Edexcel A2 Chemistry Unit 4 26/01/12 PM

Original post by Sailingslipelick

I love you so much :dancing:

apart from the hydrogen bonding joke, hows your ucas going?

Reply 41

I got an A on jan 10 mock i just did

:woo:

so how's everyone's revison going?

Reply 42

NutterFrutter

OP

Original post by This Honest

I got an A on jan 10 mock i just did

:woo:

so how's everyone's revison going?

Nice.

Revision is going well. :smile:

Reply 43

Original post by NutterFrutter

Nice.

Revision is going well. :smile:

Nice to know!

When they talk about strong acid and weak acid dilution by 10 100 1000, do you understand it. The cgp book doesn't explain it well. :s-smilie:

I've lost my textbook in my room somewhere, so i can't look it up :mad:

Reply 44

NutterFrutter

OP

Original post by This Honest

Nice to know!

When they talk about strong acid and weak acid dilution by 10 100 1000, do you understand it. The cgp book doesn't explain it well. :s-smilie:

I've lost my textbook in my room somewhere, so i can't look it up :mad:

The CGP book explains that perfectly. :wink:

It's all to do with the maths.

Stong acid: [H+] = [Acid] and for weak acid: [H+] = sqrt(Ka*[Acid]). Then it's just a case of putting in different values for [Acid] each decreasing by a factor of 10, so 1, 0.1, 0.01. For a stong acid pH increases by 1, for a weak acid pH increases by 0.5.

Reply 45

Alright then.

The mock i just did had a question about dilutions:

"In the case of hydrochloric acid, dilution by a factor of 10 increases the pH by one unit. Suggest why the ethanoic acid behaves differently"

How would you go about doing this.

I got 0 for this :s-smilie:

Reply 46

Original post by NutterFrutter

The CGP book explains that perfectly. :wink:

It's all to do with the maths.

Stong acid: [H+] = [Acid] and for weak acid: [H+] = sqrt(Ka*[Acid]). Then it's just a case of putting in different values for [Acid] each decreasing by a factor of 10, so 1, 0.1, 0.01. For a stong acid pH increases by 1, for a weak acid pH increases by 0.5.

i forgot to quote you :colondollar:

please look above

Reply 47

NutterFrutter

OP

Original post by This Honest

Alright then.

The mock i just did had a question about dilutions:

"In the case of hydrochloric acid, dilution by a factor of 10 increases the pH by one unit. Suggest why the ethanoic acid behaves differently"

How would you go about doing this.

I got 0 for this :s-smilie:

It's the exact information I just gave. HCl is a strong acid, ethanoic acid is a weak acid. For HCl [H+] = [Acid] applies, so you could put in 1, 0.1 and 0.01 for [acid] which is the same for [H+], then work out pH = -log[H+], you should see it increase by 1 each time.

For Ethanoic acid [H+] = sqrt(Ka*[Acid]) applies. So, you need to know the value for Ka (this is either given or you can find it in the data booklet). Again, you just put in 1, 0.1 and 0.01 for [acid] and you will get values for [H+] then just work out pH again and each time it will increase by 0.5.

Reply 48

Sailingslipelick

1

Original post by James A

apart from the hydrogen bonding joke, hows your ucas going?

Not bad. I have an offer from King's, so I am happy that I will be going to university next year! Good luck with your interviews at Reading and UEA (looked at sig!), I'm sure you'll get into them. :^_^:

Which uni is your first choice?

Reply 49

Original post by Sailingslipelick

Not bad. I have an offer from King's, so I am happy that I will be going to university next year! Good luck with your interviews at Reading and UEA (looked at sig!), I'm sure you'll get into them. :^_^:

Which uni is your first choice?

sweeet, a girl in the year above who came from my school got into kings for medicine xD

Tough question really, it's a battle between bath, nottingham and UEA. right now, i would wanna go UEA (because i already went there for a biology trip and loved the campus :colone:

. uea have the best student satisfaction from all universities and the joint best school of pharmacy (with nottingham)

but ill have to wait and see when i get my interviews at notts and bath to see if i like the school of pharmacy. but going to bath would be nice, Sunday Times University of the Year award xD

again, best of luck with the rest of your application :smile:

Reply 50

Original post by NutterFrutter

It's the exact information I just gave. HCl is a strong acid, ethanoic acid is a weak acid. For HCl [H+] = [Acid] applies, so you could put in 1, 0.1 and 0.01 for [acid] which is the same for [H+], then work out pH = -log[H+], you should see it increase by 1 each time.

For Ethanoic acid [H+] = sqrt(Ka*[Acid]) applies. So, you need to know the value for Ka (this is either given or you can find it in the data booklet). Again, you just put in 1, 0.1 and 0.01 for [acid] and you will get values for [H+] then just work out pH again and each time it will increase by 0.5.

thanks man :yeah:

Reply 51

Chaofan88

10

Aaah, revision is going okay but in practice I'm terrible. Pretty sure I scored an E/D in my last mock paper :s-smilie:

I need to get an A as well to fufill my Oxford offer :'( How do you guys revise?

Reply 52

Jukeboxing

8

I'm still going through the syllabus, currently on Carbonyl Compounds. I'm not going to attempt any past papers until i've gone over everything.

Reply 53

Toshiya

1

Done a couple of past papers, got one A and one C. It seems I struggle at some things a lot and am absolutely fine with others. I think I'll be okay, I'm more worried about physics unit 4 and C3 which I have in the same week.
I've done a reasonable amount of work so far but now xmas is over it's time to start the real work >_>

Reply 54

EffKayy

16

Original post by This Honest

Nice to know!

When they talk about strong acid and weak acid dilution by 10 100 1000, do you understand it. The cgp book doesn't explain it well. :s-smilie:

I've lost my textbook in my room somewhere, so i can't look it up :mad:

How I remember when something is diluted , the hydrogen concentration is removed, so diluting by 10 means dividing by 10 for the h+.

Congrats on the A btw.
The paper I liked out of them all was the jan2011 paper!

Reply 55

i think i have just about mastered acid/base/buffer questions.

do you guys know if the half neutralisation point of titration curves is in the syllabus?? because it's in the george facer book.

the only concern i have is rates of equations when they ask for why a particular reactant is in excess!

i got all the organic chemistry under control so im looking for a solid A on this paper to meet my predicted grade.

Reply 56

Original post by James A

i think i have just about mastered acid/base/buffer questions.

do you guys know if the half neutralisation point of titration curves is in the syllabus?? because it's in the george facer book.

the only concern i have is rates of equations when they ask for why a particular reactant is in excess!

i got all the organic chemistry under control so im looking for a solid A on this paper to meet my predicted grade.

a particular reactant can be in excess so that it will not have an effect on the rate/order of reaction

Reply 57

Original post by EffKayy

How I remember when something is diluted , the hydrogen concentration is removed, so diluting by 10 means dividing by 10 for the h+.

Congrats on the A btw.
The paper I liked out of them all was the jan2011 paper!

nice method, thanks :biggrin:

Need to replicate that A for the real exam :colone:

I'm going to do the jan 11 tomorrow :crossedf:

so by then, i would have done all past papers :woo:

was jan 11 relatively easier than the others?

Reply 58