[docpar]

Hi,
How would I make a buffer with the following requirements:
-Have 1 L of the buffer
-The buffer must have a pH of 5.35
-Total concentration of the acid/base in the solution must be under .100 M

So, how would this be made (how many g of what, etc.)?

I think a citric acid buffer would be good for this, and I think I should use the henderson-hasselbach equation, but dont know how...

thanks for any help

[Borek]

You may try with acetate buffer - even if it not the best one, it is pretty easy to calculate.

Assume concentratin of acetic acid + concentration of acetate to be 0.1M - that will give you one equation.

Use Henderson-Hasselbalch - that will give you second equation.

Then it is just a matter of simple algebra.

[docpar]

You may try with acetate buffer - even if it not the best one, it is pretty easy to calculate.

Assume concentratin of acetic acid + concentration of acetate to be 0.1M - that will give you one equation.

Use Henderson-Hasselbalch - that will give you second equation.

Then it is just a matter of simple algebra.

So would the first equation be log(x/(.1-x))  ?  And then I just plug that into the Henderson-Hasselbach equation?

That would lead to -0.6 = log(x/(0.1-x))  ?  I have one more question.  The requirements say that the total concentration of the acid and bases need to be UNDER 0.1 M.  Does that mean i can still assume that the concentration of acetic acid + concentration of acetate to be 0.1 M?

Thanks for the help

[Borek]

x/(.1-x) looks about right.

If you are really worried about these concentrations, assume sum to be 0.05

[docpar]

x/(.1-x) looks about right.

If you are really worried about these concentrations, assume sum to be 0.05

Ok, got it! I'm sorry, but I'm still confused about one other thing  Say I get for the concentration values required that the [acid]=.02 M and [base]=0.03M
Does that mean I have to add both the acid and base in those concentrations or just the acid in that concentration, because when you add a weak acid or base to water, doesn't that create an equilibrium reaction.  In other words, how would I actually make this buffer?  Do I need to just add 0.02 M of acid, or both 0.02 M of acid and 0.03M of base. 

thanks again for all the help

[Borek]

You may mix 0.02 of acid and 0.03 of salt.

You may mix 0.05 of acid and 0.03 of strong base.

You may mix 0.05 of salt and 0.02 of strong acid.

Take your pick.

[docpar]

You may mix 0.02 of acid and 0.03 of salt.

You may mix 0.05 of acid and 0.03 of strong base.

You may mix 0.05 of salt and 0.02 of strong acid.

Take your pick.

That makes sense.  thanks