AQA CHEM5 A2 Chemistry - 19th June 2013

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Reply 3220

mulac1

yep

thanks

Reply 3221

alex7892

Grade boundary predictions? Lol why is everyone ignoring my comments x

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Reply 3222

esl_94

Original post by mulac1

no - the 2nd page of question 8 :smile:

Sorry about that my brain is a bit tired and not entirely functioning! its been a busy couple of weeks! :smile:

again just let me know if you need better copies of any pages or if i still have managed to miss some out... always possible with me :wink:

Reply 3223

naeemkhan12

what did ppl get for Phosphorus with soduim hydroxide

Reply 3224

Ren_9

Original post by alex7892

Grade boundary predictions? Lol why is everyone ignoring my comments x

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A* 78
A 69
B 60
C 52
So slightly lower much than Jan 13

Reply 3225

_jamie

The grade boundaries won't change too much. I remember everyone thinking june 12 was horrific last year and they pretty much stayed the same (and tons of people complained to AQA.

ISNT 7a WRONG PPL

Original post by alex7892

Grade boundary predictions? Lol why is everyone ignoring my comments x

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Because nobody knows. And you can't really trust anyone who is not an Aqa examiner.

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Reply 3228

MedicineMann

do you think for question 7 they will accept
[fe(h20)6]2+ + 2NaOH --> Fe(h20)4(OH)2 + 2H20 + 2Na+
etc.
I think you were just supposed to put ionic oh-

Reply 3229

godjohnson

Original post by esl_94

Sorry for the delay - I think these are Questions 6 and 7 :smile:

Again if I have missed any pages just let me know :smile:

I seem to have 18 photos on my phone and have put 17 up here but I can't work out which I have missed!

Cant you just put up the whole paper??

Reply 3230

godjohnson

What's this question with substance Z (Co(NH3)2 cl2) ?? I don't remember it at all

Reply 3231

godjohnson

Original post by naeemkhan12

ISNT 7a WRONG PPL

Yeahh the equation for Fe2+ is completely wrong

Reply 3232

Anshul91

Isnt question 2(b) 26 kj mol???

The enthalpy of hydration for the potassium ion is -322 and the dissociation for potassium bromide is +670, calculate the enthalpy of solution of potassium bromide:

enthalpy of solution = lattice dissociation + sum of hydrations

+26 = +670 + (-322 x 2)

am I wrong??

Reply 3233

Anshul91

Original post by nimbusquaffle

2a) Cl- ion is a smaller ion than Br- so has greater electronegativity. water is polar so contains a ~+ H+ ion. therefore Cl-is more attracted to H2O than Br- so more energy is released when hydration happens
b) 13kJmol-1
c) increase in entropy and 1mole ---> 2moles. more disordered. ΔH<tΔS. therefore ΔG<0 nd feasible.
d) have no idea!

3a)i at 0K all substances are completely ordered. moles are constant with no vibrations. absolute entropy.
ii as temperature increases entropy increases, molecules vibrate more violently becoming more disordered
iii in line with L2
iv phase change causes a sudden increase in entropy. boiling has a greater increase in entropy than melting so L2 is greater than L1.
b)i ΔG=ΔH-TΔS can be rearranged to ΔG=-ΔST + ΔH. ΔS is m (gradient) ΔH is the constant c. ΔG is y and T is x. therefore follows the same equation. ΔS is negative due to negative gradient.
ii as T increases TΔS, because ΔH is constant. as T increases ΔH - TΔS decreases, ΔG decreases.
iii becomes feasible
c)i -44.5 Jk-1mol-1
ii 242 kJmol-1

hopefully help, correction ma be needed! :biggrin:

3 part 3, its unfeasible below 500K as G is positive.

Reply 3234

AspiringGenius

Original post by godjohnson

What's this question with substance Z (Co(NH3)2 cl2) ?? I don't remember it at all

It was the one on the back of the paper, you had to calculate the mole ratio of chlorine to Cobalt (which was three :redface:

ne), deduce the structure [CoCl3(NH3)3] and then say why the mole ratio may eb different in practice (no clue).

