Question

How do I know if a solution will be a buffer? What are the criteria? Does the concentration matter?

For example:

Which of the following will be a buffer?

i)0.1M NaOH and 0.1M HBr

ii)0.2M HCl and 0.4M NaF

iii) 0.1M NH3 and 0.2M NH₄Cl

Answer ii) and iii)

I understand why iii) works but why does ii) work too?

Answer 1

For making a buffer solution ,weak acid and its conjugate salt is needed as in the case of third option ,

In 2nd one HCl + NaF = HF +NaCl ,so on reaction of gcl with NaF ,HF is produced which is weak acid and since concentration of NaF is more than HCl ,NaF will be left behind thus we have both weak acid and it's salt.so it is also a buffer