. On your first day working in a biochemistry research lab, you are asked to prepare...

. On your first day working in a biochemistry research lab, you are asked to prepare 500 mL of a 0.15 M sodium phosphate buffer solution at pH 6.5. Your lab contains stock solutions of H3PO4, NaH2PO4, Na2HPO4, and Na3PO4, each at 0.5 M, as well as plenty of double-distilled water.(a). (6 points) What do you mix and in what amounts in order to prepare the desired buffer?

Solutions

Expert Solution

total no of mol of phosphatebuffer = M*V = 0.15*0.5 = 0.075 mol

pH of phosphate buffer = pka2 + log[Na2HPO4/NaH2PO4]

pka2 of H3PO4 = 7.2

[Na2HPO4] = x

[NaH2PO4] = 0.032-x

6.5 = 7.2 + log(x/(0.075-x))

x = 0.0125

[Na2HPO4] = x = 0.0125 mol

[NaH2PO4] = 0.075-x = 0.075-0.0125 = 0.0625 mol

volume of Na2HPO4 stock solution must take = n/M = 0.0125/0.5 = 0.025 L

= 25 ml

volume of NaH2PO4 stock solution must take = 0.0625/0.5 = 0.125 L

= 125 ml

25 ml +125 ml + rest add water up to 500 ml

so that desired buffer will be prepared.

queen_honey_blossom answered 1 year ago

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