Calculate the pH of two buffer systems to compare the differences in pH. One contains 1.0 M NH3 and 3.0 M NH4Cl. (Ka of NH4+, is 5.6x10^-10). The other contains 1.0 M NH3 and 5.0 M NH4Cl. (Ka of NH4+, is 5.6x10^-10).
It's just a matter of substituting into the Henderson-Hasselbalch equation.
pH = pKa + log[(base)/(acid)]
Convert Ka to pKa by pKa = -log Ka
Thank you!
To calculate the pH of a buffer system, we need to use the Henderson-Hasselbalch equation, which is given by:
pH = pKa + log ([A-] / [HA])
Here, [A-] represents the concentration of the conjugate base (NH3), and [HA] represents the concentration of the weak acid (NH4+).
For the first buffer system with 1.0 M NH3 and 3.0 M NH4Cl:
1. To find the concentration of NH4+, we need to consider that NH3 reacts with NH4+ to form NH4OH according to the following equation:
NH3 + H2O ↔ NH4+ + OH-
Since the concentration of NH3 is given as 1.0 M, the concentration of NH4+ is also 1.0 M.
2. Calculate the concentration of NH3 in the buffer solution:
Using the equation NH4Cl ↔ NH4+ + Cl-, we know that the concentration of NH4Cl is 3.0 M. Therefore, the concentration of NH4+ is also 3.0 M.
Since NH3 and NH4+ have a 1:1 stoichiometric ratio, the concentration of NH3 is also 3.0 M.
3. Use the Henderson-Hasselbalch equation to calculate the pH:
pH = pKa + log ([A-] / [HA])
pH = pKa + log (3.0 / 1.0)
The pKa value given is 5.6x10^-10. Therefore,
pH = -log(5.6x10^-10) + log(3.0)
pH ≈ 9.2
For the second buffer system with 1.0 M NH3 and 5.0 M NH4Cl, you can follow the same steps to calculate the pH. Just substitute the appropriate concentrations of NH3 and NH4+ into the Henderson-Hasselbalch equation.
pH = pKa + log ([A-] / [HA])
pH = -log(5.6x10^-10) + log(5.0 / 1.0)
Calculating this expression will give you the pH of the second buffer system.