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Describe how one would prepare in the laboratory 1.00 liter of a 50 millimolar sodium phosphate buffer solution having a ph of 7.0. The pKa values of phosphoric acid, H3PO4, are 2.14, 6.86, and 12.4. Assume reagent grade 80% (w/w) phosphoric acid solution and a standardized 0.100 M solution of NaOH available and needed glassware.

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Trinidad TremblayLv2

17 Dec 2019

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Many of the biochemistry experiments and cell cultures need to be pH buffered in a narrow range. Many different buffers are used, but phosphate buffers are a classic choice. Suppose you need to make a 1 liter phosphate buffer solution with a pH of 7.10. You add 15.0 grams of sodium dihydrogenphosphate (NaH₂PO₄) to a 1.00 liter flask. How many grams of sodium hydrogen phosphate (Na₂HPO₄) do you need to add to obtain the desired pH buffer solution? The pK_a values for the three ionization states of phosphoric acid are 2.16, 7.21 and 12.32. The exacting nature of these types of solutions requires that you be within 0.25 grams to receive credit for this question.

2. Phosphoric acid (H3PO4) is a triprotic acid with the following pKa values: pKa1 = 2.15 pKa2 = 7.20 pKa3 = 12.35

a). You wish to prepare a 1.000 L of a 0.0450 M phosphate buffer at pH 6.8. Which of the following salts do you use (PICK 2) and what mass of each salt will you add to the mixture? H3PO4 (M.W.= 97.995) KH2PO4 (M.W.=136.086) Na2HPO4 (M.W.=141.959) AlPO4 (M.W.=121.953) 2

b). A concentrated phosphate buffer known as âphosphate buffered salineâ (or PBS) is made with the salts you choose from above in addition to NaCl and KCl. The 10x concentrated solution has a pH ~6.8 and the 1x concentrated (i.e., diluted with water) solution is ~7.1. Why?

c). You accidently grabbed the 10x concentrated phosphate buffered saline (or 10xPBS) instead of the 1xPBS solution and start to adjust the pH of your buffer with NaOH to reach your desired buffer pH. You notice it is taking much more base than with your usual 1xPBS buffer. Why?

it's the post lab question. I'm confused how to do this. I solved for the molar ratio of B to A which is 2.01:1 and I don't know where to go from there

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