Chem5 June 2014 Unofficial Mark Scheme

2 properties of si02?? I said acidic behaviour and insoluble in water :?////

The qs about writing the equation of P4O10 was with MgO not Mg(OH)2 so it should have been P4O10 + 6MgO----> 2Mg3(PO4)2

Any ideas on what 80/100 will be?

Anyone else forget to show ALL the bonds on cis platin
Posted from TSR Mobile

It didn't ask for the display formula?

For the phosphorous oxide and magnesium reaction, I did it as if the reactants were h3po4 and MgO, is this wrong?

This sums up our exam :P :
https://www.youtube.com/watch?v=2tjVAjHFDio


Add below and I will edit it all in with question and Marks.

Write the equation for the electron affinity:
1. Cl + e- ----> Cl- (1 mark)

Why Ea (Electron affinity) exothermic: (2 mark)
(Adding electron- requires energy for sticking of e-) - Debated - need people to suggest their idea.
Weak electrostatic attraction - net gain of e- compared to + proton.

Born haber cycle I got : (3 mark)
Ag(S) + 1/2F2 (g)
Ag(g) + 1/2 F2 (g)
Ag+ (g) + 1/2 F2 (g) + e-
Ag+ (g) + F (g) + e-

Didn't do the bond enthalpy ( 2 mark)
Apparently 158 KJ mol-1

Enthalpy of hydration: ( 2 mark)
Enthalpy change when 1 mole of gaseous ions form 1 mol of aq ions (when bound to water)

Why is enthalpy of dissociation experimental and theoretical are different: (2 mark)
Theroetical takes into account fully ionic
Experimental takes into account covalent character as values are different

AgF and AgCl why is AgF got a higher dissocation value: (2 mark)

Fluoride is smaller ion
Stronger Ionic bond - greater electrostatic attraction- requires larger amount of energy to break bond.



Something about why is the value positive or something like that? (2 mark)
Endothermic-break bonds
Between H delta+ of water and Cl- ion.

Enthalpy of solution: (3 marks)
Got something like -364 KJmol-1

T=2333k (4 marks)
temp is significant because water boils at 373k (ish), so the reaction cannot happen (u can't dissolve something in steam)

Can't remember what I got but I did: I think it was -20.1 ( 3marks)
Delta H-Delta G / T
Temp 25+273=298K
Delta G = -17
Delta H - Can't remember value, possibly


The Mg with water I got wrong: (3 mark)
But the correct answer is MgO
H2
Mg + H20 -----> MgO + H2

Difference between Na and Mg in terms of bonding: (2 mark)
Mg ion-smaller radius/smaller ion
Mg ion 2+ charge and Na +1 charge
Therefore Mg has stronger metallic bonding.

P (V) Oxide question: (3 mark)

P4O10
Covalent bond between O and P with in the molecule
Molecules held by van der waals due to electrons

SiO2 (4 mark)
structure Macromolecule(1)
bonding Covalent(1)
and two properties of sio22)
-Insoluble
-High melting point (compared to simple covalent molecules)

SO3^2- + H20 ----> HSO3^- + OH- (1 mark)

P4O10 + 6MgO----> 2Mg3(PO4)2 (1 mark)

Hydrogen electrode and Fe2+ / Fe: (2 marks)

Pt|H2(g)|H+(ag)||Fe2+(aq)|Fe(s)

What's an Reducing agent: (1 mark)
Electron donor

Weakest reducing agent from column and why (2 mark)
Cl2
And which atom was reduced in HOCl (the tick box question) (2 mark)
Cl Oxygen state goes from +1 ---> O From HOCl to HCl

Hearing aid cell:

(1 mark)
EMF = 1.60 V / 1.65V
Rhs-Lhs

(2 marks)
A- steel lid:
Reduction occurs at the anode

(2 marks)
2H+ + 2e- + O2 ----> H2O
H2 -----> 2H+ + 2e-

Overall equation for H2O2 and ZnO (2 marks)
2Zn + 202---> 2Zno2

Why Fuel cell is better than internal combustion engine (2 marks)

