OCR Salters Chemistry F335 12th June 2013 Exam revision thread

Original post by tsr1

for june 2012 question 5e)

the last mark in the mark scheme is for saying 'Entropy loss of water/more order in water'

does anyone one know what it means.. I am not sure how to put it in a sentence that make sense? thanks

In entropy in water decreases so there is less disorder

Reply 205

tsr1

Original post by super121

In entropy in water decreases so there is less disorder

so in solid, there is no water and therefore, there is low entropy?

(edited 10 years ago)

Reply 206

Original post by tsr1

so in solid, there is no water and therefore, there is low entropy?

I don't know what the question is, but entropy decreases going from a liquid to a solid
Gases have the most entropy while solids have the least :smile:

Reply 207

tsr1

Original post by super121

I don't know what the question is, but entropy decreases going from a liquid to a solid
Gases have the most entropy while solids have the least :smile:

salts consists of small highly charged ions e.g. ca+2, S(sys) has a negative value

suggest why S(sys) is often more positive for dissolving processes but negative for the dissolving of some calcium salts

so, the last mark was for saying 'entropy loss of water / more order in water ' which I was confused about...

Reply 208

Original post by tsr1

salts consists of small highly charged ions e.g. ca+2, S(sys) has a negative value

suggest why S(sys) is often more positive for dissolving processes but negative for the dissolving of some calcium salts

so, the last mark was for saying 'entropy loss of water / more order in water ' which I was confused about...

It's just saying that there is less entropy in water, because in the question we were told that Ca ions have a negative values for deltaSsys, suggesting that entropy decreases.
Remember, if deltaSsys is negative, entropy decreases and vice versa

Reply 209

Ikklemini

6

Original post by Ikklemini

I'm doing the jan 2011 paper and not sure about question 4) (f)

It says explain what is meant by a buffer solution and how a buffer solution works by referring to the equilibrium in equation 4.1.

resists pH change AW 
when acid/alkali added 
in small quantities 
equilibrium moves to left when acid added [ORA for alkali] 
removing acid / H+ [ORA for alkali]  large concentration of HCO3– 

The mark scheme had this answer but I dont understand the change in equlibrium- could someone explain this please!! Thank you x

Can someone please help with this question ?

Posted from TSR Mobile

Reply 210

Original post by Ikklemini

Can someone please help with this question ?

Posted from TSR Mobile

It moves to the left to counteract the change of the acid being added, because there's a higher conc of acid on the right

Reply 211

martynsteel

11

Original post by Jlane5000

Hi, sorry if i'm being really stupid but could you walk me through how you got the answer. I've been trying to figure it out for an hour. I thought to work out the conc of H+ that it was ka * [HA]/[A-]

but in your calculation you have the salt being divided by the acid, and i'm confused why. Sorry if i'm being thick, i've been staring at it too long and my brain has turned to mush :colondollar:

If you look in Chemical Ideas on Page 191 the equation I'm using in under the text saying "If we make use of assumptions 1 and 2 above" :smile:

Reply 212

martynsteel

11

Original post by Tikara

Guysss can I get some help with nmr spectroscopy? The mark scheme says neither of the peaks have splitting :frown:

Can you not have splitting when the H is bonded to an O ? or when there is in O next to the C?

You don't get splitting through oxygen's due to their high electronegativity :-) (If I remember correctly)

Edit: You don't get splitting because the environments are separated by an oxygen, an oxygen is more likely to shift a peak downfield due to electronegativity

(edited 10 years ago)

Reply 213

Salmonidae

1

Hey team,

Just to clarify, the conditions for hydrolysis of an ester and an amide are the same right? Dilute HCL/NaOH and reflux?

Cheers

Reply 214

suncake

14

Original post by Salmonidae

Hey team,

Just to clarify, the conditions for hydrolysis of an ester and an amide are the same right? Dilute HCL/NaOH and reflux?

Cheers

Yep

Reply 215

abzy1234

14

Original post by Salmonidae

Hey team,

Just to clarify, the conditions for hydrolysis of an ester and an amide are the same right? Dilute HCL/NaOH and reflux?

Cheers

I would love to say it is, but the mark schemes differ so widely! One time it says, ignore dilute and only accept mod. concentrated, other times it says the polar opposite! :/

I would, though, still write what you said; it's what the books say, so you can't go wrong tbh save crazy OCR markers :smile:

Reply 216

suncake

14

Original post by abzy1234

I would love to say it is, but the mark schemes differ so widely! One time it says, ignore dilute and only accept mod. concentrated, other times it says the polar opposite! :/

I would, though, still write what you said; it's what the books say, so you can't go wrong tbh save crazy OCR markers :smile:

Haha really? Where on earth does it say moderately concentrated anywhere in the textbooks?! Gah, I hate overly picky mark schemes :tongue:

Reply 217

Salmonidae

1

Original post by abzy1234

I would love to say it is, but the mark schemes differ so widely! One time it says, ignore dilute and only accept mod. concentrated, other times it says the polar opposite! :/

I would, though, still write what you said; it's what the books say, so you can't go wrong tbh save crazy OCR markers :smile:

Original post by suncake

Haha really? Where on earth does it say moderately concentrated anywhere in the textbooks?! Gah, I hate overly picky mark schemes :tongue: