Chemistry unit 4 AQA

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Reply 480

Chuck1993

Could anyone explain how base hydrolysis of esters works? The NT book is really confusing.

Reply 481

The_ditto

For geometrical isomers, should there always be two of the same groups attached to one of the carbons

Reply 482

bwfcboy93

Original post by Chuck1993

Could anyone explain how base hydrolysis of esters works? The NT book is really confusing.

With H20 and an Acid Catalyst such as HCl Esters break down into constituent Alcohols and Carboxylic acids

With H20 and Basic catalyst - such as NaOH - Esters break down to form an alcohol and a sodium salt - e.g. CH3CH2COONa - These sodium salts can be used as soaps

Hope that helps :smile:

Reply 483

Chuck1993

Original post by bwfcboy93

Thank you!

Reply 484

JesusIsMyHomeboy

Having a mental block and can't do this question:

Calculate the pH of the solution formed when 10.0cm3 of 0.154mol dm-3 hydrochloric acid are added to 990cm3 of water.

Apparently the answer is pH=2.81. How do you get that? In question above, i got pH of hydrochloric acid is 0.81 if that's relevant.

Probably a really simple question but I can't get my head around it :/

Reply 485

username872714

can ketones form hydrogen bonds between molecules? or not? :s

Reply 486

al_habib

Original post by Chuck1993

Could anyone explain how base hydrolysis of esters works? The NT book is really confusing.

when you hydrolyse ester you are breaking ester bond or ester linkage using NaoH to form carboxylic acid and alcohol

Reply 487

Besakt

Original post by JesusIsMyHomeboy

M1 x V1 = M2 x V2

0.154 x 10 = M2 x (total volume which is 990cm3 + 10 cm3 = 1000cm3)

then you do (0.154 x 10)/1000

Which gives M2 to be 1.54 x10-3 so [H+] = 1.54 x10-3

then you just -log it to find ph

Reply 488

Alpha5

I feel so nervous about this exam. Do we have to know 2 step titration curves, for instance the reaction between Na2CO3 and H2SO4, it's on the old spec but I don't think we do? Thanks

Reply 489

al_habib

Original post by sarah-madeline

can ketones form hydrogen bonds between molecules? or not? :s

yes they can coz they got c=o where oxygen from carbonyl forms hydrogen bond with hydrogen from water see page 67 nelson thornes book top right

Reply 490

JesusIsMyHomeboy

Original post by Besakt

Cheers! Out of rep, sorry :frown:

I feel like I've been quoted my TSR Royalty :tongue:

Thanks again

Reply 491

poison.

Original post by sarah-madeline

can ketones form hydrogen bonds between molecules? or not? :s

erm i think my textbook says dipole-dipole (ie permanant delta - charges on the O, and delta + charges on the C) and that this expains why they have a lower boiling/melting point to alcohols of a similar Mr, because alcohols do have hydrogen bonding. i think the O (or similarly electronegative atom) would have to be directly bonded to the H, for hydrogen bonding :smile:

edit: please feel free to rectify me if i'm wrong - i'm no chemistry wizz!

Reply 492

Alpha5

Original post by sarah-madeline

can ketones form hydrogen bonds between molecules? or not? :s

They can form hydrogen bonds with water, but not between alike molecules. It's more likely to have dipole-dipole interactions.

Reply 493

eesha_25

I'm probably being really dumb but 4ai on June 2011 paper...isn't propanedioic acid HOOCCH2COOH?

Reply 494

al_habib

Original post by Alpha5

I feel so nervous about this exam. Do we have to know 2 step titration curves, for instance the reaction between Na2CO3 and H2SO4, it's on the old spec but I don't think we do? Thanks

i'll say learn the calculation bit who knows they might bring that as they did in one of 2004 paper i think and learn half neutralisation as well where ph=pKa