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# A2 OCR Chemistry B F334 - June 2015 watch

1. (Original post by lifeistoff)
Does anyone have any general tips for calculations? I lose hideous amount of marks over them! I am fine with rate, entropy and equilibrium ones, it's just some of the acid ones and the moles/calculating mass ones!
I was having this problem as well, and I found that as soon as I see a calculation, convert everything given in the question into moles. Use formulas like Mass = Mr x Moles and Moles = Concentration x Volume (dm3) and then depending on what the question is use the ratios of moles in an equation to find moles of an unknown and then you can either find it's concentration or mass.

Even if you get everything else wrong, just by converting everything into moles you normally get half the marks. If you want me to go through an example I can do, and I hope this helps
2. (Original post by DJSavjani)
I was having this problem as well, and I found that as soon as I see a calculation, convert everything given in the question into moles. Use formulas like Mass = Mr x Moles and Moles = Concentration x Volume (dm3) and then depending on what the question is use the ratios of moles in an equation to find moles of an unknown and then you can either find it's concentration or mass.

Even if you get everything else wrong, just by converting everything into moles you normally get half the marks. If you want me to go through an example I can do, and I hope this helps
this is exactly what i do!
3. how are you guys feeling about unit 3 and 4?
4. (Original post by nats927)
how are you guys feeling about unit 3 and 4?
Unit 3 and 4? What are they sorry?
5. (Original post by DJSavjani)
Unit 3 and 4? What are they sorry?
what do you mean?? f334 chemistry of materials and f335 chemistry by design.
6. (Original post by nats927)
what do you mean?? f334 chemistry of materials and f335 chemistry by design.
Sorry my bad, I interpreted it as F333 and F334. But I am feeling okay for F335 and good for F334. The only thing I really hate is the NMR and IR identification in F335, never get them right. But I'm so glad that the grade boundaries are relatively low for an A
7. (Original post by DJSavjani)
I was having this problem as well, and I found that as soon as I see a calculation, convert everything given in the question into moles. Use formulas like Mass = Mr x Moles and Moles = Concentration x Volume (dm3) and then depending on what the question is use the ratios of moles in an equation to find moles of an unknown and then you can either find it's concentration or mass.

Even if you get everything else wrong, just by converting everything into moles you normally get half the marks. If you want me to go through an example I can do, and I hope this helps
Thank you so much!

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8. (Original post by lifeistoff)
Thank you so much!

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9. Could somebody explain why things are soluble or insoluble in water in terms of intermolecular bonds? I don't really get it. Is it that more energy is released when bonds are formed between the thing that's dissolving and the water molecules than is required to break the hydrogen bonds between water molecules and imfs between thing that's dissolving??
10. (Original post by BrokenS0ulz)
Could somebody explain why things are soluble or insoluble in water in terms of intermolecular bonds? I don't really get it. Is it that more energy is released when bonds are formed between the thing that's dissolving and the water molecules than is required to break the hydrogen bonds between water molecules and imfs between thing that's dissolving??
The ions become surrounded by water molecules but for intermolecular bonds isnt it just that hydrogen bonds form between molecules. E.g. Nylons are soluble because they have CO-NH in them so between the chains of Nylons you get the highly electronegative atom (oxygen) forming H bonds with the Hydrogen on the other Nylon molecule
11. (Original post by BrokenS0ulz)
Could somebody explain why things are soluble or insoluble in water in terms of intermolecular bonds? I don't really get it. Is it that more energy is released when bonds are formed between the thing that's dissolving and the water molecules than is required to break the hydrogen bonds between water molecules and imfs between thing that's dissolving??
yep. so basically if the energy released from bonds formed b/w water and the 'thing' is greater than the energy needed to break the hydrogen bonds b/w water then its soluble. if more energy needed to break bonds = insoluble.
forming ion-dipole bonds b/w water and the thing is stronger than forming hydrogen bonds b/w water and the 'thing' lol
hope this helps.
12. (Original post by nats927)
yep. So basically if the energy released from bonds formed b/w water and the 'thing' is greater than the energy needed to break the hydrogen bonds b/w water then its soluble. If more energy needed to break bonds = insoluble.
Forming ion-dipole bonds b/w water and the thing is stronger than forming hydrogen bonds b/w water and the 'thing' lol
hope this helps.
ygm fam this is what life is all about innit
13. Ion-dipole forces are just basically hydrated ions in solution... stronger than hydrogen bonding cause ions have either a full positive charge or a negative charge bludd. Hydrogen bonding is an intermolecular force which is also known as as a Permanent dipole-Permanent dipole force bledd.
14. (Original post by GianluigiBuffon)
ygm fam this is what life is all about innit
i get you fam
15. (Original post by nats927)
yep. so basically if the energy released from bonds formed b/w water and the 'thing' is greater than the energy needed to break the hydrogen bonds b/w water then its soluble. if more energy needed to break bonds = insoluble.
forming ion-dipole bonds b/w water and the thing is stronger than forming hydrogen bonds b/w water and the 'thing' lol
hope this helps.
So is it just more energy released in bond formation than is taken in to break the H bonds between water molecules. Or is it more energy released than is taken in to break the H bonds between the water molecules and to break the imfs between thing dissolving too?

(Original post by GianluigiBuffon)
The ions become surrounded by water molecules but for intermolecular bonds isnt it just that hydrogen bonds form between molecules. E.g. Nylons are soluble because they have CO-NH in them so between the chains of Nylons you get the highly electronegative atom (oxygen) forming H bonds with the Hydrogen on the other Nylon molecule
Thanks
16. (Original post by BrokenS0ulz)
So is it just more energy released in bond formation than is taken in to break the H bonds between water molecules. Or is it more energy released than is taken in to break the H bonds between the water molecules and to break the imfs between thing dissolving too?

Thanks
^second one
17. Has everyone received their coursework
scores ?

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18. I received my coursework score the other day

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19. (Original post by pinkgorilla)
scores ?

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no my college dont tell us kmt! but i did find the box with peoples grades.. but not mine . have u?
20. (Original post by pinkgorilla)
scores ?

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yeah got a B according to my teacher

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