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# Ocr f321 23 may 2013~official discussion thread Watch

1. (Original post by CRW1996)
What answer did every get for the water of crystallisation calculation?

16
2. (Original post by Brookie95)
Think I just got Cl-, wouldn't ClO be 3-?
nope its -1 chlorine would be 1+ instead of 2-
3. (Original post by Brookie95)
Think I just got Cl-, wouldn't ClO be 3-?
Not in this case. Since we know Na has to be 1+, it means that ClO has to be 1-, so here oxygen is -2 and chlorine is +1.

edit: (since chlorine has a number of oxidation states)
4. I can't work out if it was hard or average so many diff answers for diff things
:L

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5. (Original post by Happy03)
I can't work out if it was hard or average so many diff answers for diff things
:L

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exactly :/
6. (Original post by Harryshah)
16
YAY I got that to...
7. i think this exam was pretty tricky, seems like it was written to trip candidates up
8. (Original post by kelvinbeyioku)
nope its -1 chlorine would be 1+ instead of 2-

(Original post by theCreator)
Not in this case. Since we know Na has to be 1+, it means that ClO has to be 1-, so here oxygen is -2 and chlorine is +1.

edit: (since chlorine has a number of oxidation states)
Thanks, glad it was only one mark
9. i just realised this paper was to trip people up for example: NH3 PH3
what intermolecular forces(between atoms) are present so its hydrogen and dipole tto dipole but now they asked whys the melting point higher,this tricks you because now you talk about the forces between molecules,NH3 has hydrogen bonds that are stronger than the vaan deer walls between Ph3 molecules,makes sense
10. Damn you OCR! Managed to trick me alright...
11. (Original post by jackitsme)
i just realised this paper was to trip people up for example: NH3 PH3
what intermolecular forces(between atoms) are present so its hydrogen and dipole tto dipole but now they asked whys the melting point higher,this tricks you because now you talk about the forces between molecules,NH3 has hydrogen bonds that are stronger than the vaan deer walls between Ph3 molecules,makes sense
I thought intermolecular forces are between the molecules, such at H bonds, VDW, Dipole-dipole, not atoms.
The intramolecular forces would be covalent.
12. (Original post by kelvinbeyioku)
are you aiming for an a ?
Yeah, are you?
13. hi guys, I did the F321 paper today and I must say it was weird - both easy and hard. some questions were straightforward but some of the unknown compounds just made me really nervous, eg the bonding in NH3BF3, oxidation of P in N2H2PO4?
I did almost all of the past papers before, knew the syllabus and the content of the book outside out and still got a lot of questions wrong or I am uncertain about. I hope the grade boundaries could be 49/50 for an A...
14. Just can't wait for the Unoffical Marksheme. Think I've made many mistakes
15. (Original post by Liberty.)
I thought intermolecular forces are between the molecules, such at H bonds, VDW, Dipole-dipole, not atoms.
The intramolecular forces would be covalent.
yep sorry ment inter for hydrogen and dipole-dipole

intra hydrogen and vaanderwaals

i dont know im confused now

i wrote
:
for the table Hydrogen bonding and vaan der walls
then i said how hydrogen bondings stronger than VDW

apparently im wrong?
16. (Original post by MathsNerd1)
Yeah, are you?
yeah but i have to get 133 raw marks in these two exams as igot 27/40 in my course work :/
17. (Original post by jackitsme)
yep sorry ment inter for hydrogen and dipole-dipole

intra hydrogen and vaanderwaals

i dont know im confused now

i wrote
:
for the table Hydrogen bonding and vaan der walls
then i said how hydrogen bondings stronger than VDW

apparently im wrong?
Stupidly enough I put dipole-dipole for NH3 and VDW for PH3 .
But you're right in saying H bonds triumph VDWs surely...
18. (Original post by kelvinbeyioku)
yeah but i have to get 133 raw marks in these two exams as igot 27/40 in my course work :/
That's unfortunate really and mine is for my A2 levels to push my current C upto an A.
19. omg. im just dont know. i felt good after the exam, then remember all my mistakes.ive definitely drop 4-6 that i know of.assuming everything else is right...time was my enemy
20. (Original post by jackitsme)
yep sorry ment inter for hydrogen and dipole-dipole

intra hydrogen and vaanderwaals

i dont know im confused now

i wrote
:
for the table Hydrogen bonding and vaan der walls
then i said how hydrogen bondings stronger than VDW

apparently im wrong?

I think you are right because the question was: why does NH3 have a higher melting/boiling point? Melting point is connected with intermolecular forces, in this case hydrogen bonding is much stronger than van der waals or dipole-dipole forces. Hydrogen bonding is extra force over and above van der waals/dipole-dipole.

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