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I'm trying to find the effect of pH on living things like E. coli and such. At first I thought of using a buffer solution which maintains its level of pH, but it's possible that the inactive ions of each buffer have their own effect on living things that I can't account for. On the other hand, I could use hydrochloric acid and sodium hydroxide at different concentrations by diluting it. This will be a little bit more effort (I'll be diluting the acid and base myself), but much cheaper than the buffers, and I'll know that the only other ions present beside H+ and OH- are just Na+ and Cl-, the ingredients of table salt. According to this paper, the effect of pH on the population also depended on the acid (HCl vs lactic acid).

I would like a second opinion on this: If I'm investigating the effect of pH on growth of living things, do I use specially made buffers or just properly diluted HCl and NaOH?

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  • $\begingroup$ What makes you think that Na+ and Cl- can be ignored? Just because they're what makes up table salt does not mean they are harmless. I am not saying they can't be ignored for the purposes of this experiment either, just pointing out that you may be jumping to conclusions. $\endgroup$ – terdon Oct 21 '13 at 22:36
  • $\begingroup$ @terdon Not saying they are to be ignored, but if anything, these are controls. I KNOW that they're there. OTOH, I have no idea what went into those buffers. $\endgroup$ – Greg Oct 21 '13 at 22:37
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That is a variable that you have the pleasure defining yourself. Just know that using a buffer will introduce other atoms that could affect the "living things". Conversely, if you don't use a buffer, it is likely that the pH of your "living things" will be easily altered by the metabolism of your living things (IMHO, this is worse).

I don't know the details of your project, but recommend:

-use a buffer like.. Tris, phosphate... -use 10 mM Tris-Cl without any extra electrolyte (aside of the HCl or NaOH that you use to modulate the pH of your buffer to different pH's that you want to test) -e.g. Tris-Cl pH 7, 8, 9.. or Phosphate pH 2,3,4,5,6,7,8,9..

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