Edexcel Chemistry Unit 1 (23/05/2013)

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does anybody know what the grade boundaries might be like?

In june the grade boundaries do get quite high because a D in June 2012 was apparently an A in Jan 13....

Jan 13 grade boundaries were so low..I hope they stay the same

Reply 21

felicity95

Thank you Jayqwe an Mollymod, that really helps. I was so confused haha :smile:

Reply 22

felicity95

Original post by Ifa_94

Theres no way to predict the grade boundaries. It depends on the difficulty of the paper, and then the marks are UMS'd. for example, I did this exam in june 2012 and got 53 which was a C borderline D and around 70 UMS. In January I found the paper awful and got 39 (bad I know) and still got 70 UMS which is a D. theres no way of predicting. Just aim to do as well as you can :smile:

Reply 23

marseille_h

Is this right:

DeltaHF= DeltaHC(reactants) - DeltaHC(products)
DeltaHC= DeltaHF(products) - DeltaHF(reactants)
DeltaHR= DeltaHF(products) - DeltaHF(reactants)
DeltaHF= DeltaH(bonds brocken) - DeltaH(bonds made)

It worked for me when i practised questions. :biggrin:

Reply 24

Ifa_94

Original post by felicity95

yeh that's true I did this exam last june as well and got 78 ums... really need to do well this time.

good luck :smile:

Reply 25

felicity95

Original post by Ifa_94

yeh that's true I did this exam last june as well and got 78 ums... really need to do well this time.

good luck :smile:

Thank you! good luck to you too!

Reply 26

newyork newyork

explain why the first ionisation energy of aluminium is lower than that of magnesium? someone please help me :smile:

Reply 27

acer0951

Original post by newyork newyork

explain why the first ionisation energy of aluminium is lower than that of magnesium? someone please help me :smile:

The outer electron of Al occupies the 3P sub shell which is a higher energy level compared to Magnesium in which the outer electron occupies the 3S sub shell. The outer electron in Al is further away from the attraction of the nucleus due to greater distance and also greater inner shielding from electrons which again reduces the attractive force of the nucleus on the outer electron therefore the first ionisation energy for Al is lower than Mg.

Hope this helps :wink:

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Reply 28

Minisarah

Any predictions on what might come up in the paper on Thursday?

Reply 29

posthumus

Hey guys

I'm stuck with two things that have been stated in the George Facer book in the the "Bonding" chapter.

Firstly... "There are slight spaces between the metal ions, which are occupied by the delocalised electrons. Therefore, the metallic radius is slightly larger than the ionic radius"

I have no idea why that is, could someone explain :smile:

"d-clock metals use their (n-1)d electrons as well as their ns^2 electrons in bonding" ... does this mean what I think it means that both d & s electrons are used in bonding? Therefore making d-block metals super hard :smile:

Was just confused with the term (n-1)d electrons, what do they mean by that?

And does this mean d-block metals can have like 10 electrons localized... therefore with ions with up to like 10+ charge. It seems unlikely, I think I'm definitely getting something wrong here :tongue:

help !

Thanks in advance to any responses :smile:

Reply 30

davidbaroi

Original post by posthumus

Hey guys

help !

Thanks in advance to any responses :smile:

George Facer books sucks, study edexcel book

Reply 31

muf_mur

Are there any video tutorials available for AS chemistry..especially for the past papers?

Reply 32

Mollymod

Original post by felicity95

Exactly the same as me, but didn't do the January 2013 thankfully.
This is my only retake of unit 1 and I dont need to retake it to get a B, but well I dont want to settle. I'll be happy if I get a B but while it's still possible i still want to aim for the A

Reply 33

Medoo

Do you guys know any of the expected questions for thursday's exam?

Reply 34

amber206

How do you calculate percentage errors?!

Reply 35

felicity95

Hi!

Just another bond enthalpy question. why is the answer to this question A and not C. Surely the mean bond enthalpy is the energy required to break one mole of bonds in the gas phase averaged over many compounds. so then isn't CH4 1 mole, and 1/4CH4 is just a 1/4 mole?

Also if the question had said bond enthalpy as opposed to mean bond enthalpy would it then have been C?

Sorry to ramble on, last minute panic. :s-smilie:

bond enthalpy.png14.2KB

Reply 36

Dragonette

Hey

guys quick questions... can sumone plzzzz explain me question 6,9 and 13.... in the january 2013 unit 1 chemistry paper
these are the mcq questions (clearly)
thanks alot....

Reply 37

amber206

Original post by felicity95

I'm not sure, but it seems C implies that 4 C-H bonds have been broken at once?

Reply 38

felicity95

Original post by amber206

How do you calculate percentage errors?!

% error = Uncertainty in equipment / the reading x 100

the uncertainty is usually given in the question e.g. 0.01, and the for the reading you have to look for what you measured so if you measured the temperature using a thermometer that had a uncertainty of 0.01 and the temperature you measured was say 37.8 then your calculation would be 0.01/37.8 x 100 = + or - 0.026%

If you did more than one measurement i.e. you took two readings etc. you must do 2 x the whole thing.

Hope that made sense :smile:

Reply 39

amber206