Chemistry unit 4 AQA

Reply 260

Legendary

1

Anyone else at the point where you've done everything and there's nothing left to do?

Reply 261

thomas93

Original post by nasira372

How can you tell if the acid/base is weak or strong?

Also, how are we supposed to know what the salts of the weak acids/bases are?

The acids: if it is not a common acid (one which you'd know whether it was strong or weak) then it will say in the question.

Any salt of A- will suffice.

Reply 262

rommy123

Original post by thomas93

I do, I do. That is for my 5 (now 4) exams though. And It's only because I genuinely enjoy the subjects, so I don't find it too painful.
I love organic, but only because the teacher I had for it was f*cking amazing! I know a lot of people really hate it, it must be like marmite. :P

you got any tips to revise organic?
especially N.M.R and carbon 13 spec

Reply 263

thomas93

Original post by rommy123

http://www.mediafire.com/?r74x3pdjrhay7

^^^^ this might help you, you`ll have to download it, the notes are really good

They're actually awesome!

Reply 264

rommy123

Original post by thomas93

They're actually awesome!

yup they are :smile:

Reply 265

thomas93

Original post by rommy123

you got any tips to revise organic?
especially N.M.R and carbon 13 spec

Hmm, I think with those kind of topics practice makes perfect, because there isn't much knowledge on them, it's more the application of the knowledge. Just practice the, find as many NMR questions as you can and do them, over and over again if needs must.
Obviously make sure you're comfortable with the knowledge before you do that. And make sure you know the solvents and standard compounds, they're easy marks.

I know, it's a bit vague, but i hope that helps a little. :colondollar:

Reply 266

rommy123

Original post by thomas93

Hmm, I think with those kind of topics practice makes perfect, because there isn't much knowledge on them, it's more the application of the knowledge. Just practice the, find as many NMR questions as you can and do them, over and over again if needs must.
Obviously make sure you're comfortable with the knowledge before you do that. And make sure you know the solvents and standard compounds, they're easy marks.

I know, it's a bit vague, but i hope that helps a little. :colondollar:

yup its all about practicing :smile:

and thanks

Reply 267

amazingacademic

In naming compounds, do you need to know how to name phenyl alcohols?
or it limited to nitrobenzene, phenyl amine, phenyl ketones, phenylammonium salts?

Reply 268

Nuss

12

For making an alcohol via esterification, what are the conditions required?

Reply 269

thomas93

Original post by Nuss

For making an alcohol via esterification, what are the conditions required?

Hydrolysis? Just a strong acid catalyst... It's an equilibrium reaction...

Reply 270

Nuss

12

Original post by thomas93

Hydrolysis? Just a strong acid catalyst... It's an equilibrium reaction...

Are you meant to put reflux as one of the conditions? Saw a mark for it in one of the old past papers, but it was for making the ester as opposed to making an alcohol

(edited 12 years ago)

Reply 271

Accalia

12

Original post by tgarrud

83/100 raw marks

The ums boundaries do not change; thats the whole point in them being scaled.

Ah, sorry

I've been working from some of the older past papers, pre-syllabus change. They're only out of 90.

Reply 272

Accalia

12

Original post by Nuss

For making an alcohol via esterification, what are the conditions required?

Do you mean making an alcohol from an ester, or using an alcohol to form an ester? Conditions for esterification differ depending on what your using with the alcohol (acid chlorides react vigorously, so they can be used at room temperature; acid anhydrides less so, heat will be needed; carboxylic acids will require a sulphuric acid catalyst).

But if you want to get the alcohol from an ester, then you can go either base or acid catalysed hydrolysis. I think it's reflux for both of these (haven't yet seen a markscheme penalising 'reflux' so it doesn't hurt to add it on). Base-catalysed hydrolysis is also referred to as saponification (the salt you get can be made into soap).

(edited 12 years ago)

Reply 273

liviaaa

How much do we need to know about Chromatography? We have literally learnt about the moving/stationary phases and that it can be used to separate amino acids. Do we need to know about Rf values or anything like that? :s-smilie:

Reply 274

Besakt

3

Original post by liviaaa

How much do we need to know about Chromatography? We have literally learnt about the moving/stationary phases and that it can be used to separate amino acids. Do we need to know about Rf values or anything like that? :s-smilie:

Know that separation by column chromatography depends
on the balance between solubility in the moving phase and
retention in the stationary phase.

Know that gas-liquid chromatography can be used to
separate mixtures of volatile liquid.

Reply 275

Erotas

Could somebody explain how to do 1aiv from the January 2011 paper please? Thanks :smile:

Reply 276

liviaaa

Original post by Erotas

Could somebody explain how to do 1aiv from the January 2011 paper please? Thanks :smile:

You half each of the conc. in the rate equation (as water doubles the volume, so the conc of each halves), but k stays constant.

Reply 277

Erotas

Original post by liviaaa

You half each of the conc. in the rate equation (as water doubles the volume, so the conc of each halves), but k stays constant.

Ohh right, that makes sense :tongue:

thank you.

Reply 278

JesusIsMyHomeboy

9

Can someone help me with naming of amino acids? There was a question on JUN 11, but I don't have the paper on me to know which question number it as.

Reply 279

Besakt

3

Original post by JesusIsMyHomeboy

Can someone help me with naming of amino acids? There was a question on JUN 11, but I don't have the paper on me to know which question number it as.

That is glycine. IUPAC name is 2-aminoethanoic acid.

Amino acid always has a carboxylic acid group at the end so will always end with ...oic acid

They also always have an amino group so will always start with x-amino....(the x is the number on the carbon where the amino group is).

Then it is just a matter of finding the shortest chain.

Chemistry unit 4 AQA

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