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# Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread watch

1. Mole ratio doubt -

C : H : O
1.3 : 3 : 1

should I round up 1.3 to 2 or 1?
2. (Original post by ihaspotato)
Mole ratio doubt -

C : H : O
1.3 : 3 : 1

should I round up 1.3 to 2 or 1?
Multiply everything by 3?
To give r C4H9O3 I mean
3. (Original post by C0balt)
Multiply everything by 3?
To give r C4H9O3 I mean
I took 1.3 as an example.. but there was a paper where the ratios were

1.75 : 3 :1
(x4)
giving C7H12O4

but I wanted to know if it was 1.3 - should I round it up to 1 or 2?
4. (Original post by _H_V)
When calculating pH of buffer do you use the moles of the weak acid and its salt or do you use the concentration of each in the equation?
I just did a couple of buffer questions and realised I was forgetting to change the moles of the acid and salt back into concentration to put into the equation but the answer was still correct.
Anyone ?
5. (Original post by ihaspotato)
I took 1.3 as an example.. but there was a paper where the ratios were

1.75 : 3 :1
(x4)
giving C7H12O4

but I wanted to know if it was 1.3 - should I round it up to 1 or 2?
Do you mean round it up to 1.0 or 2.0? I don't think you should do that because 0.3 is quite significant as opposed to 0.08 or 0.91 or something!
I think it depends how high or low the 0.3 is. I always go with gut feeling lol
6. (Original post by _H_V)
Anyone ?
Concentration
7. Data booklet

CH ppm 1.8-3.0 how? what does it fall under?
8. (Original post by _H_V)
Anyone ?
Perhaps the answers were still correct because the volumes cancelled?
9. (Original post by ihaspotato)
Data booklet

CH ppm 1.8-3.0 how? what does it fall under?
Can you screenshot the question? We need the context of the CH group
10. (Original post by ihaspotato)
Data booklet

CH ppm 1.8-3.0 how? what does it fall under?
It's the H-c-c=o environment I believe if you look at the data booklet
This is June 15 isn't it I did it this morning
11. (Original post by Funky_Giraffe)
Can you screenshot the question? We need the context of the CH group
12. (Original post by ihaspotato)
It's the because it's the H in the H-C-C=O, which shows up at 1.8-3.0ppm
13. (Original post by Funky_Giraffe)
It's the because it's the H in the H-C-C=O, which shows up at 1.8-3.0ppm
Ahh makes sense. Thanks!
14. (Original post by _H_V)
Anyone ?
think of it this way, to work out conc for A- and HA u had to divide moles by volume; as the amount of volume in the solution is the same you divide both molar amounts by the same number(v), so its: A-/V divided by HA/V. As the v's cancel you are just left with the molar amounts. (A- divided by HA).

You can skip converting to concentration essentially but ka definition is using concentration values not molar amounts
15. I think you tend to get method mark by calculating the concentration even if you don't really have to. That is often the case with Kp calculations etc, so i do every step just in case I mess up some place
16. Why a solution of CH3COONa is a stronger acid than NH3 (wouldn't the ammonia dissociate to give NH4+ ?
Attached Images

17. (Original post by PlayerBB)
Why a solution of CH3COONa is a stronger acid than NH3 (wouldn't the ammonia dissociate to give NH4+ ?
Yes but that also gives OH- ions in solution. NH3 is not an acid.
18. (Original post by Funky_Giraffe)
Totally agree with this. Although being the last main-sit exam in this series, the potential is there for them to pull out all the stops and make this unit 4 a hard one...
was searching for ways for them to 360noscope us to re-sit the exam next year and then I find this - May 2016 C1 news.
19. (Original post by PlayerBB)
Why a solution of CH3COONa is a stronger acid than NH3 (wouldn't the ammonia dissociate to give NH4+ ?
20. (Original post by C0balt)
B (3,2,1)

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