OCR F321 - 23rd May

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Eat.Sleep.Row.Repeat.

Here is a list of all the definitions you need to know for tomorrow:

Orbital: regions that can hold up to two electrons with opposite spins.

I hate to sound rude, but that will not get you the mark. The correct definition is:

A region of space where there is a high probability of finding an electron.

That's the one in the book which they base their definitions on!

Edit: Apparently they do allow yours, so sorry for that!

(edited 12 years ago)

Reply 181

ilovedubstep

Original post by intellectual1

Yes if the question asks for

3 marks, they will only mark the first 3 points, even if you have the 4th, 5th points right, the first 3 points only get marked.

5 marks, they will only mark the first 5 points, any more writing and it will be ignored.

It is so harsh with marking now, seems to be a greater test of examination techniques.

Also lets not forget this is just a 60 minute examination.

It'll be easy to medium difficulty, considering Jan11 was considered as a difficult paper.

Do you have a source for this or is it just hearsay?

Reply 182

timkench

Original post by voices1

why is carbon-12 the standard isotope

origanally oxygen was used but chemists used the average of the 16 17 18 isotopes were as physicists used only the 16 isotope leading to discrepancies, so carbond 12 was agreed as the standard

Reply 183

voices1

Is it 3SF for all calculations unless they state otherwise??

Reply 184

The medjai

Original post by Dave_Beeston

I hate to sound rude, but that will not get you the mark. The correct definition is:

A region of space where there is a high probability of finding an electron.

That's the one in the book which they base their definitions on!

No i've actually seen that definition in an exam mark scheme.

Reply 185

lolo-x

Original post by intellectual1

they never told me that at college :frown:

shiiiit. yeah january was pretty hard. oh man, i need to start thinking more positively for tomorrow! haha

Reply 186

timkench

Is it acceptable to bullet point answers? apart from the one at the end where it says fluency of writing will be assessed

Reply 187

Solarity

Original post by voices1

Why are the 1st and 2nd ionisation energies of potassium different??

half equations mite come up. have not seem them in any past papers??

They are different because potassium has one electron in its outermost shell, this electron is the furthest away from the nucleus and has the least attraction from the nucleus because of electron shielding therefore, relatively it doesn't need much energy to be ionised.

Once that electron is removed you need to break into a full shell of electrons to ionise the second electron, its electron configuration would be the same as [Ar]. This shell of electrons are closer to the nucleus so there is a greater pull from the protons in the nucleus as there isn't the extra shielding effect from a previous shell. So relatively a LOT more energy is required to remove another electron from the full shell.

Reply 188

Solarity

Original post by The medjai

No i've actually seen that definition in an exam mark scheme.

Yup just did that past paper where a question asking you to define an orbital came up.

Reply 189

*QueenBeee

how long after the exam are we allowed to discuss answers etc???????????

Reply 190

TrampingRampage

Original post by timkench

Is it acceptable to bullet point answers? apart from the one at the end where it says fluency of writing will be assessed

Examiners actually prefer bullet point answers provided the sentence makes sense.

Good luck everyone taking the exam tomorrow!

Reply 191

Solarity

Original post by voices1

Is it 3SF for all calculations unless they state otherwise??

Thats what i work to, i don't think i've ever seen a question where they ask you for more.

Reply 192

intellectual1

n = V/24 if in dm^3 or if in cm^3 then divided by 24,000

anything in tonnes and kg's must be converted into g's

In solutions n = c x V (in cm^3) / 1000

Remember to look at the mole ratio!

Acids are defined as proton donors

Bases are defined as proton acceptors

HCl Hydrochloric Acid
H2SO4 Sulphuric Acid
HN03 Nitric Acid

Acids have a pH below 7

An alkali is defined as a soluble base that can release hydroxide ions, OH- when in an aqueous solution.

Common bases ie metal oxides Na2O, MgO, CuO metal hydroxides NaOH, KOH, Cu(OH)2 and NH4OH

Salts are fomed as a substance that is formed when one or more H+ ions of an acid are replaced by a metal ion or ammonium ion NH4+

Reply 193

timkench

Original post by TrampingRampage

Examiners actually prefer bullet point answers provided the sentence makes sense.

Good luck everyone taking the exam tomorrow!

yeahh, still after writing two hours of english in the morning, its going to seem really weird aha. Okay, bullet points it is

Reply 194

intellectual1

Original post by ilovedubstep

Do you have a source for this or is it just hearsay?

Read the examiners reports and the textbooks they authored and the student conferences they've spoken at. Similarly some people have got their script back and it shows exactly why they lost marks ie negative marking...

Reply 195

voices1

Original post by *QueenBeee

how long after the exam are we allowed to discuss answers etc???????????

As soon as you come onto STUDENT ROOM. :biggrin:

Reply 196

Solarity

Original post by *QueenBeee

how long after the exam are we allowed to discuss answers etc???????????

Not sure how well this thread is monitored, but for Edexcel Maths that i took last Wednesday they locked the thread until around 3 o'clock the next day any people with clashes that were taking the exam later couldn't find any answers. But for the OCR biology people were talking about it from 3 o'clock the same day.

My guess is that the thread will be locked until any possible candidates sitting it the same day would have finished.

Reply 197

timkench

Ionisation energies across a period
1. greater nuclear charge
2. outer electrons closer to nucleus, smaller atomic radii
3. Same shielding
4. Therefore greater nuclear attraction

Second ionisation energies across a period
1. Removing and electron from a shell closer to the nucleus
2. Stronger nuclear attraction on outermost electron of …..

Bond angles
- Electron pairs repel
- Lone pairs repel more than bonding pairs
- All bonding pairs repel as much as possible
- If molecule is symmetrical dipoles cancel out

ATOMIC RADII

Group
atomic radii increases down group
down group, electrons added to a new shell / more shells
down group, more shielding
increased nuclear charge outweighed / despite increased nuclear charge

Period
atomic radii decrease across period
number of protons/nuclear charge increases
across period electrons added to same shell / same or similar shielding
nuclear attraction increases / shell drawn in by increased nuclear charge

Formation of Bleach
add NaOH2
Cl2 + 2NaOH ?? NaCl + NaClO + H2O