Buffer Solutions: How to Create and Maintain Optimal pH Levels?

[TT0]

Homework Statement

Homework Equations

The Attempt at a Solution

From what I know, to make buffer solutions you need a weak acid or base and it's salt. Non of the options has this. What am I missing?

Cheers!

 

[Borek]

What is left after the reaction?

 

[TT0]

For reaction 1, the products are: Cl-, NH4+, NH3, H+ (as HCl is strong acid while ammonia is weak base)
For reaction 2, the products are: Na+, H2O, NO2- (NaOH is strong while nitrous acid is weak. No HNO2 because the H+ will react to form water so equilibrium will shift to the right in equilibrium HNO₂ → H⁺ + NO₂^-)
For reaction 3, the products are: NH3, NH4+, HNO2, NO2- (both are weak)

Reaction 3 is probably creates a buffer solution as they can accept or donate protons and the equilibrium will shift.
If acid was added to reaction 2, the NO2- will turn to nitrous acid but if base was added, nothing will happen, so not a buffer solution.
If acid was added to reaction 1, the equilibrium NH₃ + H⁺ ↔ NH₄⁺ will shift to the right and if base was added, the equilibrium will shift to the left so it is a buffer solution.

Answer is D.

Are my explanations correct?

Cheers!

 

[Borek]

Nope, you need a comparable amounts of conjugate acid and base for the buffer to exist.

 

[TT0]

I see, I change my mind on reaction 2. There will be around 0.5 M of HNO₂ and NO₂^- so it will be a buffer solution. So then the answer is E?

Cheers!

 

[Borek]

What is present after the reaction in the 3rd mixture?

 

[TT0]

NH3, NH4+, HNO2, NO2-

 

[Borek]

In what (approximate at least) concentrations?