OCR Chemistry A 2017 Exam Thread (New A Level)

hey does anyone know when to use the following purification techniques, like how do you decide which one of the following to use:
- distillation
-reflux
- separating funnel
-filtration under reduced pressure
- recrystallisation
thanks so much in advance

Reply 381

hashman

13

Original post by medicapplicant

hey does anyone know when to use the following purification techniques, like how do you decide which one of the following to use:
- distillation
-reflux
- separating funnel
-filtration under reduced pressure
- recrystallisation
thanks so much in advance

distillation when separating substances with two boiling points
reflux during oxidation (full oxidation) eg forming carboxylic acid
seperating funnel during purifying an organic liquid
filtration under reduced pressure purifying organic solid

Reply 382

Yeahwhat

22

Has anyone got the 2016 Breath and Depth papers? I can give you all of the set 2 papers in exchange.

Reply 383

jossiche0426

2

Hey guys do u think the 2017 papers will have biofuel production/advantages and disadvantages, greenhouse gases and stuff??? And CCS technique??

Reply 384

nivibilla

6

Original post by jossiche0426

Hey guys do u think the 2017 papers will have biofuel production/advantages and disadvantages, greenhouse gases and stuff??? And CCS technique??

As you start preparing for the Depth paper, it will be useful to focus on the following topics as they were not assessed in detail in today’s exam and very likely appear in the next one:

1.

All organic reaction mechanisms-

•

Free radical mechanism

•

Electrophilic addition

•

Nucleophilic substitution

1.

Practical skills based on test for ions and identification

2.

Calculations based on Q=mc∆T and enthalpy calculations

3.

graphical method for calculating rate of reaction by drawing tangents

4.

oxidation reactions of alcohols

5.

spectroscopy:

•

IR and mass spectra questions (long answer style)

1.

Structure and bonding:

•

Predicting the bond angle based on number of lone pairs and shared pairs of electrons

•

Dot and cross diagrams for ionic and covalent (and dative covalent) bonds

•

Comparing and identifying properties of given compounds based on the bonding type and intermolecular forces

•

H-bonding in water and anomalous properties of water

1.

Percentage yield calculations

2.

Energy profile diagrams for endo and exothermic reactions (labelled diagrams)

3.

Le Chatelier principle and position of equilibrium

4.

Reactions of group 17- displacement (ionic equations) and disproportionation

Enjoy the revision and see you after the half term!Thanks

our teacher did this

Reply 385

neza99

4

Original post by DisturbedCustard

Think this is right. If you need furher explanation ask here or drop me a dm.

Hiya, can you help me with this question please? i got 4H2S + 3O2 = SO2 + 3S + 4H2O. I thought you had to cancel the similar compounds then just add the res? but the answer on the ms is very different. Thanks!

Screen Shot 2017-06-06 at 12.05.09 AM.png

Screen Shot 2017-06-06 at 12.05.09 AM.png

Reply 386

S.G.

22

Original post by neza99

Hiya, can you help me with this question please? i got 4H2S + 3O2 = SO2 + 3S + 4H2O. I thought you had to cancel the similar compounds then just add the res? but the answer on the ms is very different. Thanks!

Screen Shot 2017-06-06 at 12.05.09 AM.png

2 SO2 is produced in the first equation so you need to multiply the second equation by 2 as you only have 1 SO2 and then add them together. I think you can then cancel down to get the answer.

Reply 387

neza99

4

Original post by SGHD26716

2 SO2 is produced in the first equation so you need to multiply the second equation by 2 as you only have 1 SO2 and then add them together. I think you can then cancel down to get the answer.

Thanks!

Reply 388

S.G.

22

Original post by neza99

Thanks!

Did that get the right answer?

Reply 389

neza99

4

Original post by SGHD26716

Did that get the right answer?

yup!

Reply 390

DisturbedCustard

8

Original post by neza99

Hiya, can you help me with this question please? i got 4H2S + 3O2 = SO2 + 3S + 4H2O. I thought you had to cancel the similar compounds then just add the res? but the answer on the ms is very different. Thanks!

Screen Shot 2017-06-06 at 12.05.09 AM.png

So sorry just saw this now. But yes i agree with the person who helped you. If you need anything, just ask and hopefully ill respond asap if i know!

Reply 391

Keira44556

3

Any predictions on what is very likely to come up? For example things that are new to the spec and things that weren't on the breadth/depth papers?

Reply 392

Keira44556

3

Also, another question, will we be tested on PAG experiments if they aren't in the book?

Reply 393

ToriSomoye

Can someone please go over ionisation energies and how it links to electron affinity and electronegativity ?

Posted from TSR Mobile

Reply 394

oni176

7

Original post by ToriSomoye

Can someone please go over ionisation energies and how it links to electron affinity and electronegativity ?

Posted from TSR Mobile

For ionisation energies, you need to mention the general trend across period and down a group, making references to atomic radius, nuclear charge, shielding and the affect on nuclear attraction.
You also need to talk about the reason for decrease in first ionisation energies between groups 2 and 3 as well as groups 5 and 6. For 2+3 you need to state that there are p orbitals containing higher energy than s orbitals, causing a decrease in nuclear attraction..
5+6 = Oxygen for example have shared pair of electrons than nitrogen, causing repulsion of p-orbitals which causes a decrease in nuclear attraction.

You also need to know how a particular element shows evidence for its structure by talking about which shells have a large increase in ionisation energies etc. Then you can state how many electrons in the outer shell etc...

(edited 6 years ago)

Thank you very much

Does anyone have a definitive list of the tests we have to know (particularly for the physical exam on tuesday). Any help would be greatly appreciated!

Reply 397

S.G.

22

Original post by DashingPenguin

Does anyone have a definitive list of the tests we have to know (particularly for the physical exam on tuesday). Any help would be greatly appreciated!

Last page in the CGP revision guide on Module 5 has all of them including module 3 tests.

Reply 398

oni176

7

Original post by DashingPenguin

Does anyone have a definitive list of the tests we have to know (particularly for the physical exam on tuesday). Any help would be greatly appreciated!

Carbonate, sulfate, ammonia, halogens, Precipitation reactions (Cu, Fe2+, Fe3+, Mn2+ and Cr3+), ligand substitution between chromium and ammonia, copper with ammonia and copper with hydrohloric acid. You need to memorise the ionic equations too.