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08_Lecture0

# 072 set up h h ph 8072 log 3525 8218 now

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Unformatted text preview: adjust the ratios and create a new pH for the buffer… adjust Buffers do not prevent pH changes but they do resist changes they • Determine the pH of a buffer made from 0.25 M Tris hydrochloride and 0.35 M Tris. (Tris is a weak base, abbreviate as B; Tris hydrochloride is the conjugate acid BH+; the pKa of the acid is 8.072) Set up H-H: • pH = 8.072 + log [.35/.25] = ….. 8.218 • Now if the buffer is “attacked” by adding enough HCl to make it 0.010 M, what will be the new pH? (Note that if 0.010 M HCl is just found in water the pH would be ~ 2.00.) 8.189 • BH+ would now be a bit more, B would now be less. Some acids produce more than one H+; some bases accept more than one H— these are known as POLYPROTICS When the amino acid proline is fully protonated it will have two acid H+ (Proline is one of the main components of our collagen). Ka1 = 1.1 x10–2; Ka2 = 2.3 x10–11; + • What is the pH of 0.010 M solution? • Consider two reactions reaching equilibrium • H2Pro+ H+ + HPro Ka1 = [H+][HPro]/[H2Pro+] HPro • HPro H+ + Pro– 2 Ka2 = [H+][Pro–]/[HPro]] • Take advantage of a simplifying assumption in Ka2. Polyprotic Acids: Twice as Nice! • H2CO3 and others. Each H+ has its own Ka • Several components are present at same time: H2CO3, HCO3–; CO32–; H+ There is a fraction of species for each! • Fo...
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