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Edexcel AS Chemistry: 4th June 08

E.M.C.

callum9999

Thats what I put and I've never seen it before either. I also mentioned something about charge density to try and "pad out" my answer but I don't know if that matters?

Has anyone here sat the January 08 papers (or did them during revision)? Did you find these exams easier, harder or about the same?

I wrote the stuffs from unit 4, about the sum of the ionic radii being greater for NaI than that for NaCl, so attraction is less so less energy needed to separate Na ions and I ions.

And yes,i did do jan 08.was easy, units 1 n 2 of this time were easier than jan08, but unit 3B this time was harder, weirder, and God knows why i lost concentration during unit 3, during revising i found so many silly mistakes! and i totally forgot what on earth a separating funnel looks like!! couldnt even imagine it! made lots of other stupid mistakes. oh! who ever thought chemistry would ever be this disappointing!

(well, just as an excuse--i had biology the day before so could hardly study chemistry.. would the examiner give me marks for that???)

:frown:

Reply 221

harvieb

Trampmaster90

hey all

was wonderin wat every1 got for the percentage oxidised question?
i got around 9.4%

cheers

Mate thats exactly what i got

0.217mdm / 2.25dm x100= 9.64%

Also the next question about the why this is not accurate measurement of h+ ions or acidic content in the wine

i wrote that because ethanoic acid only partially dissociates in solution, therefore the h+ ion concentration would be less than 9.64%?

Alot of people wrote that because the colour change would be the same colour as the wine, forgetting to read that the wine was white, and the colour change is from colourless to pink, so i didnt think that was right.

also i dont think that the argument that other products are contained in the solution, as it said it was ethanol, and therefore can only oxidise to ethanoic acid... so you tell me loll....

any ideas?

Reply 222

harvieb

callum9999

I think its right. If I remember correctly, the only other substance in the solution had a boiling temperature of at least 60 degrees, therefore going over by 1 degree isn't going to cause any contamination. I think I also remember seeing an answer like this in a markscheme. Sorry I can't be certain but does it really matter now? Its too late to do anything about it.

its 49-53 as the boiling temp was 51 degrees, basically 2 degrees either side the boiling point, saw dat in some previous paper...

Reply 223

fn137

11

harvieb

Mate thats exactly what i got

0.217mdm / 2.25dm x100= 9.64%

Also the next question about the why this is not accurate measurement of h+ ions or acidic content in the wine

i wrote that because ethanoic acid only partially dissociates in solution, therefore the h+ ion concentration would be less than 9.64%?

Alot of people wrote that because the colour change would be the same colour as the wine, forgetting to read that the wine was white, and the colour change is from colourless to pink, so i didnt think that was right.

also i dont think that the argument that other products are contained in the solution, as it said it was ethanol, and therefore can only oxidise to ethanoic acid... so you tell me loll....

any ideas?

I don't want to disappoint you but then what you wrote is wrong and when I read your post I was staring at it stunned thinking my answer and many of others is wrong. You have miss read the question.
The experiment in the question used "white wine" but in the question they are asking why is this method unsuitable to be used with "red wine" ? And the answer is because its impossible to find the endpoint because the colour change cannot be observed.
If you want to confirm this, you can check out the paper, someone has posted it on page 2 of this thread.
Sorry! :frown:

Reply 224

urban_flavaz

For unit2: Give the formula of an alkane, containing more than one carbon atom, whose
molecular and empirical formulae are the same.

i wrote C5H12

is that wrong =$ ???

Reply 225

Trampmaster90

2

shuld be fine, I asked my teacher and he sed tht any chain with an odd number of carbon atoms will work. So the C5 tht u put is prefectly good.

Reply 226

jsp13

sorry lame question but in unit one what was the bond between O and H in the Metal Complex? i think it was the second part of the question....

Reply 227

fait

OP

O-H bond was covalent and the O-Mg bond was dative covalent, I think.

Reply 228

Oxy

14

fait

O-H bond was covalent and the O-Mg bond was dative covalent, I think.

O-Mg isnt it an ionic bond?

Reply 229

fait

OP

No it's dative covalent. I'm pretty sure because there was 6 arrows pointing to the central Mg2+ ion.

Reply 230

jsp13

yup it was dative because each O donates one of its lone pairs to Mangnesium
but for O-H i wrote hydrogen Bond/ Covalent Bond ... will i loose the mark?

Reply 231

Aisha_s

yeh does anybody know how UMS is calculated ??

Reply 232

fn137

11

Mg+2 ion ...it was a complex ion ......so in them the ligands (in here the O-H) are always bonded with dative covalent/co-ordinate bonds. Mg+2 ion has empty orbitals and there r lone pairs of electrons on the oxygen atoms of the water molecules.
Mg+2(H2O)6 hexaaqua magnesium 2 ion.
O-H : Covalent bond
Mg-A : Dative covalent bond

Reply 233

harvieb

fn137

I don't want to disappoint you but then what you wrote is wrong and when I read your post I was staring at it stunned thinking my answer and many of others is wrong. You have miss read the question.
The experiment in the question used "white wine" but in the question they are asking why is this method unsuitable to be used with "red wine" ? And the answer is because its impossible to find the endpoint because the colour change cannot be observed.
If you want to confirm this, you can check out the paper, someone has posted it on page 2 of this thread.
Sorry! :frown:

loll ma bad... its kooll dou onli 1 mark... i fort i mite be smart and pull some unit 4 knowledge... lmao... but even so red wine, is red isnt it... whereas phenolphathlein is pink, with a white tile surely theres a distinct and obvious difference, as you do titrations similar... not really sure about that... becus once all red wine is reacted, the phenolphathlein kicks in immediately, and goes light pink, doesnt remain red?

Reply 234

Oxy

14

fait

No it's dative covalent. I'm pretty sure because there was 6 arrows pointing to the central Mg2+ ion.

You didnt say it was dissolved in water, i didnt do that unit 1 paper so i just took information from your post

And the way UMS is calculated changes every year, depends on how well everyone did on the whole.

Reply 235

fn137

11

http://www.thestudentroom.co.uk/showthread.php?p=12755602#post12755602

7th post ...someone has written a sort of formula by which they do this UMS calculation.

Reply 236

redsox20

Hi

Sorry to revive the thread, just wanted to know, for the definition of empirical formulae, if I put ratio, instead of simplest ratio, would I still get the marks?

Thanks

Reply 237

fait

OP

Dunno. Some chemistry mark scheme can be really precise so they wouldn't give it. You might do, though.

Actually, you reminded me about that question: Did you guys write about simpliest
ratio of elements in a substance OR simpliest ratio of atoms in a substance? I wrote about elements, I think I got that wrong. Man, I'm really starting to get paranoid about this exam...

Reply 238

Oxy

14

redsox20

Hi

Sorry to revive the thread, just wanted to know, for the definition of empirical formulae, if I put ratio, instead of simplest ratio, would I still get the marks?

Thanks

No

Reply 239

redsox20

Ahh ok, thanks.

Mind if I ask one more?

What products do you think they will accept for the oxidation by potassium dichromate of the diol.

Thanks

Edexcel AS Chemistry: 4th June 08

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