[jwright]

I am looking for a good demonstration on the biological significance of buffers. I envision a simple demo in which acid/base is added to water, and the pH changes; followed by adding acid/base to a buffered solution and no change is observed. If anyone has suggestions about this I would be quite grateful. In a related question, can a demonstration like this be done with a 0.1M sodium acetate/acetic acid buffer solution?
Thanks

[cliverlong]

Interesting question.

What came to my mind is the following.

1. How do you intend to measure the pH as you add acid and base? The standard (only?) technique is to titrate. Now I'm thinking as you ad the acid or base that the buffer will try to resist the change in pH. So how will this affect the measurement? How do you intend to measure the pH? I'm thinking that using an indicator that changes colour over a certain pH range won't be useful as you really want to show the pH not changing (much). So maybe a pH meter is needed?

2. Don't forget the question is asking you about the biological significance of buffers - so don't spend all your time on the behaviour of the buffer without considering the biology. Where do buffers occur in biolgy and why are they important? (I would suggest discussing two different examples would be needed).


Clive

[jwright]

I was thinking of using an indicator that changes color. In one beaker (with water and indicator) the acid added would show a color change, whereas in the second beaker (buffer and indicator) the acid added would not cause a color change, as the pH would be held in check.

And, yes, I will discuss a few examples of buffers in the body, the demonstration is simply a way to help the students remember what buffers do.

Thanks.

[Borek]

It is all about selecting correct buffer, correct indicator and correct amount of base/acid added. I you want to start with pure water its pH will be around 5.6, so you want an indicator that changes color in this area. Perhaps chlorophenol red?

http://www.titrations.info/acid-base-titration-indicators-preparation#chlorophenol-red

pH 5.6 buffer means citrate (assuming you need something easy to find).