OCR B Salters Chemistry 2014 - F332

Does anyone know how to answer those questions when they give you the bond enthalpy then you have to use the Avogadro's constant then then plants constant?

Reply 22

BrokenS0ulz

3

Original post by chemistrykid123

Does anyone know how to answer those questions when they give you the bond enthalpy then you have to use the Avogadro's constant then then plants constant?

Energy needed to break one bond of X:

(bond enthalpy (in kJ) x 1000) / Plank's constant

Frequency needed for this:

v=E/h

= answer to last question / Plank's constant

I love these questions they are a free 5 marks :smile:

Reply 23

Original post by BrokenS0ulz

Energy needed to break one bond of X:

(bond enthalpy (in kJ) x 1000) / Plank's constant

Frequency needed for this:

v=E/h

= answer to last question / Plank's constant

I love these questions they are a free 5 marks :smile:

Okay but what about our man the avogradro doesn't his equation 6.02 (some **** like that) get a mention or is it just about plankz

Reply 24

Original post by chemistrykid123

Okay but what about our man the avogradro doesn't his equation 6.02 (some **** like that) get a mention or is it just about plankz

Avogadro's constant is the number of particles in one mole of a substance.
You could be asked something like: calculate the mass of a single carbon atom. This website has good examples of when the constant is used: http://chemistry.about.com/od/workedchemistryproblems/a/avogadroexampl1.htm

(edited 9 years ago)

Reply 25

Original post by Petulia

Avogadro's constant is the number of particles in one mole of a substance.
You could be asked something like: calculate the mass of a single carbon atom. This website has good examples of when the constant is used: http://chemistry.about.com/od/workedchemistryproblems/a/avogadroexampl1.htm

But..

So the first part of the question radiation required to break a bond is 8.67 x 10¹⁴ calculate he minimum amount of energy to break one bond in J to break the bond.

The second part say calculate the bond enthalpy of the bond in KJ using Avogadro constant

Reply 26

Original post by chemistrykid123

But..

So the first part of the question radiation required to break a bond is 8.67 x 10¹⁴ calculate he minimum amount of energy to break one bond in J to break the bond.

The second part say calculate the bond enthalpy of the bond in KJ using Avogadro constant

The minimum energy required to break a single bond will be (8 x 10^14) / 6.02 x 10^22 (Av constant)
Convert the answer to kJ by dividing by 1000.
Use the constant whenever you're asked about single atoms or single bonds. I think this is the right method.

Reply 27

Totally1337

Original post by chemistrykid123

Does anyone know how to answer those questions when they give you the bond enthalpy then you have to use the Avogadro's constant then then plants constant?

You have to Convert the given bond enthalpy to joules and divide it by
Avogardo constant (6.02X10^23) to find out the energy required to break one bond.

If you are asked to work out frequency you just have to divide to worked out value by planks constant (6.63x10^-34)
E=hf
E/h=f

Reply 28

Original post by Totally1337

You have to Convert the given bond enthalpy to joules and divide it by
Avogardo constant (6.02X10^23) to find out the energy required to break one bond.

If you are asked to work out frequency you just have to divide to worked out value by planks constant (6.63x10^-34)
E=hf
E/h=f

Thank you someone who actually has some brain cells with a clear answer! (unlike the others haha lols)

Reply 29

Fifa97

How would you guys describe hydrogen bonding in ice? Diagrams aren't very clear and wondering how it differs from water? Its on the spec and would definitely be a question that catches people out.

Posted from TSR Mobile

Reply 30

BrokenS0ulz

3

Original post by chemistrykid123

Okay but what about our man the avogradro doesn't his equation 6.02 (some **** like that) get a mention or is it just about plankz

Oops, I mean you divide the first bit by Avogadro's number.

Reply 31

qivo

Original post by Fifa97

How would you guys describe hydrogen bonding in ice? Diagrams aren't very clear and wondering how it differs from water? Its on the spec and would definitely be a question that catches people out.

