Question

Which of the following, when added to 1 liter of a 1.0 M NH3 solution would result in a buffer solution? Assume the volume remains at 1 liter.

a) 0.4 mole NaC2H3O2

b) 0.6 mole HNO3

c) 1.5 mole HClO4

d) 0.5 mole HCN

e) 0.5 mole NaOH

Answer 1

Buffer is a mixture of Weak acid and its conjucate base

or a mixture of weak base and its conjucate acid.

a) 0.4 mol Na₂C₂H₃O₂ + 1.0 mole NH₃ = Both are bases hence it can not act as buffer

b) 0.6 mol HNO₃ + 1.0 mol NH₃ --> 0.6 mol NH₄NO₃ + 0.4 mol NH₃

Yes it is a buffer mixture because it is a mixture of weak base ( NH₃) with conjucate acid (NH₄⁺)

c) 1.5 mol HClO₄ + 1.0 mol NH3 ---> 1.0 mol NH₄ClO₄ + 0.5 mol HClO₄

No it is not a buffer because it is a mixture of a strong acid (HClO₄) and its conjucate base (ClO₄^-)

d) 0.5 mol HCN + 1.0 mol NH3 => It is a mixture of weak acid and weak base.

f) 0.5 mol NaOH + 1.0 mol NH3 => It is a mixture of strong base and weak base.

Answer is option b) 0.6 mol HNO3