Help with finding concentration of unknown using pKa and molarity of known solution? Watch

sam013
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I carried out a titration using ethanoic acid and 0.1 mol dm^-3 of NaOH solution. I have that the pKa of ethanoic acid is 4.45.

The volume of NaOH at the equivalence point is 25 cm^3. The volume of ethanoic acid used was 20 cm^3.

How do you work out the concentration of ethanoic acid from that?

Do you use the Henderson Hasselbalch equation? I'm unsure about where to start.

And how would you determine the associated error?

A step by step explanation would be helpful!

Thanks in advance.
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charco
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(Original post by sam013)
I carried out a titration using ethanoic acid and 0.1 mol dm^-3 of NaOH solution. I have that the pKa of ethanoic acid is 4.45.

The volume of NaOH at the equivalence point is 25 cm^3. The volume of ethanoic acid used was 20 cm^3.

How do you work out the concentration of ethanoic acid from that?

Do you use the Henderson Hasselbalch equation? I'm unsure about where to start.

And how would you determine the associated error?

A step by step explanation would be helpful!

Thanks in advance.
For a kick off the pKa of ethanoic acid is 4.75, not 4.45

TBF you dont need pka for this ...

You work out the equivalence using the moles...

Moles of ethanoic acid = 0.02 x 0.1 = 0.002 mol, this equals the moles of NaOH

You needed 0.025 ml of NaOH so the molarity = 0.002/0.025 = 0.08 M
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Borek
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This is a simple stoichiometry and you don't need pKa for that (besides, pKa of acetic acid is 4.75, not 4.45). See explanation here: http://www.titrations.info/titration-calculation
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