Question on Preparing Buffer Solutiosn

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Link the Worlds
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Question on Preparing Buffer Solutiosn

Hello all, any help on this problem would be greatly appreciated...

I'm really lost for this assignment and don't even know where to begin...

I'm supposed to describe the preparation of 15 liters of .07 M phosphate buffer, pH 7.00 starting from:

a) 1.00 M KH2PO4 and 1.00 M Na2HPO4

What I do know is that the pKa of H2PO4 is 6.82, and I was told this is the only pka necessary, but I don't know why the pka of HPO4 is not necessary.

protoldo
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Hola, In one of the first

Hola, In one of the first Methods in Enzymology  are described how to do the most used buffers in the lab In any web and probably in this forum you can search the recipes. For sodium phosphate buffer 0.2 M pH 7 starting of 0.2 M of monobasic and 0.2 M dibasic  phosphates mix 39ml of the first and 61 ml of dibasic. Make a try with a little volume with the 1M buffers and if you get the correct pH prepare 10,5l of the 1M mix and dilute to 15l with water to get the 15l. of 0.7M buffer. Good luck