Question

You have completed preparing your buffer and you are ready to go home, but your supervisor informs you just before you leave that you should also prepare 0.5L of 1M Tris-base, 0.5mM EDTA, pH 7.4. The molecular weights are: Tris-base - 121.14, and EDTA -292.25. Show your calculations in preparation of this buffer. The pH of this solution will be basic. In general terms, state how you will pH to 7.4?

Answer 1

First what I would do is ask my supervisor why would I need a 1M Tris stock with only 0.5 mM EDTA? It does not make much sense.

Answer 2

I think you might mean 1M Tris and 0.5M EDTA for stock solutions - these are the ones I use every day. However, to answer the question you would multiply 121.4g (the weight of 1 mole of tris base by 0.5 (because you only want 0.5l). Similarly, multiply the weight of 1 mole of EDTA (292.5g) by .0005 since the concentration is half of one thousandth of 1M, then multiply by 0.5 since you are only making 0.5 litres. If you want to work it out then I can check back for you. Best wishes