AQA Chemistry New AS Unofficial Mark Scheme

What did people get for the Mr of M in MHCO3?

for ful redox equation you just combine the two half equations and eliminate the electrons so
2Cl+2CLO-+4H ---> 2CL2 + 2H2O

does anyone have any good notes, links or know any videos to help me learn the practicals for paper 2?

Hey, I was wondering if you remember how many marks was that Barium sulphate question was? Thanks!

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How many marks was it for each of the half equations and the full redox equation! Was it 1 mark each?

must be ClF3 as all the other have cancelling dipoles.

The dipoles on that cancel aswell?
There is no net positive or negative region on that molecule.
Im not sure for that Q i put BF3

i got 149.1 but for the question before I used 3 of the titre values to find the moles.
Apparently you were suppose to use only 2 values which were 0.1 cm^3 of each other

Find mean and mol HCl in 25cm^3 [3]
Find Mr of MHCO3 [3]
How could you reduce percentage uncertainty? [2?]

I think that was it - maybe another part. I am not sure.
6 Maker was how to make a standard solution, which may have been part of it.

Thank you!

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The gas left over was 30 , you didnt take into account what was in excess and in limited. Dont post answers if they're wrong.

Do you remember how you found the Mr of MHCO3? I remember getting an answer that didn't make sense ://

Thanks.

For the overall equation can you divide it all by 2?
Also predicted raw marks for full ums?

I used the 3 titre values, although I am pretty sure you are only supposed to use the 2 within 0.1cm^3, to find mean HCl reacted in 25cm^3.

Use this mean and the concentration of HCl to find how much HCl reacted. It is a 1:1 ratio, but we need how much in 250cm^3 so multiply by ten.

That is how many moles of MHCO3 reacted. You have mass and moles, so Mr = Mass/Moles, to get an answer around 149 for using 3 titre values; not sure what you get if you used 2 titre values, but it won't differ too much.

Marks are probably for:
i)
Correct method of finding mean,
Correct mean,
Correct moles. [3]

ii)
Correct MHCO3 moles in 250cm^3 {ECF, likely},
Use of Mr = Mass/Moles,
Correct Mr {ECF likely} [3]

Hope this helped.

I got 149.1 also , not sure what you mean about the 3 values they were all different by the same amount so you couldn't rule one out ? Any how they can only penalise you for that mistake once so at worse thats a 1 mark loss