Edexcel A2 Chemistry Unit 4 26/01/12 PM

Please can someone go through the trends in solubility for the group 2 sulfates and the group 2 hydroxides?! I'm getting it all confused. It will be much appreciated!

woah woah woah.........

woah

that's unit 2 mate. but it might be useful for this unit.

solubility increases in hydroxides down the group.
solubility decreases in sulfates down the group.

Reply 581

Shopaholic94

Original post by James A

woah woah woah.........

woah

that's unit 2 mate. but it might be useful for this unit.

solubility increases in hydroxides down the group.
solubility decreases in sulfates down the group.

No, I mean the part when you go on about enthalyp of hydration, lattice and all that. I'm so confused?!

Reply 582

.snowflake.

14

Original post by EffKayy

wtf this is unit 4 braaah

it comes up with all the dissolving stuff, deltaHsolution, lattice energy etc. and we use them to explain why the trends occur

Reply 583

Onee-chan

1

Original post by Sandeep G

yes defo

Original post by .snowflake.

Yes. It's in the revision guide.

What revision guide do we speak of?! It's not in the edexcel book (the "endorsed by edexcel" one)!

So we need to know the rings and stuff?! I vaguely remember my teacher saying that we didn't need to know it?

Reply 584

.snowflake.

14

Original post by Onee-chan

What revision guide do we speak of?! It's not in the edexcel book (the "endorsed by edexcel" one)!

So we need to know the rings and stuff?! I vaguely remember my teacher saying that we didn't need to know it?

the purple Edexcel little revision guide.

Reply 585

wam-bam

1

Original post by Onee-chan

What revision guide do we speak of?! It's not in the edexcel book (the "endorsed by edexcel" one)!

So we need to know the rings and stuff?! I vaguely remember my teacher saying that we didn't need to know it?

i don't think we do, but i want some-one else to confirm it ....... pleeeaasseee!!!!

Reply 586

EffKayy

16

We dont need to know about the structure

Reply 587

F1's Finest

21

Original post by EffKayy

We dont need to know about the structure

structure of?

Reply 588

wam-bam

1

Original post by James A

structure of?

we don't need to know the specific equation and structure of the reaction if brady's reagent with carbonyl compounds

Reply 589

F1's Finest

21

Original post by wam-bam

we don't need to know the specific equation and structure of the reaction if brady's reagent with carbonyl compounds

aha.

but what about the colour of the precipitate with the carbonyl group? we have to learn that definitely.

Reply 590

sceptic_medic

9

Original post by Sandeep G

yes defo

We really don't...

Reply 591

343arcou

5

Solubility is waste.....

what, if there is, is the relationship between delta-H-solution and delta-s-total
Like how do you find out total from solution (obviously need other data I know that) but is solution essentially the same as system so total = surroundings + solution

Or am I making this up?

Reply 592

ih8edexcel!

Original post by wam-bam

we don't need to know the specific equation and structure of the reaction if brady's reagent with carbonyl compounds

just knw tht ppt is orange

Reply 593

sceptic_medic

9

Guys and girls, I have a quick question on transesterification. It's used as an alternative to hydrogenation for solidifying vegetable oils because that produces trans isomers in the fatty acid chains. The textbook says however that methanol (or the desired alcohol) reacts with the ester to form a new ester and the glycerol. However this swaps the alcohol not the fatty acid chains! I'm very confused!

Reply 594

Parthenon93

7

Original post by marc_h94

Guys and girls, I have a quick question on transesterification. It's used as an alternative to hydrogenation for solidifying vegetable oils because that produces trans isomers in the fatty acid chains. The textbook says however that methanol (or the desired alcohol) reacts with the ester to form a new ester and the glycerol. However this swaps the alcohol not the fatty acid chains! I'm very confused!

There are two types of transesterification.

One type swaps the ester's acid part with another acid. This is done for margarine.

Another type swaps the ester's alcohol part with another alcohol. This is done for biofuel. I think the Edexcel endorsed book gives details of this reaction only, that is why you are confused. :redface:

Reply 595

sunnybacon

12

Original post by Sandeep G

What is the pH of a solution containing 45cm^3 of 0.1moldm^-3 NaOH and 25cm^3 of 0.15moldm^-3 HCl

OKAY it's strong acid with strong base so no constant involved other than Kw (1x10^-14)

Moles of NaOH = 45/1000 x 0.1 = 4.5x10^-3
Moles of HCl = 25/1000 x 0.15 = 3.75x10^-3
So as NaOH has more moles, it is in excess

But what do I do from here to work out the pH?

I'd guess you do moles of OH- minus moles of H+ to work out the OH- remaining that hasn't been neutralized.
So (4.5x10^-3)-(3.75x10^-3) = 0.75x10^-3
Then find this as a concentration...you know the total volume is 70cm3, I cba to do the calculation :biggrin:

Then use Kw to find [H+] because you know the value of Kw and [OH-] from the previous step.
Then you can use -log[H+] to get the pH :smile:

Reply 596

Revent

10

Original post by Sandeep G

What is the pH of a solution containing 45cm^3 of 0.1moldm^-3 NaOH and 25cm^3 of 0.15moldm^-3 HCl

OKAY it's strong acid with strong base so no constant involved other than Kw (1x10^-14)

Moles of NaOH = 45/1000 x 0.1 = 4.5x10^-3
Moles of HCl = 25/1000 x 0.15 = 3.75x10^-3
So as NaOH has more moles, it is in excess

But what do I do from here to work out the pH?

I THINK 14-log((4.5x10^-3-3.75x10^-3)/(70/1000))

(edited 12 years ago)

Reply 597

sceptic_medic

9

Original post by Parthenon93

There are two types of transesterification.

One type swaps the ester's acid part with another acid. This is done for margarine.

Another type swaps the ester's alcohol part with another alcohol. This is done for biofuel. I think the Edexcel endorsed book gives details of this reaction only, that is why you are confused. :redface:

Thank you very much! Yeah that's sorted it. Do you mind giving the reaction conditions for each, or do we not need to know that? Oh and for bio-diesel it's the methyl and ethyl esters which burn most efficiently so you add ethanol and methanol is that correct? :smile:

Reply 598

areyousure?

13

Hey guys

Any of you have the Get the Grade Revision Guide by Facer, if you do and you've have done the Practice Unit Test let me know how you found it please :smile:

thanks

Reply 599

343arcou

5

Original post by Sandeep G

What is the pH of a solution containing 45cm^3 of 0.1moldm^-3 NaOH and 25cm^3 of 0.15moldm^-3 HCl

OKAY it's strong acid with strong base so no constant involved other than Kw (1x10^-14)

Moles of NaOH = 45/1000 x 0.1 = 4.5x10^-3
Moles of HCl = 25/1000 x 0.15 = 3.75x10^-3
So as NaOH has more moles, it is in excess

But what do I do from here to work out the pH?

I got pH as 10.875 if this is right then your basically there mate :smile:

Edexcel A2 Chemistry Unit 4 26/01/12 PM

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you