A2 OCR Chemistry B F334 - June 2015

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

how are you guys feeling about unit 3 and 4?

Unit 3 and 4? What are they sorry?

what do you mean?? f334 chemistry of materials and f335 chemistry by design.

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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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??

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.

ygm fam this is what life is all about innit

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.

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

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

Has everyone received their coursework
scores ?


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Has everyone received their coursework
scores ?


Posted from TSR Mobile