Hazard of using fuel cells (1 mark)
H2 is flammable could lead to explosion


Cis Platin: (3 mark)
90 degrees
Was a square planar with 2 NH3 at top and 2 Cl at bottom
No charge

(1 mark)
[Pt(NH3)2(Cl)2] + H20 -----> [Pt(NH3)2 (H2O) (Cl)]^+ + Cl-

(1 mark)
Administrate a smaller dose reduce toxic effects

(5 Marks): Reaction between 2 aminoethane with [Co(H2O)6]2+

3NH2CH2CH2NH2 + [Co(H2O)6]2+ ------> 6H2O + [Co(NH2CH2CH2NH2)3]^2+

4:7 molar ratio
Entropy increase
TDeltaS> Delta H

Delta S = +Ve
Therefore Delta G<O
Therefore reaction is feasible.

12 marks in total for the following:
1) NH3
Cu(H20)4(OH)2
Equation to form it

2) NH3 in excess
[Cu(NH3)4(H2O)2]^2+

3) Na2CO3
CuCO3

4) HCl
[Cu(Cl)4]^2-


6 marker X^2+ and X^3+ one:
Couldn't answer the first part because I don't how they can have the same electron config
they had the same electron arrangement (and the same oxidation states) but one had a Cl- ligand (oxidation state -1) so overall it had charge +2 (3-1 = 2), tho other only had water (oxidation state 0) and 3±0 = 3 so overall charge 3

Different d - electrons in different D sub shells.
Visible light absorbed, excites electron is different - different Delta E values
Therefore different wavelength of lights are absorbed.

(4 marks)
Overall: SO2+1/2O2 ----> SO3

SO2 + V2O5 -----> SO3 + V2O4
V2O4 + 1/2O2 ----> V2O5

V2O5 provides alternative mechanism with lower Ea. It's a heterogeneous catalyst and is not used up or changed in the reaction.


(5 marks)
5.34g for redox titration

(2 marks)
Last question: Why calculated value is higher than actual. I put impurity X can reduce Cr2O72- therefore more dichromate is needed giving a higher amount of Fe2+ than there actually was.

the total marks add up to 89 ur missing 11 marks worth of questions

the total marks add up to 89 ur missing 11 marks worth of questions

For reagents can you just say Cl- instead of HCl and CO32- rather than Na2CO3??

I probably lost around 35 marks lol.

Posted from TSR Mobile

This sums up our exam :P :
https://www.youtube.com/watch?v=2tjVAjHFDio


Add below and I will edit it all in with question and Marks.

Write the equation for the electron affinity:
1. Cl + e- ----> Cl- (1 mark)

Why Ea (Electron affinity) exothermic: (2 mark)
(Adding electron- requires energy for sticking of e-) - Debated - need people to suggest their idea.
Weak electrostatic attraction - net gain of e- compared to + proton.

Born haber cycle I got : (3 mark)
Ag(S) + 1/2F2 (g)
Ag(g) + 1/2 F2 (g)
Ag+ (g) + 1/2 F2 (g) + e-
Ag+ (g) + F (g) + e-

Didn't do the bond enthalpy ( 2 mark)
Apparently 158 KJ mol-1

Enthalpy of hydration: ( 2 mark)
Enthalpy change when 1 mole of gaseous ions form 1 mol of aq ions (when bound to water)

Why is enthalpy of dissociation experimental and theoretical are different: (2 mark)
Theroetical takes into account fully ionic
Experimental takes into account covalent character as values are different

AgF and AgCl why is AgF got a higher dissocation value: (2 mark)

Fluoride is smaller ion
Stronger Ionic bond - greater electrostatic attraction- requires larger amount of energy to break bond.



Something about why is the value positive or something like that? (2 mark)
Endothermic-break bonds
Between H delta+ of water and Cl- ion.

