titration by strong acid

[silverice]

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I figured this one out because the problem used drops and i assume we can't calculate that. although a drop is technically 0.2 ml(i know it cuz i'm into essential oil stuff and that's how to measure stuff sometimes), but i don't think us pre med kids need to know that. Therefore the only concept I have in mind was that Strong acid makes the solution a little acidic.

But is that enough? Am I missing any other concept? Is there any other way to solve this? what if only 1 drop of 12M HCL are added?

 

[milski]

I don't think they want you to do the math here. Just know that adding a few drops will lower the pH but adding a few drops won't lower it from 8 to 3.

 

[MedPR]

View attachment 18598

I figured this one out because the problem used drops and i assume we can't calculate that. although a drop is technically 0.2 ml(i know it cuz i'm into essential oil stuff and that's how to measure stuff sometimes), but i don't think us pre med kids need to know that. Therefore the only concept I have in mind was that Strong acid makes the solution a little acidic.

But is that enough? Am I missing any other concept? Is there any other way to solve this? what if only 1 drop of 12M HCL are added?

You're not missing anything. What you need to figure out to answer this question correctly is that you overtitrated with the KOH, but only by an amount that could be fixed (brought back to equivalence) by a few drops of strong acid. So the pka of the original, unkown acid, is a bit less than calculated.

Edit: Oops, I didn't even read the question. I was thinking this was the question about titrating with KOH then having to add acid back into it.

 

[lkthlttr]

The key term in this question is "buffered". You are supposed to understand that a buffer is used to protect a solution against wild changes in pH upon addition of acid or base. So you should be able to reason that a few drops of 12M HCl will make the solution more acidic, but not drastically so.

 

[MrNeuro]

You're not missing anything. What you need to figure out to answer this question correctly is that you overtitrated with the KOH, but only by an amount that could be fixed (brought back to equivalence) by a few drops of strong acid. So the pka of the original, unkown acid, is a bit less than calculated.

Edit: Oops, I didn't even read the question. I was thinking this was the question about titrating with KOH then having to add acid back into it.

LOOL I know what question your talking about

but ahh yeah i struggled with this technicality longer than i'd like to admit when does pH of a buffer change and when does it not...pretty much it always WILL change even if you add a very weak acid its going to change maybe by some insignificant value that can't be determined due to experimental error, but its ALWAYS going to change

edit: just be wary of changes that are significant i.e adding more conjugate to this buffer will probably change the pH but not by more than 1/100 (0.01)