Guys do you think they would accept [CoCl3(NH3)] as in all fairness, knowing the coordination number of such a random complex is not on the spec?

Reply 3235

erniiee

Original post by AspiringGenius

I found ti quite hard. I know I messed up the qmcDT equation and some of the cobalt chemistry equalling about 10 marks. Although if grade boundaries are low and I did well enough in Chem4 and the EMPA, An A* is achievable (I hope). :s-smilie:

you?

I thought it was really quite hard too..the calculations were a lot more challenging than those on past papers I think. Especially the very last..I guessed the complex was CoNH34Cl2..lol. But I did get the ratio..I think I've lost all marks on the that delta T equation, I didn't use m :s-smilie:

I got the cobalt question though. I think I've lost at least 5 from earlier parts of the paper due to poor explanations..so I'm thinking at least 10-15, maybe more :frown:

hopefully the GBs will be nice and low though..and I'm in the same position - CHEM4 and my ISA went really well, so hopefully this wont pull my UMS down massively. And I need an A*, not so sure what it will be in now though..

Reply 3236

erniiee

Original post by alex7892

Grade boundary predictions? Lol why is everyone ignoring my comments x

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I'm thinking in the range of 77-79 for an A*, 69-71 for an A etc, most probably on the lower side of those as there was a lot of maths that wasn't straightforward

Original post by godjohnson

What's this question with substance Z (Co(NH3)2 cl2) ?? I don't remember it at all

Was on the back page.. :eek:

Reply 3237

erniiee

Original post by Croydon'Stepper

2a, you don't talk about electro negativity as it's not a covalent bond.

2b I did the correct method, got -7kJmol-1, but I think I ****ed up the actually calculations

Other than that, got the same as you! :biggrin:

Which page is this unofficial mark scheme on?

Reply 3238

fabo

Original post by godjohnson

What's this question with substance Z (Co(NH3)2 cl2) ?? I don't remember it at all

i did exactly the same
i forgot to turn to the back page :frown:

Reply 3239

ImaNeek

Original post by erniiee

Which page is this unofficial mark scheme on?

Here's what someone posted as the unofficial mark scheme but it incomplete and there some errors.

"This is nearly complete unofficial markscheme:

Q1: a) what is the perfect ionic model (1)
Ions are perfect spheres, only electrostatic attraction/no covalent character
b) define 'standard enthalpy of lattice dissociation' (2)
The standard enthalpy change to convert one mole of a solid ionic lattice into its gaseous, constituent ions
c) Give 2 factors that affect the lattice enthalpy of dissociation (2)
Size of the ion/ionic radius
Charge on the ion
d) calculate the lattice enthalpy of dissociation for AgBr (3)
+905 kJ mol-1
e) How would you expect your value to 1d) to differ with that calculated from the PIModel. Explain (2)
greater;
as there is additional covalent character/bonding

tot = 10

4a) What is the bonding in MgO. How could you prove that MgO has this bonding (3)
Ionic
Heat until molten
Conducts electricity/gives a current when being electrolysed
b) Why is SiO2 insoluble in water (3)
large macromolecule
many, strong covalent bonds
lots of energy needed to be supplied to break bonds/ enthalpy of solution is very large
c) What has a higher melting point - SiO2 or P4O10? Explain (3)
P4O10 is a simple covalent molecule
Weak VdWs (and dipole-dipole) IM forces
Less energy needed to be supplied to break VdWs forces
d) Write an equation to show that MgO is basic (2)
MgO + 2HCl => MgCl2 + H2O
e) Write an equation for the reaction of P4O10 with MgO (1)
P4O10 + 6MgO => 2Mg3(PO4)2
tot = 12

5a) why can KCl not be used as a salt bridge (1)
It is not inert/it reacts with the cell reagents/Cl- oxidized to Cl2 by Cu2+
b) why do the electrons flow from right to left (2)
LHS has a higher conc. of Cu2+ / LHS is positive electrode
Equilibrium Cu2+ + 2e- => Cu lies more to right at the left hand electrode (or converse)
c) Why does the current fall to zero after some time (1)
Cu2+ concentration is the same in both half cells
d) calculate the electrode potential (1)
-3.05V
e) Write the equation for the cell when it is being recharged (2)
LiMnO2 => Li + MnO2
f) Give one reason why this cell produces CO2 (1)
CO2 released generating the electricity needed to recharge the cell
tot = 8

