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I'm preparing for an experiment to investigate some factor affecting buffer capacity. At the moment, I'm looking at using a $\ce{NH_3}$ ($2\,\mathrm{M}$) $+$ $\ce{NH_4Cl}$ buffer, but I'm not sure which factor to test. My research tells me that only the concentrations of each will affect buffer capacity, and that the ratio of their concentrations will affect the $\mathrm{pH}$ of the buffer (by the Henderson-Hasselbalch equation). Are there other factors which I can test, because I'm trying to make it a bit more interesting? As far as I can tell, something like temperature won't affect buffer capacity.

As far as the actually experiment goes, what would be the best way to measure buffer capacity? I could just do a titration and record the $\mathrm{pH}$ as I go, but I'm thinking of using an indicator and measuring absorbance. I'm open to any ideas here, because I'm struggling to think of anything "out of the box"?

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As far as I can tell, something like temperature won't affect buffer capacity.

In this particular case, I wouldn't be too sure about it. Isn't it conceivable that your buffer will lose ammonia upon heating?

Did you already decide about the pH indicators? For the lower end, thymol blue might be a good choice. The supplementary data to J. Mater. Chem. B, 2015,3, 2801-2807 contains a UV/VIS spectrum of this indicator.

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  • $\begingroup$ What do you mean by "lose ammonia"? $\endgroup$ – deusy May 13 '15 at 10:09
  • $\begingroup$ @deusy You are having an aqueous solution of a gas. I would expect evaporation of a part of ammonia if you heat it up (too much). $\endgroup$ – Klaus-Dieter Warzecha May 13 '15 at 13:59

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