The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

Moles

Can someone help me with Q10(d), I don't understand why we divide moles NaOH by 3, I though you would divide moles of the carboxylic acid by 3??? I always get confused with handling moles like these
http://filestore.aqa.org.uk/subjects/AQA-CHM6X-QP-JUN12.PDF
Reply 1
Avatar for Metanoia
Metanoia
9
Original post by ps1265A
Can someone help me with Q10(d), I don't understand why we divide moles NaOH by 3, I though you would divide moles of the carboxylic acid by 3??? I always get confused with handling moles like these
http://filestore.aqa.org.uk/subjects/AQA-CHM6X-QP-JUN12.PDF


I'm not sure of the context of your statement highlighted in red.

But the calculations along the way should involve
moles of carboxylic acid = (moles of NaOH/3)
Reply 2
Avatar for ps1265A
ps1265A
OP
14
Original post by Metanoia
I'm not sure of the context of your statement highlighted in red.

But the calculations along the way should involve
moles of carboxylic acid = (moles of NaOH/3)


Could you explain why we divide NaOH by 3, and not the carboxylic acid?
Reply 3
Avatar for Metanoia
Metanoia
9
I think I should edit my first post.

There are a maximum of 3 acidic groups COOH that could be created from the complete hydrolysis of each molecule of fat.

Working backwards

moles of NaOH = moles of COOH

moles of fat hydrolyzed = (moles of COOH)/3 or (moles of NaOH)/3
(edited 8 years ago)
Reply 4
Avatar for ps1265A
ps1265A
OP
14
Original post by Metanoia
I think I should edit my first post.

There are a maximum of 3 acidic groups COOH that could be created from the complete hydrolysis of each molecule of fat.

Working backwards

moles of NaOH = moles of COOH

moles of fat hydrolyzed = (moles of COOH)/3 or (moles of NaOH)/3


I did do COOH/3 but I keep getting a different answer


Posted from TSR Mobile
Reply 5
Avatar for Metanoia
Metanoia
9
Try posting your answers here.
Reply 6
Avatar for ps1265A
ps1265A
OP
14
Original post by Metanoia
Try posting your answers here.


I understand it now!

I have one ore question regarding moles... Q3... http://www.a-levelchemistry.co.uk/AQA%20A2%20Chemistry/Unit%206/ISA%20(EMPA)/AQA-CHM6X-W-SQP-07.pdf

I understand the concept gmol-1 x moldm-3 = gdm-3

But what data do I use in the introduction?
Reply 7
Avatar for Pigster
Pigster
20
You know how many mol of Y there are in the titre.

You know that you used 1/10th of the standard solution you made up, so you know how many mol there were in the 250 cm3 standard solution.

Since you know that there is 1.419 g of carboxylic acid and you know how many mol that is, it is a simple calculation to work out its Mr.
Reply 8
Avatar for ps1265A
ps1265A
OP
14
Original post by Pigster
You know how many mol of Y there are in the titre.

You know that you used 1/10th of the standard solution you made up, so you know how many mol there were in the 250 cm3 standard solution.

Since you know that there is 1.419 g of carboxylic acid and you know how many mol that is, it is a simple calculation to work out its Mr.


But we're working out concentration???
Reply 9
Avatar for Pigster
Pigster
20
Q1 - you work out the ave. titre of alkali.

From that you can work out how many mol. of NaOH.

Since all the carboxylic acids are monobasic acids i.e. 1 mol of acid releases 1 mol of H+.

Therefore the amount of acid is equal to the amount of alkali.

Which is in 25 cm3... calc me do.

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you