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Aqa chem 4/ chem 5 june 2016 thread

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Hey guys, just wanted to say that if anyone wanted a quick summary on everything you need to know for the course as a bit of last minute revision stuff then I made a thread. Don't know if it'll be useful but here:

http://www.thestudentroom.co.uk/showthread.php?t=4159211

Anyway good luck, hope it goes well for you all. :woo:

Reply 521

Kaya22

the questions with excess OH- come up loads. you just use kw

Reply 522

Ultracrepidarian

Original post by Anon_98

legend, will you be doing the same for unit5?

Reply 523

Jpw1097

You would use the base dissociation constant, K_b, if there was an excess of a weak base. If there is an excess of a strong base, you just use K_w, to find [H⁺]. However, we are not tested on questions using K_b, it's either an excess of weak acid or an excess of a strong base.

(edited 7 years ago)

Reply 524

Kaya22

Original post by Jpw1097

You would use the base dissociation constant, K_b, if there was an excess of a weak base. If there is an excess of a strong base, you just use K_w, to find [H⁺].

oh well if its weak base it wont come up as that isnt on the spec at all so i wouldn't worry about kb

Reply 525

nutcase13

Original post by Hadigy

Guys - look out for properties of fats/oil, m+4 peak, chromatography, converting sodium salts back to fatty acids, half equivalence, aspirin, dative covalent bonding amines, properties of amino acids as solids and liquids, disposing polymers, diprotic acids.

m+4 peak?

Reply 526

Kaya22

Original post by Hadigy

why?

Reply 527

Jpw1097

Original post by Kaya22

oh well if its weak base it wont come up as that isnt on the spec at all so i wouldn't worry about kb

Exactly.

Reply 528

SophieAS

Hey, sorry if it's already been mentioned I just skipped to the end. Does anyone know where I can find the WJEC CH4 and CH5 threads if there are some??

Reply 529

Ebaysass

Original post by Hadigy

what's the M+4 peak??

Reply 530

Anon_98

Original post by Ultracrepidarian

legend, will you be doing the same for unit5?

Yes, planning to but I've got quite a few exams next week so I'm worried I won't be able to fit it in.

Reply 531

Hatiki99

Original post by Ebaysass

what's the M+4 peak??

I found it in the cgp book, it is just when you have 2 x +2 isotopes such as 2 x br81 bonded to the same compound.

Reply 532

Ebaysass

Original post by Hadigy

I found it in the cgp book, it is just when you have 2 x +2 isotopes such as 2 x br81 bonded to the same compound.

oh ok, what page was that??

Reply 533

Hatiki99

Original post by Ebaysass

oh ok, what page was that??

Page 123

Reply 534

confusedkid1997

what is the general rule for the following reagents, as in when are suitable reagents?

1. Sn/HCl 2. LiAlH4 2. NaBH4

Reply 535

Ultracrepidarian

Original post by Anon_98

Yes, planning to but I've got quite a few exams next week so I'm worried I won't be able to fit it in.

i see, in any case good luck.

Reply 536

Kaya22

Original post by confusedkid1997

what is the general rule for the following reagents, as in when are suitable reagents?

1. Sn/HCl 2. LiAlH4 2. NaBH4

h2/ni for everything pretty much (its easiest to remember)

Reply 537

thehollowcrown

Original post by confusedkid1997

what is the general rule for the following reagents, as in when are suitable reagents?

1. Sn/HCl 2. LiAlH4 2. NaBH4

Sn/HCl used for reducing nitrobenzene to aromatic amines
LiAlH4 used for reducing nitriles to amines
NaBH4 is only strong enough to reduce ketones and aldehydes to alcohols

Reply 538

Ebaysass

Original post by Hadigy

Page 123

I get that the M+4 peak means there are 2 atoms of the halogen instead of one, but how does it change the ratio of the M and M+2 peak?? Do you thinkwe need to know that?