[satirical_snowman]

Hey guys,

I'm working on a lab about buffers in my AP Chem class, but my teacher didn't really explain what a buffer was. He just said it has something to do with keeping pH constant? So here's my question:

Out of the following:
1. 30 mL distilled water
2. 30 mL 0.1 M acetic acid
3. 30 mL 0.1 M sodium acetate
4. 15 mL 0.1 M acetic acid mixed with 15 mL of 0.1 M sodium acetate
5. 30 mL 0.1 M acetic acid mixed with 1.5 mL 1 M NaOH
6. 30 mL pH buffer 7 stock solution

Which ones would be buffers? What makes them that way? In general, how do I tell if something is a buffer or not?
(Just to take a guess, I would think that 4, 5, and 6 would be buffers?)

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Thanks,
satirical_snowman

[Borek]

Have you read what wikipedia (or any other source) has to say on buffers?