AQA CHEM1: 15th May 2012

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What did everyone get for the calculations in question 5? I saved the answers in my calculator.. Got 2.81g for the first one, 2.21mol/dm^3 for the next one, 8.98% for the atom economy and B2Cl4 for the molecular formula one.
Thought it was an ok paper but I panicked in the same way I did in January because I was running out of time..

Exactly what i got :biggrin:

But I didn't understand why i got my answer for the concentration though. I did
moles of HCL divided by 500*10^-3
but isn't the 500cm^3 the volume of the whole solution? I was running out of time so I wrote it down as my answer anyway, but I'm still confused.

Reply 521

berryripple

I was relying on this to pull up my unit 2 :frown:

Reply 522

Pinkhead

Original post by jodiedoodles

What did anyone put for the structure of titanium? And also, on the one where you had to use the ideal gas equation, did you divide the moles by 5 then work out mass as there was 5 moles of product and we wanted it for one mole of reactant? Got myself really confused!

Thanks :smile:

I said that titanium is metallic, and yes, you had to divide by number of gas moles, which was 5 :smile:

Reply 523

erniiee

Was this easier than Jan?

Reply 524

alex7892

Original post by Pinkhead

Isn't Boron diatomic? so it should be B2 + 3Cl2 ----> 2BCl3

I'm not sure as on the next question it was saying pure boron iss formed and its chemical formulae was just B , so i'm not sure :s-smilie:

Reply 525

Pinkhead

Original post by radardetector

boron can be both monatomic and diatomic :smile:

So which one would be the right equation? :s-smilie:

Perhaps they'll have 2 possible options?

Reply 526

radardetector

Original post by Pinkhead

So which one would be the right equation? :s-smilie:

Perhaps they'll have 2 possible options?

yeah will give both answers in mark scheme and will allow any multiples :smile:

Reply 527

Millyshyn

Original post by Pinkhead

Exactly what i got :biggrin:

Yeah, you work out the concentration of HCl in the mixed solution.
Are you sure you divided moles of HCl and not moles of BCl3? Because it didn't give you the mass of HCl to work out the moles with.

Reply 528

Pinkhead

Original post by erniiee

Was this easier than Jan?

Yes, I found this one tougher, but I didn't really find Jan 2012 to be that hard, so it might not be a very representative opinion

Reply 529

alex7892

Is anyone making an unofficial mark scheme?

Reply 530

neeloo

Just waiting for someone to post one of those unofficial markscheme things..

Reply 531

Pinkhead

Original post by Millyshyn

Yeah, you work out the concentration of HCl in the mixed solution.
Are you sure you divided moles of HCl and not moles of BCl3? Because it didn't give you the mass of HCl to work out the moles with.

The ratio of HCl to BCl3 was 3:1 because it was 3HCL.
So I worked out the moles using the mass, and multipied by 3.

Reply 532

Abbieastoria

Neeloo, not neccisarily the questions. But the whole format of the paper. Maths and the end and then loads of little 1 mark hydrocarbon questions

Reply 533

Zytex

Did anyone get this for the equation of boric acid with sodium hydroxide?

H3BO3 + 3NaOH ---> Na3BO3 + 3H2O

Reply 534

sososososxc

Unofficial Mark Scheme anybody ?

Reply 535

Millyshyn

Original post by Zytex

Did anyone get this for the equation of boric acid with sodium hydroxide?

H3BO3 + 3NaOH ---> Na3BO3 + 3H2O

Yeh, I got this as well.

Reply 536

jodiedoodles

Original post by Pinkhead

I said that titanium is metallic, and yes, you had to divide by number of gas moles, which was 5 :smile:

Aaah I put titanium was hexagonal close packed structure, as it said it had bonding similar to magnesium which is hexagonal close packed :frown:

Reply 537

neeloo

Original post by Abbieastoria

Neeloo, not neccisarily the questions. But the whole format of the paper. Maths and the end and then loads of little 1 mark hydrocarbon questions

oh right, normally I find the calculations difficuilt too because I make small mistakes or punch the wrong things in to my calculator lol but this time I found the last question were fine, pv=nrt questions made me think though since one gas had 3 mole and the other 5 it gave you the the total volume? ANh yeah I found those one markers weirs, what did you write as the reagent?

Reply 538

Philippamalko

Original post by lochbeau

Think I got completely difference answers to this which is quite scary, wasn't confident about the calculations either :frown:

I got 14% for the atom economy, 14.06g and I can't even remember the mole one.

for the 14.06g one did you not divide the number of moles found with pv=nrt by 5 as it was the moles for all the gases produced (5 molecules) and use that to find out the mass? i got around 14g the first time then read the question again and got around 2g or something