which of following compounds cannot be used as a buffer?

[Smooth Operater]

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which of following compounds cannot be used as a buffer?
a. HBr
b. HCN
c. HF
d. HNO2
e. NH4+

I know buffer is made of weak acid and weak base. So, I chose HNO2 since it is a strong acid. But the correct answer is HBr.

How would you rationalize each choice to get the right answer? Thanks!

 

[Ex_EE]

HNO2 is ntirous acid a weak acid not nitric acid HNO3. HBR is hydrobromic and is strong.

 

[Smooth Operater]

how come not HF then?

 

[shushu]

HF is weak. the acidic tread....increases from left to right and down.

 

[Ex_EE]

Check out the followin pka table. The stronger the acid the worse the buffer. HBR is way up there.
http://www.science.uwaterloo.ca/~cchieh/cact/tools/pka.html

 

[celeron_266]

HBr for sure

although HF is very corrosive...its a weak acid