Question

NH3/NH4 buffer:

Mass NH4Cl used 1.3738g

volume NaOH used 21.2 ml

initial pH (0f the buffer) 9.6, pH after 1 drop HCl 9.03, pH after 10 drops HCl 8.91

Dilute NaOH solution

Initial pH 10.35

pH :1 drop HCl 10.21, 10 drops HCl 2.85

Acetate buffer (0.500)

Mass of CH3COONa * 3H2O 10.935

volume CH#COOH 44.3 ml

initial pH 4.89

1.0 ml of NaOH pH 4.93

initial volume 2.2

final volume 16.2

final pH 5.91

Acetate buffer (0.100)

Mass of CH3COONa * 3H2O 2.1603

volume CH3COOH 8.9 ml

initial volume 6.2

final volume 23.2

Initial pH 4.85

final pH 5.83

1. Show complete calculations for the buffering capacity of both the 0.500 M and 0.100 M acetate buffers.

2. Compare ability of your buffer solution to resist changes in pH with that of the strong base (NaOH). Why can the buffer resist the pH change? Comment on why NaOH does not function as a buffer.

3. How did the concentration of the buffers affect the buffering capacity? Explain your observations.

Answer 1

Buffering capacity : It resists the change in pH on adding the acid or base . By using the henderson hasselbalch equation we will have the data on buffering capacity.

pH=pKa + log [A^-]/[HA] . by using the different concentrations of buffers by taking the samples there is a lesser change in buffer having 0.1M has a higher buffer capacity.

if we add stong base NaOH it dissociates to OH- and reacts with acid and finally it produces one equivalent of base thats the reason NaOH doesnot function as a buffer.

OH^- + RH --> H₂O + R^-  

From the data we can conclude the buffering capacity with different concentrations sample with 0.1 have the higher buffer capacity [A^-][HA].