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    (Original post by 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??
    Yep you're wrong. You need to use the enthalpy of hydration for the bromide ion too so it's hyd(K+) + lat diss. + hyd(Br-)
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    (Original post by fabo)
    i did exactly the same
    i forgot to turn to the back page
    Nooo I did the back page LOL but did was have to write out that complex! Cos I don't remember doing that
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    (Original post by erniiee)
    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 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 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..
    Have B'ham specified chemistry as the A*?

    I missed 1/2 out fo five on the last question, 3 marks for not getting the cobalt catalyst equations, 4 marks for the q=mcDT question (wrote m=qcDT -_- ) and the one about the ionic model- I didnt put no covalent character i put even charge density. So that's 10 off the bat and maybe another 10 more due to poor explanations etc. Hoping not much lower than that though
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    (Original post by ImaNeek)
    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"
    For question 4e it was the reaction of phosphorous oxide with NaOH not MgO .
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    For the qmc delta t question, I worked ourt moles of kcl and worked out the energy, and stated the equation, but didnt convert to joules would I get 3 marks perhaps?
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    (Original post by khalidpatel)
    Hey what did u get for the last question?


    Posted from TSR Mobile
    i got 1:3 in favour of chloride ions as used the data to find out both moles and got 1:2.89999 which i made 1:2.9 so assumed a 1:3 ratio and so i think it was [cocl3(nh3)]- apparantly the charge isnt meant to be there but the ratio was 3-1 so had to be cl3nh3 and cl3 has a single negative charge nh3 is neutral and i was unsure as to why the ratio was different or whatever thelast bit asked, many people in my school got 3:1 what did u get?
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    (Original post by AspiringGenius)
    It was the one on the back of the paper, you had to calculate the mole ratio of chlorine to Cobalt (which was threene), 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?
    i put cocl3nh3 but i put a negative charge because technically that would be the charge but then that makes in an ion so i'm unsure, but if cocl2nh3 is neutral cocl3nh3 is -1? any thoughts mate?
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    Ok. Looking at that mark scheme and all of the previous year's grade boundaries, I have got a D when I was aiming for an A. Completely messed up that exam. So angry with myself. How was I supposed to know the unit of frequency. That's not general knowledge and Ive never been taught that. Grrrrrrrr
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    You know it said excess dilute ammonia, did this mean it didn't go all the way. I put it goes all the way but apparently that's when you have excess concentrated. Snotty questions putting in excess when it was dilute you had to focus on. AHHHHHHHH. I put colourless -> colourless on both ag and al.
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    no no no, the question 1 e said would you expect the ionic model to greater equal or less than the actual enthalpy value, if the agcl has covalent character then this means its more exothermic as covalent bonds strengthen the lattice, so the ionic model would be less than the actual model
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    (Original post by zbubbly)
    no no no, the question 1 e said would you expect the ionic model to greater equal or less than the actual enthalpy value, if the agcl has covalent character then this means its more exothermic as covalent bonds strengthen the lattice, so the ionic model would be less than the actual model
    Well no because its asking about lattice dissociation, which is endothermic, so would increase, and no because the additional strength of covalent character with the ionic lattice means there needs to be more energy to overcome these forces, the only exception of this rule however, for a very complicated reason is Al2O3
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    (Original post by SexyAndIKnowIt.)
    You know it said excess dilute ammonia, did this mean it didn't go all the way. I put it goes all the way but apparently that's when you have excess concentrated. Snotty questions putting in excess when it was dilute you had to focus on. AHHHHHHHH. I put colourless -> colourless on both ag and al.
    That's what I put too! We've always learnt it has NH3 and Excess NH3 so I just used it how I was taught. Even though it is dilute, surely an excess would mean you still had enough NH3 for the reaction to go all the way.
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    (Original post by SexyAndIKnowIt.)
    Ok. Looking at that mark scheme and all of the previous year's grade boundaries, I have got a D when I was aiming for an A. Completely messed up that exam. So angry with myself. How was I supposed to know the unit of frequency. That's not general knowledge and Ive never been taught that. Grrrrrrrr
    You're supposed to deduce the unit of frequency the same way you deduce the units on the equilibrium constant in Unit 4. v = E/h, and E is in J, h was in Js, so you have

    units = J/Js = 1/s = s^-1. So the unit of frequency is just 'per second'.
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    hi what did everyone get for the q=mcdt question, i got 503k

    also on the last question i got a 2:1 ratio, how did people get 3:1?
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    (Original post by Milkandcookies5)
    You're supposed to deduce the unit of frequency the same way you deduce the units on the equilibrium constant in Unit 4. v = E/h, and E is in J, h was in Js, so you have

    units = J/Js = 1/s = s^-1. So the unit of frequency is just 'per second'.
    They will probably allow Htz as well
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    (Original post by smithy55)
    hi what did everyone get for the q=mcdt question, i got 503k

    also on the last question i got a 2:1 ratio, how did people get 3:1?
    507K is a really big temperature change for something dissolving in water. I got like 7 something
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    Is there a unofficial markscheme anywhere on this thread??

    Posted from TSR Mobile
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    (Original post by Hart1995)
    Is there a unofficial markscheme anywhere on this thread??

    Posted from TSR Mobile
    "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"

    I did not write this
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    yeah i thought 503 was a bit big but i didn't know what to use for q
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    (Original post by SexyAndIKnowIt.)
    Ok. Looking at that mark scheme and all of the previous year's grade boundaries, I have got a D when I was aiming for an A. Completely messed up that exam. So angry with myself. How was I supposed to know the unit of frequency. That's not general knowledge and Ive never been taught that. Grrrrrrrr
    Didn't you use the AQA official book for chemistry? Moreover it said you need to know and understand ▲E=hV
 
 
 
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