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# 2017 AQA A-Level Chemistry 7405/1 Unofficial Markscheme watch

1. Yoo listen people, i'd post this on the thread but it would get lost in the replies, so here's my answers for today's paper.

I don't remember the units, but if u got same answers thumbs up this post so i know how i did!

-869
1.05
7.27
12.95
8.14*10^-26
9.612*10^-7 seconds [TOF]
-238 KJ Mol-1
9.41*10-7 kPa^-2 [KP]
56.6%
[Fe(C2O4)3]^3-
Shape = Octahedral
Isomerism = Optical Isomerism
Bond Angle = 90 degrees
The Copper colorimeter one = In the complex, copper has a full 3d sub-shell, electrons can't absorb wavelength of visible light and get excited (get promoted from ground state), therefore no light transmitted.
2. pH was 4.50?
3. ****, I forgot to convert my entropy value to kJ
4. (Original post by Wbauxhswsnx)
pH was 4.50?
Yes it is
5. ph for the buffer solution 6 marks was 4.50 bro
6. Your 4.84 buffer isn't right I think but the rest look correct
7. (Original post by wannabe_lawyer)
****, I forgot to convert my entropy value to kJ
same but who gives a **** its like 1 mark off
8. Method for the 8 Marker

Titration 1
• Work out moles of Manganate ions
• Multiply by 5/2 to get number of moles of C2O42- ions

Titration 2
• Work out moles of OH-
• Divide by 2 to get number of H2C2O4 moles

Calculation
• Subtract number of H2C2O4 moles from number of moles of C2O42- ions
• Multiply by 10 (as these moles are only in 25cm3 but total solution was 250cm3)
• Multiply moles by Mr of the sodium ethanoate to get it's mass
• Divide this mass by the total mass (1.9g)
• Multiply by 100

Thus 56.6%
9. (Original post by DarkEnergy)
Method for the 8 Marker

Titration 1
• Work out moles of Manganate ions
• Multiply by 5/2 to get number of moles of C2O42- ions

Titration 2
• Work out moles of OH-
• Divide by 2 to get number of H2C2O4 moles

Calculation
• Subtract number of H2C2O4 moles from number of moles of C2O42- ions
• Multiply by 10 (as these moles are only in 25cm3 but total solution was 250cm3)
• Multiply moles by Mr of the sodium ethanoate to get it's mass
• Divide this mass by the total mass (1.9g)
• Multiply by 100

Thus 56.6%
YEET
10. What was up with Question 10.3?
11. Btw just adding it out there, 0.62 V
12. PRSOM @ so many people
13. (Original post by EvilScientist)
What was up with Question 10.3?
The reduction in the table was wrong. It said

Fe3++ e---> Fe3+

So instead of being logical and telling us to correct the second Fe3+ to Fe2+ they basically stopped us from getting an extra two easy marks
14. How did you get 4.5?

I converted everything to moles
Subtracted moles of added sodium hydroxide away from ha, added sodium hydroxide moles to a-
Worked out h+ then worked out ph

I got 4.78
15. For the ionic equation for the transiton metal did anyone get
h plus + oh- =h20
16. For the 12.95 answer...i got it, but for some reason simpfied it to 13.00?????
17. What was 1.05 the answer to?

Posted from TSR Mobile
18. (Original post by wannabe_lawyer)
****, I forgot to convert my entropy value to kJ
damn i did too, no wonder my value was wack
19. (Original post by Bwile12)
How did you get 4.5?

I converted everything to moles
Subtracted moles of added sodium hydroxide away from ha, added sodium hydroxide moles to a-
Worked out h+ then worked out ph

I got 4.78
I dont think you were supposed to convert into moles...
Just find the concentration of naoh.,,
Add that to the conc of ethanoate... this is the new conc of ethanoate
Then subtract the concentration of naoh from the conc of acid... this is the new conc of acid,,,
Then using ka from previous part
Rearrage to find conc of h+
And then -log it and get 4.5

Thats what i did
20. (Original post by CalmaCalmaC4Away)
What was 1.05 the answer to?

Posted from TSR Mobile
concentration of ethanoic acid

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