OCR B F335 - Chemistry by Design - 13th June 2012

just did the january 2006 paper, does anyone know the grade boundaries? i cant seem to fins them on the internet....thank youuu

Reply 301

master_blaster66

17

Original post by 12sophie

just did the january 2006 paper, does anyone know the grade boundaries? i cant seem to fins them on the internet....thank youuu

85/120 is for an A ....i found dat paper tough, how did you find it

Reply 302

master_blaster66

17

can halogens be oxidized or reduced?

Reply 303

csefton3

Can anyone give me a hand on dissolving and bonds broken/bonds made? Would really appreciate it. Cheers guys

This was posted from The Student Room's Android App on my GT-I9100

Reply 304

sunshinesmile10

what topics do you think will come up on this exam???

Reply 305

sunshinesmile10

Original post by csefton3

Can anyone give me a hand on dissolving and bonds broken/bonds made? Would really appreciate it. Cheers guys

This was posted from The Student Room's Android App on my GT-I9100

right, Ive just studied this
1. something will only dissolve if the energy taken in when the old bonds are broken is less than the energy given out when the new bonds are made. If not, then the process wont be worth the whole dissolving malarchy :P
2. remember the Intermolecular bonds - PD-PD on dipoles, H bonding when H is bonded to fluorine, oxygen or nitrogen and if in doubt, good ole ID-ID
3. so say what bonds are between the solute and solvent each
4. then say what bonds will be formed eg - ionic-polar between salt and water
5. now say whether the dissolving is possible and talk about the strength of bonding as above..

I think this is it..please correct me if im wrong..

Reply 306

blingmonkeys

How do you work out the pH at the end of jan2012? (very last question)

Reply 307

paul.e.rose

I was wondering how much is the coursework worth in comparison to F335? I really skrewed up the coursework so was wondering how much I need in this exam to come out with a C

Reply 308

Iepnauy

9

Original post by paul.e.rose

I was wondering how much is the coursework worth in comparison to F335? I really skrewed up the coursework so was wondering how much I need in this exam to come out with a C

Coursework - 90 UMS
F334 - 90 UMS
F335 - 120 UMS

For a C you need 180/300 UMS in total over those 3 things.

Reply 309

csefton3

Original post by sunshinesmile10

right, Ive just studied this
1. something will only dissolve if the energy taken in when the old bonds are broken is less than the energy given out when the new bonds are made. If not, then the process wont be worth the whole dissolving malarchy :P
2. remember the Intermolecular bonds - PD-PD on dipoles, H bonding when H is bonded to fluorine, oxygen or nitrogen and if in doubt, good ole ID-ID
3. so say what bonds are between the solute and solvent each
4. then say what bonds will be formed eg - ionic-polar between salt and water
5. now say whether the dissolving is possible and talk about the strength of bonding as above..

I think this is it..please correct me if im wrong..

Ive just spent the last hour trying to get it aswell hahaha! I find it helpful to try and link it to the equation:

Enthalpy change of solution = lattice enthalpy + enthalpy change of hydration

If you remember enthalpy change of hydration is "bonds made" so is exothermic, so is a negative number, and you remember that we actually do -(lattice enthalpy) for lattice enthalpy, then you come out with...

Enthalpy change of solution = lattice enthalpy - hydration enthalpy

So lattice enthalpy (in this case) is pos, endothermic, bonds are broken. And hydration is, neg, bonds are made, so exothermic. Therefore i can conclude:

If hydration enthalpy is bigger (so if energy required to make bonds, is bigger) than the lattice enthalpy, (so energy required to break orginal bonds) Then the overall effect is a negative number.

And when enthalpy of solution is negative. More energy is released in making the bonds (with water for example) then has gone into breaking the original bonds. Therefore they dissolve.

My poorly worded "understanding" anyway :smile:

This was posted from The Student Room's Android App on my GT-I9100

Reply 310

12sophie

8

Original post by master_blaster66

85/120 is for an A ....i found dat paper tough, how did you find it

Okay thanks, do you know what you need in that paper for a B?

Ummm there were a few tricky questions, but i dont think it was that different from the other papers ive done really.

SO scared for this exam :L

Reply 311

master_blaster66

17

Original post by 12sophie

Okay thanks, do you know what you need in that paper for a B?

Ummm there were a few tricky questions, but i dont think it was that different from the other papers ive done really.

SO scared for this exam :L

i think it was 76-78

Reply 312

master_blaster66

17

if anyone wants to do a easy paper then do the june 2006 paper which is very easy compared to other ones but has a lil bit higher grade boundaries, 90/120 for an A

Reply 313

sunshinesmile10

Original post by master_blaster66

if anyone wants to do a easy paper then do the june 2006 paper which is very easy compared to other ones but has a lil bit higher grade boundaries, 90/120 for an A

I thought everyone found this one hard...are you being sarcastic?

Reply 314

hash007

15

Original post by master_blaster66

85/120 is for an A ....i found dat paper tough, how did you find it

It was quite hard, but I got 97/120 :biggrin:

Hope the grade boundaries for this paper are low because I always seem to do well in past papers, then mess up the actual thing!

Reply 315

hash007

15

Original post by csefton3

Can anyone give me a hand on dissolving and bonds broken/bonds made? Would really appreciate it. Cheers guys

This was posted from The Student Room's Android App on my GT-I9100

Looking at the mark schemes all you have to do is compare the type of imf in each compound, and say which bonds are broken.

E.g.

Water is bonded to molecules of itself by hydrogen bonds.
Sodium Chloride has ionic bonds.

Then say which bonds are broken/which are made.

Ionic bonds break to form ions in solution, which bond to molecules of water. They form ion-dipole bonds.

If the bonds made are of similar strength, the compound will dissolve.

The ion-dipole bonds made, compensate for the energy required to break H bonds in water. Or the ion-dipole bonds are of similar strength to H bonds in water so they dissolve.

Reply 316

CustardDoughnut

Original post by Bi0logical

Thanks I understood that, so we were left with moldm-3 on the top right?
But what if we're left with moldm-3 at the the bottom? how come sometimes its mol-2dm6 or whetever (when it's minus)

Thanks in advance

If it's (moldm^-3) x (moldm^-3) that will be (mol^2dm^-6)

If you're left with 1/(moldm-3) then you swap the power signs. So you'll get mol^-1dm^3

Reply 317

Dixie

just wondering, how far back are people going in terms of papers? coz the f335 stop in june 2010 i think so how many legacy papers are people doing?

Reply 318

minip12qss

(f) A student sets out to make a buffer solution. The student measures out 27 cm3 of
0.050 mol dm–3 HA solution and reacts it with one-third of the volume of 0.10 mol dm–3 sodium
hydroxide needed for complete neutralisation.
(i) Calculate the volume of sodium hydroxide solution that the student uses.
volume = ................................................. cm3 [1]
(ii) Calculate the pH of the resulting buffer solution.
Ka = 9.3 × 10–4 mol dm–3
pH = .......................................................... [1]
How would anyone do these questions

(edited 11 years ago)

Reply 319

Bi0logical

7

Original post by CustardDoughnut

If it's (moldm^-3) x (moldm^-3) that will be (mol^2dm^-6)

If you're left with 1/(moldm-3) then you swap the power signs. So you'll get mol^-1dm^3

So if you cancelled some out, and you have (moldm^-3) x (moldm^-3) left on the bottom , its mol2dm-6 right?

I understand the first bit but what do you mean by the "1 / moldm-3"? why is there a 1?

OCR B F335 - Chemistry by Design - 13th June 2012

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