OCR B Salters - F335 Exam - 15 June 2011

I'm good now with all of the Kw, Ka, Kg, Klol etc calculations. However I'm still struggling to get buffers. I understand that they maintain a constant pH with the addition of acid or Alkali, but I'm struggling to see how.

Some reasons why I'm confused.

|Does every buffer contain a Weak Acid/Conjugate Acid AND a Weak Base/Conjugate Base working together?

They contain one of those sets.

Reply 361

Conor 419

What decides why I'd use one set over the other?

(edited 12 years ago)

Reply 362

zahre

Original post by Conor 419

I'm good now with all of the Kw, Ka, Kg, Klol etc calculations. However I'm still struggling to get buffers. I understand that they maintain a constant pH with the addition of acid or Alkali, but I'm struggling to see how.

Some reasons why I'm confused.

|Does every buffer contain a Weak Acid/Conjugate Acid AND a Weak Base/Conjugate Base working together?

A buffer solution consists of a weak acid and one of its salts(e.g ethanoic acid and sodium ethanoate) OR a weak base and one of is salts (e.g ammonia and ammonium chloride). The acid partially dissociates into H+ ions and the salt dissociates completely.

Reply 363

beckyxo

in these exams they seem to refer to a buffer as a mixture of the acid and its salt.
some past paper i did asked this about ammonia, so a buffer solution of ammonia would be ammonia solution with ammonium nitrate, for example

Reply 364

Conor 419

Why would I use one over the other?

Reply 365

beckyxo

to bed!!
wish i could do an all nighter and crack out this exam, but i cant do two all nighters in a row. (english exam on thurs morn)
what freak does chemistry and english? oh yeah, me..
theres me and one other person i think who do both. why why why did i think it would be a good idea :frown:

Reply 366

cORBO3

Does anyone have the Jan 2011 paper and markscheme thanks!

Reply 367

Jamesrb

Original post by cORBO3

Does anyone have the Jan 2011 paper and markscheme thanks!

Search on the forum or in this thread, it's all over the place :smile:

Reply 368

Conor 419

Original post by beckyxo

to bed!!
wish i could do an all nighter and crack out this exam, but i cant do two all nighters in a row. (english exam on thurs morn)
what freak does chemistry and english? oh yeah, me..
theres me and one other person i think who do both. why why why did i think it would be a good idea :frown:

I do both ;D

Reply 369

joestevens2092

3

Think I'm pretty much sussed for this exam, might give everything a once over before the exam but apart from that I'm done! Good luck guys

Reply 370

TheDustyKid

15

Revision was going well but, somehow, i'm watching Tales of Mere Existence now...

Reply 371

parallal

I don't know if this question has been asked already (sorry if it has) but do we need to know a labelled diagram for the apparatus for reflux?

Reply 372

Adam9

Original post by Tetanus

you sure?

Im sure ... its in my revision guide, and i have just checked it again . definitely

Reply 373

AGM

10

Original post by parallal

I don't know if this question has been asked already (sorry if it has) but do we need to know a labelled diagram for the apparatus for reflux?

I doubt it, they could bring it up I guess as it is synoptic... but that's past units really.

If they do it's just, pear shape flask, anti-bumping granules, open top, flame, condenser

Reply 374

Adam9

any1 got june 2010 paper ????????????? or know where to find it

Reply 375

parallal

Original post by AGM

I doubt it, they could bring it up I guess as it is synoptic... but that's past units really.

If they do it's just, pear shape flask, anti-bumping granules, open top, flame, condenser