F321 January 13th 2011: OCR Chemistry A Exam

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I got 2 for x as well. I think I missed out on a mark on the electronegativity question as my definition was "The ability of an atom to draw in surrounding electrons" where I think I needed to specify it was a covalent bond.

The paper its self was okay content-wise, but the questions themselves were horrible, so many longer answer questions. The halogen/halide displacement took ages, by the end all I wrote about reactivity was "Less reactive down group, greater van der waals forces" and "cyclohexane purple at top", whether these answer will get me any marks as it wasn't in prose I've no idea.

Very very tight on time though, waaay too much to write, think everyone struggled on that more than the content itself.

Reply 21

ChrisHeaton

Original post by fredmc

yeh lots of people didn't finish I think

Reply 22

sofiakousar

Original post by CeeTay

I got x as 2 because it was a 1:2 ratio, but I don't know :/

i got x=2 aswell. maybe its right then

Reply 23

sofiakousar

for the 2nd to last question about ocidation and reduction. between reaction
F2 + H2O= 2HF +1/2O2 what did people get for what was reduced and what was oxidised. i got F was from 0 to -2 and O2 was oxidised from -2 to-1 .
o ye and how did ppl balance it. im not sure if i got this right or not.

Reply 24

sofiakousar

the last question what did ppl get for the formula. i got BeF3 is that right.

Reply 25

sofiakousar

the question about what the shape of 5s orbital was. was the answer a sphere.

Reply 26

sofiakousar

what was the answer for y pure barium would produce less H2. i was totally lost there so i guessed it was produce more of the metal hydroxide.

Reply 27

sofiakousar

can nyone remember what any of the mole/vol/conc question were. if so can u plz tell me.

Reply 28

shaws010

Original post by sofiakousar

what was the answer for y pure barium would produce less H2. i was totally lost there so i guessed it was produce more of the metal hydroxide.

i said that, because it is a heavier molecule, the same MASS of Ba as Ca = less moles therefore = less H2 produced

Reply 29

sofiakousar

Original post by shaws010

i said that, because it is a heavier molecule, the same MASS of Ba as Ca = less moles therefore = less H2 produced

on the jan op paper there a question identical to this one and the answer was. there would be less Ba to react or some of the barium has already reacted. thats one mark less for me. :frown:

Reply 30

MaeveEllen92

I like this thread :smile:

Thank you to whoever started it..

Original post by fredmc

As a re-taker I found the timing unusually difficult too :frown:

And I did the same for the electronegativity question. GUTTED!

But I think the reactivity decreases down group 2 cause the halides want to gain an electron for a full shell and up the group there is less shielding so increased nucleur attraction so greater pull on other electrons... Is that right does anyone know? :confused:

I think them forces are to do with melting and boiling points?

Reply 31

adilh301

Original post by sofiakousar

nah combined F is always a -1 charge so it would be something like 2f2h2+h20

Reply 32

shaws010

Original post by adilh301

nah combined F is always a -1 charge so it would be something like 2f2h2+h20

would it not be 4HF instead of 2F2H2 (like HCl, not H2Cl2)?

Reply 33

adilh301

Original post by shaws010

would it not be 4HF instead of 2F2H2 (like HCl, not H2Cl2)?

it could be not sure tbh bcoz we dont know if Br and I form the same equation itl probably one of them in the mark scheme and then 'Accept' the other because its only a 1 mark question. im guessing they were looking to knw if u knew the principle of F equalling -1

Reply 34

shaws010

Original post by adilh301

yeah, probably, ik that Br forms HBr and Cl forms HCl but idk bout I

Reply 35

adilh301

Original post by shaws010

yeah, probably, ik that Br forms HBr and Cl forms HCl but idk bout I

what colour did you say the reagent turns when bromine water is added to potassium chloride?

Reply 36

fredmc

I am pretty confident the answer was 2HF to the first part, and GaF3 for the last part :smile:

Another mistake of mine on the last question was to right 3d8 instead of 3d10! Without the time pressure I'd never have done that!

Original post by MaeveEllen92

I like this thread :smile:

Thank you to whoever started it..

As a re-taker I found the timing unusually difficult too :frown:

I think them forces are to do with melting and boiling points?

Yeaaah thats right for ionisation energy definitely, I did consider that answer on Group 7 but I thought that the outermost electrons wouldn't matter as they're gaining electrons, not losing them usually, so wrote Van der Waals instead - _ - To be honest I had 15 seconds left and panicked :P

Reply 37

MaeveEllen92

Original post by sofiakousar

That's the reaction I put if i remember correctly.

F reacts the same as Cl, so I would have thought its just HF :|
But Oxygen goes to 0 cause all elements are oxidation state 0. and H is always +1 so in HF F would be -1. Soo.. It F goes from 0(F2) to -1(HF) andd O goes from -2(H2O) to 0(O2). F has been Reduced and O has been Oxidized .

Reply 38

Yinkx92

This exam was very time consuming. I didnt even have time to check all of my answers again. What did you lot get for the shape of a 5s orbital; was a bit confused there :/