6a) calculate the frequency of visible light absorbed and state the units (2)
4.28x10^14 s^-1 or Hz
b) Why does this compound appear blue (2)
d-orbital electrons absorb visible light energy and are promoted/excited to a higher energy level;
we observe the blue colour that is not absorbed;
c) Red/blue complex. What is the deltaE value of a red solution in comparison with a blue one? (2)
larger;
absorbs blue light which is of a higher frequency;
d) State 3 factors that affect the frequency of visible light absorbed (3)
change in…
oxidation state
ligands
coordination number
tot = 9

7) original colours, final observation, equation for each reaction

a) [Fe(H2O)6]2+ and [Fe(H2O)6]3+ with sodium carbonate (5 marks)
[Fe(H2O)6]2+ = pale green solution
observation = green ppt.
[Fe(H2O)6]3+ = violet/yellow/brown solution
observation = brown ppt and effervescence

[Fe(H2O)6]2+ + CO32- => FeCO3 + 3CO2 + 3H2O
2[Fe(H2O)6]3+ + 3CO32- => 2[Fe(OH)3(H2O)3] + 3CO2 + 3H2O

b) [Cu(H2O)6]2+ and [Co(H2O)6]2+ with HCL (4 marks)
[Cu(H2O)6]2+ = pale blue soln.
observation = green/yellow soln.

[Co(H2O)]2+ = pink soln.
observation = blue solution

[Cu(H2O)6]2+ + 4Cl- => [CuCl4]2- + 6H2O
[Co(H2O)6]2+ + 4Cl- => [CoCl4]2- + 6H2O

c) [Cr(H2O)6]3+ and [Fe(H2O)6]2+ with excess OH- (4 marks)

[Cr(H2O)6]3+ = green or ruby soln.
observation = green soln.

[Fe(H2O)6]2+ = pale green soln.
observation = green ppt.

[Cr(H2O)6]3+ + 6OH- => [Cr(OH)6]3- + 6H2O
[Fe(H2O)6] + 2OH- => [Fe(OH)2(H2O)4] + 2H2O

d) [Al(H2O)6]3+ and [Ag(H2O)2]+ with excess NH3 (4 marks)
[Al(H2O)6]3+ = colourless soln.
observation = white precipitate

[Ag(H2O)2]+ = colourless soln.
observation = colourless soln/no visible change

[Al(H2O)6]3+ + 3NH3 => [Al(OH)3(H2O)3] + 3NH4+
[Ag(H2O)2]+ + 2NH3 => [Al(NH3)2]+ + 2H2O

tot = 17

8a) ethanal can be oxidised to ethanoic acid by O2. Explain why Co2+ ions can increase the rate of this oxidation. Write 2 equations showing how Co2+ does this. (4 marks)

provides alternative mechanism/route with a lower Ea;
as has variable oxidation states;

2Co3+ + CH3CHO + H2O -> 2Co2+ + CH3COOH + 2H+
4Co2+ + O2 + 4H+ -> 4Co3+ + 2H2O

or multiples;;

b) [Co(H2O)6] reacts with an excess of ethane-1,2-diamine. Write an equation for this reaction and explain why ethane-1,2-diamine is the more stable complex (3 marks)

more moles of products than reactants
Increase in disorder
Entropy change large and positive

[Co(H2O)6
c) Draw the complex ion. (3 marks)

arrows showing coordinate bonds from N atom to Co;
octahedral arrangement;
2+ charge;

d) Cobalt ratio question (5 marks)
3:1
[Co(NH3)6]3+
don’t know :P

tot = 15
Its not
[Fe(H2O)6]2+ + CO32- => FeCO3 + 3CO2 + 3H2O is wrong its:

[Fe(H2O)6]2+ + CO32- => FeCO3 + 6H2O

Can somebody finish this off"