atomisation for Oxygen but rather the bond dissociation enthalpy so you had to divide by 2???
mb yeah it's-3888
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Bulletzone
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(Original post by AlkynesOfTruble)
I got abundance as 10% how did you get 80???
I got 2 As 10% and 1 as 80%
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guy1729
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(Original post by guy1729)
Unofficial markscheme.

Post you're answers you remember ?

What was the value of X at the end ?
Feel free to fill in this survey:

https://goo.gl/forms/XUk9T74oxmFOCtuj1

Results are here:

https://docs.google.com/spreadsheets...WNPyGYY5Iby_M/
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AlkynesOfTruble
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(Original post by Bulletzone)
I got 2 As 10% and 1 as 80%
oh f*ck I forgot to take away from 100!!!!!!!!!!!!!!! got the correct value for x but forgot to do 100 - 2x = 80!!!!!!!!! how many marks do you reckon???
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JJarvisCocker
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(Original post by AlkynesOfTruble)
I got abundance as 10% how did you get 80???
X =10
So you had to do 100-2 x =80
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AlkynesOfTruble
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(Original post by JJarvisCocker)
X =10
So you had to do 100-2 x =80
How many marks would I get if I forgot to do the subtraction???
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What was x for the last question?
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X

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