how many moles of NaOH does aspirin react with?

some places say 1, others say 2.. others say 3.

I want a decent answer and sound like you know what you're on about... gimme a source, perhaps?

thanks

I may even give a replier a new gem :eek:

Reply 1

gyrase

3

Why do you want aspirin to react with NaOH? :confused:

NaOH is required in the synthesis of aspirin.

Reply 2

Saffie

OP

11

actually i need to know how many moles of salicylic acid react with NaOH too, if anyone can help?

I need to know to do the calculations of a titration between the two :smile:

It's seriously annoying that so many different sources say different amounts of moles react, but my results look like it's 1 mole to 1 mole.

Reply 3

oxymoron

7

Saffie

actually i need to know how many moles of salicylic acid react with NaOH too, if anyone can help?

I need to know to do the calculations of a titration between the two :smile:

It's seriously annoying that so many different sources say different amounts of moles react, but my results look like it's 1 mole to 1 mole.

Ignore that on 2nd thoughts!

I think one mole would react straight away with the acid group, then one mole would hydrolyse the ester and one mole would then react with the acid produced from the hydrolysis ... so overall 3 moles react.

Are you doing a back titration investigation? because if so, when you use the acid then all the excess NaOH will react but ALSO the phenoxide ion will gain a proton so effectively it will look as if only 2 moles of NaOH reacted.

Does that make sense?

Reply 4

Saffie

OP

11

Here are three equations I've found for it, the websites never seem to explain it, sorry.

CH3COO.C6H4.COOH + 3NaOH -> CH3COONa + NaO.C6H4.COONa + 2H2O

CH3COOC6H4COOH + 2NaOH -> CH3COONa + HOC6H4COONa + H2O

CH3COO.C6H4.COOH + NaOH -> CH3COO.C6H4.COONa + H2O

Reply 5

Saffie

OP

11

oxymoron

Ignore that on 2nd thoughts!

I think one mole would react straight away with the acid group, then one mole would hydrolyse the ester and one mole would then react with the acid produced from the hydrolysis ... so overall 3 moles react.

Are you doing a back titration investigation? because if so, when you use the acid then all the excess NaOH will react but ALSO the phenoxide ion will gain a proton so effectively it will look as if only 2 moles of NaOH reacted.

Does that make sense?

I'm doing both an acid/base titration and a back titration, so which equation for each experiment?

Thanks a lot, makes sense :biggrin:

edit: I gave you a shiny gem :proud:

Reply 6

oxymoron

7

Saffie

I'm doing both an acid/base titration and a back titration, so which equation for each experiment?

Thanks a lot, makes sense :biggrin:

edit: I gave you a shiny gem :proud:

Heh, thanks!

Back titration is definitely the 2nd equation overall assuming you use phenolphthalein as the indicator (ie high pH) as explained above.

For a simple acid/base titration I think it would just be 1 mole because the alkali hydrolysis wouldn't happen without heating and reflux and the NaOH added would just react quickly with the COOH group and then build up an excess after one mol/mol is added.

I think that's right!

Reply 7

Saffie

OP

11

bleh, what's the equation for salicylic acid and NaOH? Can't find it anywhere. :frown:

Reply 8

gyrase

3

Saffie

bleh, what's the equation for salicylic acid and NaOH? Can't find it anywhere. :frown:

C₆H₄(OH)COOH + NaOH --> C₆H₄(OH)COO^-Na⁺ + H₂O

Reply 9

Saffie

OP

11

Gnarl

C₆H₄(OH)COOH + NaOH --> C₆H₄(OH)COO^-Na⁺ + H₂O

cheers, you got a gem too :biggrin:

Reply 10

Saffie

OP

11

what's the equation for an equimolar mixture of salicylic acid and aspirin against NaOH?

Dya just kinda merge the equations? Such would be:

C6H4(OH)COOH + CH3COO.C6H4.COOH + 2NaOH --> C6H4(OH)COO-Na+ + CH3COO.C6H4.COONa + 2H2O

Reply 11

Saffie

OP

11

Saffie

what's the equation for an equimolar mixture of salicylic acid and aspirin against NaOH?

Dya just kinda merge the equations? Such would be:

C6H4(OH)COOH + CH3COO.C6H4.COOH + 2NaOH --> C6H4(OH)COO-Na+ + CH3COO.C6H4.COONa + 2H2O

is this right? I really need to know :blush:

Reply 12

oxymoron

7

Saffie

is this right? I really need to know :blush:

If just a simple acid/base titration then I would say yes. If heating under reflux then doing a back titration then you need to factor in the ester hydrolysis as above.

Reply 13

Saffie

OP

11

oxymoron

If just a simple acid/base titration then I would say yes. If heating under reflux then doing a back titration then you need to factor in the ester hydrolysis as above.