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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: socomplicated on March 13, 2005, 05:09:25 AM

Title: buffers
Post by: socomplicated on March 13, 2005, 05:09:25 AM

to make a 25mM buffer with pH5.2 i add 25mM ethanoic acid with 25mM sodium ethanoate. after adjusting the pH, the buffer will still be 25mM. will this also be the case if i use 25 mM Tris-base and 25 mM phosphoric acid? will i still get a buffer with 25mM after adjusting the pH to 5.2 with the phosphoric acid?

the first one is a conjugate pair (ethanoic acid and sodium ethanoate), while the second one is not a conjugate pair (Tris-base and phosphoric acid)   :-\

thanks.

Title: Re:buffers
Post by: Borek on March 13, 2005, 06:50:21 AM

Quote from: socomplicated on March 13, 2005, 05:09:25 AM

to make a 25mM buffer with pH5.2 i add 25mM ethanoic acid with 25mM sodium ethanoate. after adjusting the pH, the buffer will still be 25mM. will this also be the case if i use 25 mM Tris-base and 25 mM phosphoric acid? will i still get a buffer with 25mM after adjusting the pH to 5.2 with the phosphoric acid?

The key question is: how is the buffer molarity defined?

Title: Re:buffers
Post by: socomplicated on March 13, 2005, 07:04:06 AM

Quote from: Borek on March 13, 2005, 06:50:21 AM

The key question is: how is the buffer molarity defined?

i know how to calculate the buffer molarity, but in some cases  i don't have time to do it, but only have to be sure, so my question is i know that a conjugate pair act that way, but how about a non conjugate pair? do you know it?