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# Ocr f321 23 may 2013~official discussion thread Watch

1. (Original post by Funtry)
No problem, you may have gotten a mark for VDW forces, as everything technically has slight VDW forces between them, but I'd doubt you'd get full marks. Was it a 1 or 2 mark question?
There was 2 bits to it so the table and then the explanation for why NH3 's mp was higher so in total it was 2 marks I'm hoping I got ECF though
2. (Original post by Zakee)
I think one mark was for n = m/RMM, one mark was for multiplying by avagadro's, and also one mark was to show whether or not you realized what a mole actually was an you didn't need to multiply by 4.
Makes sense, I think I forgot to write down a formula or two (as in n=m/Mr), but oh well
3. In regards to the number of molecules, I think the mass given was 8.624 or 8.648 (don't take my word for it) and the molecule was SiCl4 which has a Mr of 170.1 (28.1+142).
4. (Original post by Funtry)
Yes, as you can almost treat the molecules as atoms if you like. If you had 1 mole of Helium atoms, it would be the same number of molecules as 1 mole of O2 molecules and yet twice the number of atoms. It asked for the number of molecules not atoms.
Does multiplying the number of moles by avagadro's constant give you the number of atoms? I don't understand why that's the same as the number of molecules.

I'm not complaining, of course, because if you're right, I got the question right. I'm just curious, that's all.
5. (Original post by Nermin Hayek)
There was 2 bits to it so the table and then the explanation for why NH3 's mp was higher so in total it was 2 marks I'm hoping I got ECF though
Ah yeah, fingers crossed!
6. (Original post by Funtry)
That's what I got

Seemed too little for 3 marks!
i found 0.05 as the mol and then i x5 because there was 5 molecules in SiCl4 then i got 0.25 which i then x it by the avogadro number and i got 1.505x10^23 correct me if im wrong i want to see why its not that
7. (Original post by Funtry)
No problem, you may have gotten a mark for VDW forces, as everything technically has slight VDW forces between them, but I'd doubt you'd get full marks. Was it a 1 or 2 mark question?
Reason why I don't think a mark will be awarded for VDW is because the heading of the table specifically stated 'main type of bonding' acknowledging the fact that both PD-PD and VDW will be present. I myself put VDW =\, yet again didn't read through the question propperly.
8. Would I get the mark for stupidly putting concentrated ammonia 'solution' rather than just concentrated ammonia

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9. (Original post by Annie_o)
Would I get the mark for stupidly putting concentrated ammonia 'solution' rather than just concentrated ammonia

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Should be fine.
10. (Original post by Annie_o)
Would I get the mark for stupidly putting concentrated ammonia 'solution' rather than just concentrated ammonia

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yeah.it has to be in aqueous state. solution I believe would be accepted
11. (Original post by Ferrari_1996)
Does multiplying the number of moles by avagadro's constant give you the number of atoms? I don't understand why that's the same as the number of molecules.

I'm not complaining, of course, because if you're right, I got the question right. I'm just curious, that's all.
no. A mole is a constant (6.02x1023), and so if you have say 1 mole of something (ANYTHING), you will have 6.02x1023 of it. That can be atoms, molecules, grains of sand, planets, anything. So if you have 0.05 moles of SiCl4, then to find the number of molecules, you have to times AGadro's constant by the number of moles.
12. I thought the gas was 360 ... what's this about 1080I?
13. (Original post by scorpio22)
u thought the gas was 360 ... what's this about 1080?
It's definitely 360 because it was multiplying the mole ratio by 3 not the final volume
14. Does anyone have any tips on coping with the timing for this exam? I don't feel 1 hour is enough at all.
15. (Original post by Geronimo!)
i found 0.05 as the mol and then i x5 because there was 5 molecules in SiCl4 then i got 0.25 which i then x it by the avogadro number and i got 1.505x10^23 correct me if im wrong i want to see why its not that
Incorrect, unless it was asking for the number of atoms (which is wasn't I don't think). A mole doesn't always apply to atoms (see previous post).
16. (Original post by Funtry)
no. A mole is a constant (6.02x1023), and so if you have say 1 mole of something (ANYTHING), you will have 6.02x1023 of it. That can be atoms, molecules, grains of sand, planets, anything. So if you have 0.05 moles of SiCl4, then to find the number of molecules, you have to times AGadro's constant by the number of moles.
Ok thanks for the information. Yay, I got the question right. Enjoy the rest of your day
17. (Original post by Daniel__)
Reason why I don't think a mark will be awarded for VDW is because the heading of the table specifically stated 'main type of bonding' acknowledging the fact that both PD-PD and VDW will be present. I myself put VDW =\, yet again didn't read through the question propperly.
Ah yeah, that would be a bummer.
18. (Original post by Funtry)
no. A mole is a constant (6.02x1023), and so if you have say 1 mole of something (ANYTHING), you will have 6.02x1023 of it. That can be atoms, molecules, grains of sand, planets, anything. So if you have 0.05 moles of SiCl4, then to find the number of molecules, you have to times AGadro's constant by the number of moles.
Thanks for clearing this up.. I was wondering this myself I ended up with the number of moles, should only lose 1 mark since Avagadro's Constant is given in the formula booklet?
19. Will you get ecf for the dipole-dipole question.
Its 1080cm3
20. (Original post by Ferrari_1996)
Does multiplying the number of moles by avagadro's constant give you the number of atoms? I don't understand why that's the same as the number of molecules.

I'm not complaining, of course, because if you're right, I got the question right. I'm just curious, that's all.

yh multiplying number of moles by avagadro's constant should give you number of molecules. If you then multiplied THAT number by the number of atoms in the SiCl4 molecule (i.e. 5) then that would give you number of atoms. But it sounds like you got it right nyway.

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