Posted from TSR Mobile

i don't think we need to know anymore than they both contain hydrogen bonds and that a hydrogen bond is an electrostatic attraction between two partial charges caused by the greater electronegativity of either a nitrogen, oxygen or fluorine compared to a hydrogen. I think the spec just means we need to know they are both examples of hydrogen bonding. But one think that can catch people out is when you draw a hydrogen bond in water that the hydrogen is attracted to one of the lone pairs of electrons around the oxygen and then likewise in similar examples. hope this answers your question

Reply 32

BrokenS0ulz

3

When molecules have very many hydrogen bonds why are they insoluble? Is it about the molecules bonding to themselves instead of the water?

Reply 33

Robbo54

2

Original post by BrokenS0ulz

When molecules have very many hydrogen bonds why are they insoluble? Is it about the molecules bonding to themselves instead of the water?

A polymer will dissolve if the molecules form hydrogen bonds to water.

Too many -OH functional groups, the hydrogen bonds between its molecules will be strong - too much energy is needed to break them down. Therefore the polymer will be insoluble.

Too few -OH groups, there won't be enough hydrogen bonds with water. Polymer will also be insoluble, too.

It's about getting the correct ratio. In exam questions they often ask 'Why does polymer x not dissolve in water' - I don't think we have to know any 'hard limits' of the number of -OH groups.

Reply 34

Tiam.N

Do we need to know batch vs continuous processes? Or do we get given information on them in the test and ask to evaluate it? Haven't seen it crop up in papers that much.

Reply 35

Original post by Tiam.N

Do we need to know batch vs continuous processes? Or do we get given information on them in the test and ask to evaluate it? Haven't seen it crop up in papers that much.

I saw this in the CGP revision guide today and realised that my teacher never even went over this. I briefly read over it and it seems like common sense really, like you could probably think of the advantages and disadvantages on the spot if you had to.

Reply 36

Tiam.N

Original post by Petulia

I saw this in the CGP revision guide today and realised that my teacher never even went over this. I briefly read over it and it seems like common sense really, like you could probably think of the advantages and disadvantages on the spot if you had to.

Thanks for the reply. I know this is a chemistry only thread and I'm going to talk about biology but did you manage to find any of the questions that always came up in unit 2 biology papers? I would really appreciate it if you could let me know so we could strengthen our knowledge on those specific areas. Thanks.

Reply 37

Original post by Tiam.N

Thanks for the reply. I know this is a chemistry only thread and I'm going to talk about biology but did you manage to find any of the questions that always came up in unit 2 biology papers? I would really appreciate it if you could let me know so we could strengthen our knowledge on those specific areas. Thanks.

I was looking at them just the other day and noticed that specific questions aren't repeated for Biology like they are for Chemistry, but I've noticed the same topics / types of questions keep appearing in all of the papers, these are all 4-6 mark topics that I noticed a lot:
- Describing one phase of Mitosis (usually Prophase)
- Acrosome and Cortical Reactions
- Function of sperm cell in relation to structure
- Captive breeding and reintroduction

Practicals that are popular:
- Antimicrobial properties
- Plant tissue culture
Strength of fibres has only come up once that I know of, and that was in last year's paper, so it probably won't come up again.
Questions on mineral deficiencies also appear quite a bit.

Reply 38

Tiam.N

Original post by Petulia

I was looking at them just the other day and noticed that specific questions aren't repeated for Biology like they are for Chemistry, but I've noticed the same topics / types of questions keep appearing in all of the papers, these are all 4-6 mark topics that I noticed a lot:
- Describing one phase of Mitosis (usually Prophase)
- Acrosome and Cortical Reactions
- Function of sperm cell in relation to structure
- Captive breeding and reintroduction

Practicals that are popular:
- Antimicrobial properties
- Plant tissue culture
Strength of fibres has only come up once that I know of, and that was in last year's paper, so it probably won't come up again.
Questions on mineral deficiencies also appear quite a bit.

This is wonderful, thanks very much. Also, whats your prediction for the practical write up that will come up this year? There will 100% be one as there wasn't one in the paper 1.

Reply 39