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Hi,

In OCR AS Chemistry, what do you do with recurring numbers?

Like for e.g. 47.6(recurring). Would it stay as 47.6 or 47.7? I think my chemistry teacher said OCR ignore recurring decimals.
Original post by chuckster111
Hi,

In OCR AS Chemistry, what do you do with recurring numbers?

Like for e.g. 47.6(recurring). Would it stay as 47.6 or 47.7? I think my chemistry teacher said OCR ignore recurring decimals.


Write the recurring answer in your working and then round your answer to whatever decimal place the other figures in the question are given to


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Original post by Sexybadman
Can someone please explain the trends down and across for first ionisations energys and boiling points etc im seriously struggling, also could you explain which deviate from the trend and how mg and Al differ, thanks!:smile:


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Go check chemguide
Anything anyone will write is going to be on it so save everyone's time!
Kk, what past papers should I do. Any common questions that usually come up? Also, how to prepare for section B, or is that just by hammering the past papers and you get a feel for them? Cheeeers
Original post by jshep000
Kk, what past papers should I do. Any common questions that usually come up? Also, how to prepare for section B, or is that just by hammering the past papers and you get a feel for them? Cheeeers


Just do every past paper

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How do you do this question? I did (17.1/342), then multiplied the answer by 6x10^23 and got the answer C?
Original post by jshep000
How do you do this question? I did (17.1/342), then multiplied the answer by 6x10^23 and got the answer C?

There are three sulphate ions per 'molecule' of aluminium sulphate, so multiply your answer by 3 to get D?
Original post by Sexybadman
Can someone please explain the trends down and across for first ionisations energys and boiling points etc im seriously struggling, also could you explain which deviate from the trend and how mg and Al differ, thanks!:smile:


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First ionisation energies increase as you go across the periodic table because
Electrons added to the same she'll
Increased nuclear charge

First ionisation energies decrease down the groups because
More e- so more shells
Outer electrons further from nucleus so can easily be removed
More shielding

Boiling points increase as u go down the groups due to the increase in van der waals (also applies to carbon chains - longer the chain - more van der waals - high boiling point )

Phosphorus and Sulphur deviate because sulfurs outer electrons repel eachother making it easier to remove an electron

Magnesium to Aluminum deviate because Mg outer electrons is is 3s subs hell where as Al is in a higher subshell 3p

Beryllium and Carbon deviate as beryllium outer shell electrons are in 2s subshell and carbons are in 2p subshell (a higher one)
Can someone explain the electrophillic addition of bromine water to cyclopentene? Thanks

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Original post by samwillettsxxx
First ionisation energies increase as you go across the periodic table because
Electrons added to the same she'll
Increased nuclear charge

First ionisation energies decrease down the groups because
More e- so more shells
Outer electrons further from nucleus so can easily be removed
More shielding

Boiling points increase as u go down the groups due to the increase in van der waals (also applies to carbon chains - longer the chain - more van der waals - high boiling point )

Phosphorus and Sulphur deviate because sulfurs outer electrons repel eachother making it easier to remove an electron

Magnesium to Aluminum deviate because Mg outer electrons is is 3s subs hell where as Al is in a higher subshell 3p

Beryllium and Carbon deviate as beryllium outer shell electrons are in 2s subshell and carbons are in 2p subshell (a higher one)


Yoo thanks for taking the time to do this its helped me a lot ! Safe bro 😄


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Original post by purplefoot
When you're testing for halides, I know you would normally add nitric acid and then silver nitrate but what would be the reason for adding the silver nitrate first and then the nitric acid? Any help would be appreciated- just can't seem to think why you would do it that way!


You have to add the Nitric Acid first as this removes any possible interfering ions. If you did this in reverse order a e.g. White precipitate may form but it might not be Silver Chloride like you expect it to be!



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Original post by Sexybadman
Yoo thanks for taking the time to do this its helped me a lot ! Safe bro 😄


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It's ok it helps me remember it having to write it out! You're welcome :smile:
Original post by TeaAndTextbooks
Can someone explain the electrophillic addition of bromine water to cyclopentene? Thanks

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So the double bond repel the electrons in the Br-Br polarising it
The Br-Br bond breaks and the Br closest to the double bond gives up its electrons to the other Br and sticks to the C atom
The other C atom gets positively charged (carbocation)
The Br- then bonds to the positive carbon
It's just the same as you would do electrophilic addition with HBr :smile:
Has anyone get any useful links to videos for balancing equations please. Thatd be awfully helpful
IS anyone sitting the Edexcel AS chem unit 1 June 2015?
Original post by ILOVEA-LEVELS
IS anyone sitting the Edexcel AS chem unit 1 June 2015?


Yes I am
Anyone know where I can find the June 2007 'Foundation' paper mark scheme?
chemdip.png

Can someone explain why dipole dipole is the answer

--> If this was NH4+, or CH4, there wouldn't be any dipoles because the molecule is surrounded by the same delta charge, so another molecule cannot be attracted to it as the like charges on the outside of each molecule will repel them away.

However, with CCl2F2, there is dipole-dipole formation. Why? Is it because of the polarity difference between C-F and C-Cl?
Original post by LibertyMan
chemdip.png

Can someone explain why dipole dipole is the answer

--> If this was NH4+, or CH4, there wouldn't be any dipoles because the molecule is surrounded by the same delta charge, so another molecule cannot be attracted to it as the like charges on the outside of each molecule will repel them away.

However, with CCl2F2, there is dipole-dipole formation. Why? Is it because of the polarity difference between C-F and C-Cl?


Fluorine is more electronegative so gets the delta negative forming a dipole so there is attraction between the opposite charges
Original post by Poole & The Gang
Fluorine is more electronegative so gets the delta negative forming a dipole so there is attraction between the opposite charges


Yes but C-Cl is also polar, and Cl has a negative dipole, and prevents the delta positive charge from interacting with any other molecule?

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