Question

Explain clearly which out of the following combinations of solutes would result in the formation of a buffer solution?
A) NH3 and HCl in a 2:1 molar ratio
B) HCl and NaOH in a 1:2 molar ratio
C) NH3 and NH4Cl in a 2:1 molar ratio
D) NaOH and CH3COOH in a 1:1 molar ratio

And: Why is the molar ratio important?
Thanks for the help.

Answer 1

For a buffer you want a weak acid and its conjugate base OR a weak base and its conjugate acid.
A In a 2:1 molar ratio you will get all of the HCl used up and form NH4Cl so the final solution will be NH3 and NH4Cl which is a buffer. You look at the others.

Answer 2

Here is what I got :
a) formation of a buffer solution
B) strong acid and strong base, no formation of a buffer solution.
C) formation of a buffer solution
D) strong acid and weak base, formation of a buffer.

Am I correct?
thank you

Answer 3

Right on all but D. Since you have EXACTLY 1:1 ratio that means that the strong acid will exactly neutralize the weak base leaving you with the salt ONLY. You have half of what you need but not the other half.