I got 7.3-9.3 for a and im not sure how to do b and c The weak base commonly kno
ID: 797204 • Letter: I
Question
I got 7.3-9.3 for a and im not sure how to do b and c
The weak base commonly known as Tris [ tris(hydroxymethyl)aminomethane], has pKa = 8.3 at 20 degree C and is commonly used in biochemical buffer solutions. At what pH would you expect Tris to act as a buffer in a solution that has equal molar concentrations of base and its conjugated acid? What is the pH after addition of 3.8 mmol NaOH to 100 ml of buffer with pH found in part a) and total concentration (base and conjugate acid) of 300 mM? What is the pH after addition of 6.3 mmol HN03 to the same buffer as in part b)?Explanation / Answer
b) Conc of base = Conc of conjugate acid = 300 / 2 = 150 mM
Moles = 0.15 x 0.1 = 0.015 moles
pH = pKa + log (Salt + X / base - X)
where X = NaOH
=> pH = 8.3 + log (0.015 + 0.0038 / 0.015 - 0.0038) = 8.525
c) H = pKa + log (Salt - Y / base + Y)
where Y = HNO3
=> pH = 8.3 + log (0.015 - 0.0063 / 0.015 + 0.0063) = 7.911
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