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Buffer solution help

A CH3COOH/CH3COONa buffer containing 01M CH3COOH has pH of 4.742
(a) Determine conc of CH3COONa in this solution
what should I use in this question?

Reply 1

B_9710

Wouldn't you need the Ka value of CH3COOH ?

Reply 2

Pigster

You also need to know the Ka or pKa for ethanoic acid, which I'll bet is somewhere in the Q and you just haven't typed it. I'm also guessing that that is a 0.1 mol dm-3 solution, rather than 01 mol dm-3.

You're going to use the expression for Ka and one of the two that relates [H+] with pH.

How do you think you might start?

I'm also guessing that you're either American or have a pretty old teacher.

Reply 3

B_9710

You can immediately work out the [H+] as you have the pH. Then using the Ka and concentration of the acid you can rearrange the formula for Ka to find the concentration of CH3COONa.

Reply 4

alavisteam

Unit 4 chemistry January 2016 buffer question?? I sat for it
Mine was 3.09 what was yours???

Reply 5

Sandy_Vega30

Original post by alavisteam

Unit 4 chemistry January 2016 buffer question?? I sat for it
Mine was 3.09 what was yours???

Mine was 0.602.. i had no had what to do after obtaining the moles in equilibrium. It was out of 5 marks and i hope i get at least 3 marks for calculating the moles at start and at equilibrium. How was Section C for u?

Reply 6

alavisteam

Section ç was easy
Overall i found the paper somewhat easy
expecting above 108 In Sha Allah
What about you??

Original post by Sandy_Vega30

Reply 7

melanin101

K_a = [H⁺][Salt] / [Acid]

You need to rerrange the above to find out the concentration of the salt. You can find the concentration of H⁺by antilogging the pH: [H⁺] = 10^(-pH)

You'll find these equations useful:

CH₃COOH <--> CH₃COO^-+ H⁺
_{High amount of CH₃COOH}

CH₃COONa --> CH₃COO^-+ Na⁺
^{High amount of}^CH₃^COO^-

(edited 8 years ago)

Reply 8

alis722

what i did was Ka=Buffer/[H][OH] and got a pH of 6.8

Reply 9

mdfaiz99

What about the last question ? Was it an ester? And how many peaks was it in the NMR?

Reply 10

B_9710

What was the Ka value you were given?

Reply 11

jackien1

Original post by mdfaiz99

What about the last question ? Was it an ester? And how many peaks was it in the NMR?

Ester, 2 peaks, both singlets. Peak ratio 3:9

Reply 12

Sandy_Vega30

Original post by alavisteam

Section ç was easy
Overall i found the paper somewhat easy
expecting above 108 In Sha Allah
What about you??

I didnt dind section C easy,.. i had little time to attempt it. What the heck was Z compound? I hope for an A. In Shah Allah. :smile:

Reply 13

Sandy_Vega30

Original post by jackien1

Ester, 2 peaks, both singlets. Peak ratio 3:9

What was the structure of the ester?

Reply 14

shady2.0

Ohhh thank you so much ....Melanin....from all people u have shown me the easiest and more understandable way Thank you again

Reply 15

shady2.0

So does is it mean that [CH3COONA] = [CH3COO-]?

Reply 16

melanin101

Original post by shady2.0

So does is it mean that [CH3COONA] = [CH3COO-]?

Yes, as the salt CH₃COONa, disassociates fully in solution.

Reply 17

mdfaiz99

Original post by Sandy_Vega30

What was the structure of the ester?

CH3COOC(CH3)3 I think it was Butylethanoate ( Tertiary alcohol with ethanoic acid)

Reply 18

ajsullivan

I have attached a worked answer for this question. I hope this helps, and you could always check out my website www.scienceskool.co.uk for more help! :smile:

Have fun.

Alex

Answer Small.jpg