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.
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.
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
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.
To determine which combination of solutes would result in the formation of a buffer solution, we need to understand the characteristics of a buffer solution. A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. Buffer solutions are typically composed of a weak acid and its conjugate base, or a weak base and its conjugate acid.
Let's look at each combination and analyze them:
A) NH3 and HCl in a 2:1 molar ratio: In this combination, NH3 is a weak base, and HCl is a strong acid. A strong acid and a weak base do not form a buffer solution because a strong acid will completely dissociate into ions, resulting in a significant change in pH.
B) HCl and NaOH in a 1:2 molar ratio: In this combination, HCl is a strong acid, and NaOH is a strong base. Both compounds will completely dissociate into ions, resulting in the formation of NaCl (a salt) and water. This does not form a buffer solution.
C) NH3 and NH4Cl in a 2:1 molar ratio: In this combination, NH3 is a weak base, and NH4Cl is the ammonium salt of a weak acid, NH4+. The ammonium salt will dissociate to some extent, producing NH4+ ions and Cl- ions. NH3 will react with the NH4+ ions, keeping the concentration of OH- ions relatively stable. This forms a buffer solution.
D) NaOH and CH3COOH in a 1:1 molar ratio: In this combination, NaOH is a strong base, and CH3COOH is a weak acid. A strong base and a weak acid do not form a buffer solution, as the base will completely dissociate.
The molar ratio is important because it determines the relative concentrations of the weak acid/base and its conjugate base/acid. A proper buffer solution requires a sufficient concentration of the weak acid/base and its conjugate species to resist changes in pH. The 2:1 molar ratio in option C ensures a higher concentration of both NH3 and NH4+ ions, allowing the solution to act as a buffer.
In summary, out of the given combinations, only option C, NH3 and NH4Cl in a 2:1 molar ratio, would result in the formation of a buffer solution because it involves a weak base (NH3) and its conjugate acid (NH4Cl) in appropriate concentrations.