Enthalpy of solution: (3 marks)
Got something like -364 KJmol-1

T=2333k (4 marks)
temp is significant because water boils at 373k (ish), so the reaction cannot happen (u can't dissolve something in steam)

Can't remember what I got but I did: I think it was -20.1 ( 3marks)
Delta H-Delta G / T
Temp 25+273=298K
Delta G = -17
Delta H - Can't remember value, possibly


The Mg with water I got wrong: (3 mark)
But the correct answer is MgO
H2
Mg + H20 -----> MgO + H2

Difference between Na and Mg in terms of bonding: (2 mark)
Mg ion-smaller radius/smaller ion
Mg ion 2+ charge and Na +1 charge
Therefore Mg has stronger metallic bonding.

P (V) Oxide question: (3 mark)

P4O10
Covalent bond between O and P with in the molecule
Molecules held by van der waals due to electrons

SiO2 (4 mark)
structure Macromolecule(1)
bonding Covalent(1)
and two properties of sio22)
-Insoluble
-High melting point (compared to simple covalent molecules)

SO3^2- + H20 ----> HSO3^- + OH- (1 mark)

P4O10 + 6MgO----> 2Mg3(PO4)2 (1 mark)

Hydrogen electrode and Fe2+ / Fe: (2 marks)

Pt|H2(g)|H+(ag)||Fe2+(aq)|Fe(s)

What's an Reducing agent: (1 mark)
Electron donor

Weakest reducing agent from column and why (2 mark)
Cl2
And which atom was reduced in HOCl (the tick box question) (2 mark)
Cl Oxygen state goes from +1 ---> O From HOCl to HCl

Hearing aid cell:

(1 mark)
EMF = 1.60 V / 1.65V
Rhs-Lhs

(2 marks)
A- steel lid:
Reduction occurs at the anode

(2 marks)
2H+ + 2e- + O2 ----> H2O
H2 -----> 2H+ + 2e-

Overall equation for H2O2 and ZnO (2 marks)
2Zn + 202---> 2Zno2

Why Fuel cell is better than internal combustion engine (2 marks)

Hazard of using fuel cells (1 mark)
H2 is flammable could lead to explosion


Cis Platin: (3 mark)
90 degrees
Was a square planar with 2 NH3 at top and 2 Cl at bottom
No charge

(1 mark)
[Pt(NH3)2(Cl)2] + H20 -----> [Pt(NH3)2 (H2O) (Cl)]^+ + Cl-

(1 mark)
Administrate a smaller dose reduce toxic effects

(5 Marks): Reaction between 2 aminoethane with [Co(H2O)6]2+

3NH2CH2CH2NH2 + [Co(H2O)6]2+ ------> 6H2O + [Co(NH2CH2CH2NH2)3]^2+

4:7 molar ratio
Entropy increase
TDeltaS> Delta H

Delta S = +Ve
Therefore Delta G<O
Therefore reaction is feasible.

12 marks in total for the following:
1) NH3
Cu(H20)4(OH)2
Equation to form it

2) NH3 in excess
[Cu(NH3)4(H2O)2]^2+

3) Na2CO3
CuCO3

4) HCl
[Cu(Cl)4]^2-


6 marker X^2+ and X^3+ one:
Couldn't answer the first part because I don't how they can have the same electron config
they had the same electron arrangement (and the same oxidation states) but one had a Cl- ligand (oxidation state -1) so overall it had charge +2 (3-1 = 2), tho other only had water (oxidation state 0) and 3±0 = 3 so overall charge 3

Different d - electrons in different D sub shells.
Visible light absorbed, excites electron is different - different Delta E values
Therefore different wavelength of lights are absorbed.

(4 marks)
Overall: SO2+1/2O2 ----> SO3

SO2 + V2O5 -----> SO3 + V2O4
V2O4 + 1/2O2 ----> V2O5

V2O5 provides alternative mechanism with lower Ea. It's a heterogeneous catalyst and is not used up or changed in the reaction.


(5 marks)
5.34g for redox titration

(2 marks)
Last question: Why calculated value is higher than actual. I put impurity X can reduce Cr2O72- therefore more dichromate is needed giving a higher amount of Fe2+ than there actually was.

Oh noooooo, I thought the born haber cycle was for AgF !!!!! Damn