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Buffer question

Edit: attached the question as it didn't post properly!


Please can someone explain this question?

Answer is Z as there's move salicylic acid than OH-

Mark scheme says the 'idea that solution contains both HA and A-



But the OH- isn't A-...is it? A little confused as to why it's Z!
(edited 6 years ago)
Original post by jazz_xox_
Edit: attached the question as it didn't post properly!


Please can someone explain this question?

Answer is Z as there's move salicylic acid than OH-

Mark scheme says the 'idea that solution contains both HA and A-



But the OH- isn't A-...is it? A little confused as to why it's Z!


you may need to edit this post again ...
Reply 2
Avatar for jazz_xox_
jazz_xox_
OP
13
Original post by charco
you may need to edit this post again ...


Oops, thanks for letting me know! I'll try and attach it here as it's not wanting to go in the OP for some reason ://
buffer.png86.7KB
Ok its an example of a neutralisation buffer, where HA and NaOH both react to produce their own salt (NaA is the salt same as saying A-) and water. So the buffer is only made after the reaction of HA and NaOH.
Equation is HA + NaOH → NaA + H2O.
All the A- (NaA) in the solution will come from HA, so there needs to be an excess of HA (75cm3) and less NaOH.
The moles of OH- are the same as A- only because NaOH is the limiting reagent so determine how much NaA is produced. 😊
Reply 4
Avatar for jazz_xox_
jazz_xox_
OP
13
Original post by makami11
Ok its an example of a neutralisation buffer, where HA and NaOH both react to produce their own salt (NaA is the salt same as saying A-) and water. So the buffer is only made after the reaction of HA and NaOH.
Equation is HA + NaOH → NaA + H2O.
All the A- (NaA) in the solution will come from HA, so there needs to be an excess of HA (75cm3) and less NaOH.
The moles of OH- are the same as A- only because NaOH is the limiting reagent so determine how much NaA is produced. 😊


Thank you! So is the aim of a neutralisation buffer to obtain a solution of a weak acid and it's salt (once the acid has reacted)?
So it would act as an acidic buffer, meaning HA needs to be in excess so it all doesn't react?

Do you think they would ever give an example like this with a weak base and its salt? So reacting excess of weak base with strong acid?
Thanks again :smile:
Original post by jazz_xox_
Thank you! So is the aim of a neutralisation buffer to obtain a solution of a weak acid and it's salt (once the acid has reacted)?
So it would act as an acidic buffer, meaning HA needs to be in excess so it all doesn't react?

Do you think they would ever give an example like this with a weak base and its salt? So reacting excess of weak base with strong acid?
Thanks again :smile:


Yeh thats the aim but without having to directly add the salt in the beginning. Im not sure what exam board you're doing, weak base is not needed on my spec AQA. Hope that helped!
Reply 6
Avatar for jazz_xox_
jazz_xox_
OP
13
Original post by makami11
Yeh thats the aim but without having to directly add the salt in the beginning. Im not sure what exam board you're doing, weak base is not needed on my spec AQA. Hope that helped!


Oh good, I'm AQA too! Thank you :smile:

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