What volume of 10.0 M NaOH is needed to prepare a buffer with a pH of 7.79 using

Question

What volume of 10.0 M NaOH is needed to prepare a buffer with a pH of 7.79 using 31.52 g of TrisHCI? Express your answer in milliliters using two significant figures ± Preparation of a Iris Butter In the study of biochemical processes, a common buffering agent is the weak base trishydroxymethylaminomethane, (HOCH2)3CNH2, often abbreviated as Tris. At 25 °C, Tris has a pKb of 5.91. Hints 6.7 mL Submit The hydrochloride of Tris IS (HOCH2)3 CNH3C1, which can be abbreviated as TrisHCi. My Answers Give Up Correct This procedure represents only one of many ways to prepare a buffer. The exact method chosen depends on the reagents and glassware available as well as the accuracy required for the pH Part B The buffer from Part A is diluted to 1.00 L. To half of it (500. mL), you add 0.0300 mol of hydrogen ions without changing the volume. What is the pH of the final solution?

Explanation / Answer

PH = PKa + Log [Moles of Tris]/[moles of Tris H+]

6.64 = 8.09 log [Moles of Tris]/[moles of Tris H+]

log [Moles of Tris]/[moles of Tris H+] = -1.45

[Moles of Tris]/[moles of Tris H+] = 10^-1.45 = 0.03548

Moles of Tris = 0.03548

(Moles of Tris H+] = 15.76 Tris HCl/157.6g of Tris HCl = 0.1

molesof Tris + moles of Tris H+ = 0.1

Moles of TrisH+ = 0.1/1.03548 = 0.09657

Moles of tris = 0.1-0.09657 = 0.00343

L HCl = 0.00343/10 = 0.000343 L

= 0.343 ml

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