Chemistry F215 unofficial mark scheme

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Mule
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#1
Report Thread starter 7 years ago
#1
These are by no means the correct answers, just some of the answer I remember putting, please do not feel disheartened if you don't get similar to me. I could be wrong, or the mark scheme may have more possible answers. You will get ECF for calculation errors

Q 1)
Fill in the blanks (3)
  • K(g) + S (g)
  • K+(g) + S-(g) + e-
  • K+(g) + S2-(g)

Define in words lattice enthalpy (2)
  • Enthalpy change when 1 mole of an ionic compound is formed
From its gaseous ions
Calculate lattice enthalpy (2)
  • -2116 or something


Which has highest m.p.? (3)
  • in order from lowest KI thing, RbCl, NaBr
  • talk about size of ions, difference in ionic radio
  • greater force of attraction = more exothermic lattice enthalpy

Q2
Entropy +/- explain (3)
  • negative, decrease in disorder, held in lattice
  • positive, ions in (aq) gas released
  • negative, fewer moles of gas produces, less disorder etc.

How does feasibility change with temp (2)
  • -TdeltaS is positive, so as T increases -TdeltaS becomes more positive
    -deltaH-TdeltaS becomes greater than 0

Calculate G (2)
+76
Calculate T at which reaction feasible(2)[*] 877.9
Q3
What is the overall order? (1)[*] 5
Why does more than 1 step take place (2)[*]Talk about atoms/ions in r.d.s. and in overall equation, need to add up[*] Negative intermediate needs to be formed[*] unlikely they will all collide at the same time
Draw rate-conc graph (2)[*]Straight line, constant gradient through origin[*] exponential line, increasing gradient
Fill in the table (2)[*] 5.6[*] 600 something
Calculate rate constant and units (2)[*] 6.7 x 10 ^8 [*] dm12mol-4s-1
Calculate initial rate with CH3COOH not HCl (3)
5.33 x 10 ^ -3
You use Ka to find [H+] and then either put back into rate equation or compare to [H+] in HCl and multiply rate by same decrease



Write Kc (1)[*] can't remember
Calculate moles (1)[*] you had to multiply the thing formed by 3 to get moles of other product
calculate Kc and units (3)[*]0.1 something I think, had to divide moles by 4 (volume)[*] mol2dm-6
calculate moles added (1)
I think you had to add double the amount of the product formed to the amount at equilibrium to get the amount added
Table (3)[*] For Increase in temp: greater, greater, greater[*] For increase in pressure: same, smaller, greater[*] For catalyst: same, same, greater
Use of H2 (1)[*] Hydrogen fuel cell/making margarine/haber process



Acid base pairs (2)
CH3COOH + H2O --> CH3COO- + H3O+
acid 1 base 2 base 1 acid 2
Why are there OH- ions? (1)
Not sure, I put because H2O (eqn sign) H+ + OH-
calculate [OH-] (2)[*] Using Kw you get something x10^-11
equation for CaCO3 and CH3COOH(2)
CaCO3 + 2CH3COOH --> (CH3COO)2Ca + H2O + CO2
why is a buffer formed? (1) [*] acid in excess and its salt/conjugate base in high conc
Action of buffer (5)[*] HCOOH --> HCOO- + H+[*] when H+ added reacts with HCOO-[*] p.o.e. shifts to left[*] when OH- added, reacts with H+ to make H2O[*] p.o.e. shifts to right as acid dissociates more, change in pH is minimised
Buffer calculation (5)[*] 11.48g

Why are Sc and Zn not transition elements? (6)
Are in d block as d sub shell highest energy level
needs to form at least one ion with partially filled d subshell
Sc electron config, Sc3+ electron config, d subshell empty
Zn electron config, Zn2+ electron config, d subshell full



How does O2 transported in blood/ligand substitutions (2)
Fe2+ binds to Oxygen
O2 can be released, CO2 replaces in ligand substitution
Kstab for equation (1)
same as Kc basically as there is no H2O anyway
why no O2 carried with CO (2)
Kstab for complex with CO stronger
coordinate bond is stronger
Why is it a bidentate ligand?(2)
Nitrogens each have lone pair of e-
which can donate to central metal ion, forming 2 coordinate bonds for each ligand
Formula of ion (1)
[Cr(NH2CH2CH2NH2)2Cl2]+
Coordination number (1)
6
isomers (3)
One mark for trans isomer
2 marks for cis isomers which are non-superimosable mirror images

