I am an electronics guy with not so much knowledge of chemistry. I would like to prepare a pH 7 buffer to test pH meters.

All web references I have found so far describing how to make a phosphate buffer use disodium phosphate (Na2HPO4) and Monosodium phosphate (NaH2PO4) as ingredients.

I have a good supply of 85% phosphoric acid and solid sodium hydroxide. Can I make a pH 7 buffer from these ingredients instead or is there a catch?

  • $\begingroup$ Generally you'd get a standard solution to calibrate your meter. $\endgroup$ – canadianer Apr 4 '15 at 0:06

You should be able to do this with little trouble. The only caveats:

  • Make a stock solution of phosphoric acid and also of NaOH. When you add them to each other to make your buffer, heating could be a problem, much moreso than if you were using the mono- and di-basic sodium phosphate salts. So you may want to cool on ice when mixing these compounds.

  • You can calculate approximately how much NaOH and phosphoric acid to mix in order to get a pH 7 result, but it's best to use a pH meter to verify that you've reached pH 7.

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