Which of the following solutions result in a buffer ?

Question

Which of the following solutions result in a buffer ?


a) 0.050 L of 0.250 M NH3 + 0.100 L of 0.250 M HCl


b) 0.100 L of 0.250 M NH4Cl + 0.050 L of 0.025 M HCl


c) 0.100 L of 0.250 M NH4Cl + 0.050 L of 0.250 M NaOH


d) 0.100 L of 0.250 M NH4Cl + 0.150 L of 0.250 M NaOH

Answer 1

b and c do, a and d do not.

For a buffer to exist, you must have sufficient quantities of a weak acid and its conjugate base. The reactions in b and c are incomplete, thus you're left with sufficient concentrations of NH4+ and NH3. In a and d, your reactions are complete, so you don't have both species present in solution.

Answer 2

YOu are looking for a weak acid and base pair. This is a tough one because all of them are paired with a strong acid or a strong base. Look at the resulting reactions. Amonnia and hydrochloric acid will produce ammonium chloride and have strong acid left over so no buffer Ammonium chloride and hydrochloric acid makes a lot of acid no buffer C however mkes some ammonia and has ammonium left over. That is a buffer