Define standard electrode potential(2)[*] e.m.f. of half cell compared with standard hydrogen half cell[*] 1 mol dm3, 298K, 1atm
Write equation for Cu and Au (1)
Cant remember but you had to multiply Au one by 2
add water what happens? (3)[*] concentration of Cu2+ (aq) decreases[*] P.o.e. shifts to left to form more so E becomes more +/ less -[*] difference in E between Cu/Cu2+ and Au/Au+ becomes greater
Why is H2 good as fuel? (1)[*] less pollution/CO2/CO released
How else can it be stored? (1)[*] as a liquid under high pressure
what is the E for Al half cell (1)[*] -2.7 something
Write overall cell reaction (2)
Cant remember but I think mine went overall to just one product


Write overall equation (2)[*] Fe2O3 + OH- + Cl2 --> Fe3+ + Cl- something, I can't remember
Write ionic equation with state symbols (1)[*] Fe3+ (aq) + something ---> something
What is the reducing agent in terms of e- (2)
I- is reducing agent
Each loses 1 electron (gained by reduced species)
% by mass of ppt. (4)
51.8%
Formula of gas, ppt. and equation (3)
O2
Fe(OH)3
Still unsure about equation; this is what I put
2Fe3(thing whatever it was) + 2H+ + 3H2O --> O2 + 2Fe(OH3) + OH-
something like that anyway...
5
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izzaha
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#2
Report 7 years ago
#2
I think you mean f325, thanks anyway
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Astrike
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#3
Report 7 years ago
#3
why did you get -1660?
there was x2 for K
4
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Mule
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#4
Report Thread starter 7 years ago
#4
(Original post by izzaha)
I think you mean f325, thanks anyway
Oops cannot I change it
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Mule
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#5
Report Thread starter 7 years ago
#5
(Original post by Astrike)
why did you get -1660?
there was x2 for K
So sorry what was the value? I can't remember
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gaby_xo
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#6
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#6
There was another Kc question , it asked the original amount added for 1 mark I think

thanks for this!
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xT4Z1N4TRx
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#7
Report 7 years ago
#7
For why H2 is better, can we say better efficiency?
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Lean69
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#8
Report 7 years ago
#8
got 96 what grade will this be
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izzaha
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#9
Report 7 years ago
#9
(Original post by gaby_xo)
There was another Kc question , it asked the original amount added for 1 mark I think

thanks for this!
Yh I think I got 0.1496 or something like that?
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Mule
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#10
Report Thread starter 7 years ago
#10
(Original post by Lean69)
got 96 what grade will this be
It's out of 96, I still have 4 marks missing.
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Ismira
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#11
Report 7 years ago
#11
(Original post by Astrike)
why did you get -1660?
there was x2 for K
I got that and multiplied all by x2

Posted from TSR Mobile
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gaby_xo
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#12
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#12
(Original post by izzaha)
Yh I think I got 0.1496 or something like that?

Same!
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tetra-s
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#13
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#13
Wasn't there a question in which he increased all the concentrations I- IO3- and H+ by x4 and you had to predict the rate
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CallumHall57
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#14
Report 7 years ago
#14
  • The delta G was +76.0kJmol-1
  • T was 877.9/878K
  • the multi step one could have involved using/reforming catalysts in different steps
  • initial rate with CH3COOH was 5.33x10-3 moldm-3s-1
  • Could also have put more efficient than fossil fuels for the hydrogen fuel cells
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carly_muse
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#15
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#15
On the exam it said that ch3cooh was the weak acid, so surely that will dissociate to form ch3cooh2, and oh-? (I think anyway)
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HollyWoolnough
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#16
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#16
Wasnt there one about uses of hydrogen?
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Mule
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#17
Report Thread starter 7 years ago
#17
(Original post by carly_muse)
On the exam it said that ch3cooh was the weak acid, so surely that will dissociate to form ch3cooh2, and oh-? (I think anyway)
I would have thought a weak acid is still more acidic than water.
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edward12
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#18
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#18
weren't the graph rate-time graphs if not then i ****ed up??
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adam_dewji
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#19
Report 7 years ago
#19
(Original post by edward12)
weren't the graph rate-time graphs if not then i ****ed up??
They were initial rate-conc graphs i think
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edward12
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#20
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#20
(Original post by adam_dewji)
They were initial rate-conc graphs i think
**** two easy marks gone
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