[big]

Which combinations of equal volumes of solution will result in buffer solutions?

I.   0.1 M HCl and 0.1 M NH₃
II.   0.1 M HNO₂ and 0.05 M NaOH
III.   0.05 M HNO₂ and 0.05 M NH₃

So the answer key tells me that the answer is I and III. Since HCl is a strong acid, it reacts completely with NH₃ to form 0.1 M NH₄⁺, so how is I a buffer solution? And why is II NOT a buffer solution if the NaOH reacts completely with 0.05 M HNO₂ to form 0.05 M NO₃^-, which leaves 0.05 M HNO₂? Shouldn’t the answer be II and III?

[rabolisk]

My intuition says that I and III are not buffers, and that only II is...

[AWK]

Answer I and III is for
Which combinations of equal volumes of solution will not result in buffer solutions?

[big]

well before I looked it up though, it says here http://answers.yahoo.com/question/index?qid=20080901014919AA4SaZY that HNO2/NH3 could kind of be a buffer. is that wrong?

[Borek]

Whoever answered the question at yahoo has no idea what he is talking about.

The equilibrium for this reaction lies far to the left
NH3 + HNO2 <==> NH4+ + NO2-

This is complete nonsense. 0.025M solution of ammonium nitrite (assuming it exists and is stable) contains about 0.1% of nitrous acid and 0.1% of ammonia. That means equilibrium lies far to the right, unless I don't know which hand is which.

For sure buffer capacity of this solution is higher than buffer capacity of sodium chloride solution, but I would not call it a buffer.

[big]

This is complete nonsense. 0.025M solution of ammonium nitrite (assuming it exists and is stable) contains about 0.1% of nitrous acid and 0.1% of ammonia. That means equilibrium lies far to the right, unless I don't know which hand is which.

Just wondering, why does the equilibrium lie far to the right?

[Borek]

They are weak, but not not very weak, and they are still strong enough to neutralize each other.