Question

A solution of 0.2 M HCl is mixed with 0.3 M NH₄Cl. Is this a buffer?

A.) Yes

B.) No

C.) impossible to tell

Answer 1

Note that for a buffer, we need:

either a weak acid and its conjugate base

or

a weak base and its conjugate acid

So... from HCl and NH4Cl:

HCl -> H+ and Cl- , strong acid

NH4Cl --> NH4+ + Cl-, this is a salt

note that NH4+ in solution will hydrolyse as follows:

NH4+(aq) + H2O(l) <--> NH3(aq) + H3O+(aq)

which is acidic

so

H3O+ and H+ from HCl will NOT FORM a buffer

since this is mostly acidic species

the only way we could make this a buffer will be exchanging HCl for NaOH, so NaOH + NH4+ --> NH3 + H2O + Na+

so NH3 ad NH4+ (weak base + conjugate acid) will be present

but this is not the case, so answer is

B) NO, n buffer is formed