AQA CHEM1: 15th May 2012

on the jan 2012 paper, question 7a, question is: explain why the value you have calculated is slightly different form the relative atomic mass given in the periodic table. Apparently answer is because it takes into account abundances of isotopes, but surely we've just worked out the Mr taking into account abundances of isotopes if we've done it from a mass spec?

can anyone shed some light on this?

it was a meteorite i think the sample was from, and i think the examiner wanted you to say something a long the lines of that its not from earth so the Mr may be different

Reply 201

PaulMc94

Original post by Jack_Smith

Help! I alwas get these questions wrong and its only 1 mark.
http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM1-W-QP-JUN11.PDF
qs 5e help pls=D

fractional distillation isnt it?

Reply 202

SHAH :)

how do you calculate relative formula mass?

Reply 203

Jack_Smith

8

Original post by PaulMc94

fractional distillation isnt it?

question 5E where did fractional distillation come from? Think you reading the wrong question =D

Reply 204

joker12345

19

Original post by SHAH :)

how do you calculate relative formula mass?

Add together relative atomic masses of elements in the compounds. (just saw this in a past paper and had a stress ... then looked it up :smile:

)

Reply 205

wenger16

11

Original post by SHAH :)

how do you calculate relative formula mass?

relative formula mass is just mr of whole molecule. It is mass divided by moles. Its mr of whole molecule.

Reply 206

joker12345

19

Original post by StudentAnon

Indeed!

Still lost for them.. can you say 'trigonal planar' instead of 'trigonal pyramidal' (or whatever the **** it is) when there are three bonded pairs in a molecule with lone pairs? :redface:

I have this issue too! Also, if there are 3 bonding pairs and 1 lone pair is it still tetrahedral?

Reply 207

PaulMc94

Original post by Jack_Smith

question 5E where did fractional distillation come from? Think you reading the wrong question =D

im on the wrong question paper! :colondollar:

Reply 208

Jack_Smith

8

Original post by joker12345

I have this issue too! Also, if there are 3 bonding pairs and 1 lone pair is it still tetrahedral?

Its a trigonal pyramid,
A tetrahedral has four bonding pairs.
3 bonding pairs is trigonal planer.

Reply 209

TaraBelle

10

Original post by PaulMc94

it was a meteorite i think the sample was from, and i think the examiner wanted you to say something a long the lines of that its not from earth so the Mr may be different

oh right okay, thak you! :biggrin:

Reply 210

joker12345

19

Write an equation to show how NO is removed from the exhaust gases in a catalytic
converter. Identify a catalyst used in the converter.

Will they always allow all the different equations ie reacting with C/CO/decomposition?

Reply 211

564767

3

Can anyone think of any dodgy ass questions, of the past or even some that could be asked?

Reply 212

Erotas

Is it worth it or is anyone doing the papers from the past specification?

Reply 213

joker12345

19

State the type of structure shown by crystals of sulfur and phosphorus.
Explain why the melting point of sulfur is higher than the melting point of phosphorus.

Apparently simple covalent isn't allowed and you have to say molecular - does anyone have any idea why this is?!

Reply 214

SHAH :)

Name a process which can be used to separate C5H12 from C6H14

why is it not cracking?

Reply 215

ambrin ox

4

Original post by joker12345

State the type of structure shown by crystals of sulfur and phosphorus.
Explain why the melting point of sulfur is higher than the melting point of phosphorus.

Apparently simple covalent isn't allowed and you have to say molecular - does anyone have any idea why this is?!

I think thats because there is strong covelant bonds within the molecules between the atoms (eg like in iodine) but weak van der waals forces between molecules of iodine, so you have to say simple molecular,

Does anyone know how many marks above an A do you need to get 100 ums? :/ Im really confused,

Reply 216

ambrin ox

4

Original post by SHAH :)

Name a process which can be used to separate C5H12 from C6H14

why is it not cracking?

Both are alkanes and have different chain lenghts so have different boiling points, can use fractional distillation to separate them

Reply 217

Mike Hunt is nice

14

Have finished all the past papers and consistently have been getting between 56-62/70. Should i leave it now and revise for some of my later exams of should i carry on?

Reply 218

juliewho

13

Original post by SHAH :)

Name a process which can be used to separate C5H12 from C6H14

why is it not cracking?

Cracking is to break long chain molecules into short chain molecules, it doesn't separate anything. Fractional distillation is used because that separates different chain lengths because they have different boiling points. :smile:

Reply 219

joker12345

19

Original post by ambrin ox

I think thats because there is strong covelant bonds within the molecules between the atoms (eg like in iodine) but weak van der waals forces between molecules of iodine, so you have to say simple molecular,

Does anyone know how many marks above an A do you need to get 100 ums? :/ Im really confused,

Still don't get why it's wrong to call it a simple covalent structure though :/ and scroll down on here http://web.aqa.org.uk/UMS/index.php and select the year etc, it tells you the raw mars - UMS conversions

AQA CHEM1: 15th May 2012

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