You have made 1L of a 0.1M HEPES buffer, and now you need to adjust the...

You have made 1L of a 0.1M HEPES buffer, and now you need to adjust the pH to 7.7. Calculate how much of a 0.5 M NaOH solution you would need to add. I was told to use Henderson-Hasslebach, I'm not sure how to do this one

Expert Solution

HEPES pKa = 7.5

pH = 7.7

moles of HEPES = 0.1 x 1 = 0.1

moles of NaOH = 0.5 x V

HEPES + NaOH --------------------------> salt

0.1 0.5 V 0 -------------------> initial

0.1-0.5 V 0 0.5 V ------------------> after reaction

Henderson-Hasslebach

pH = pKa + log [salt / HEPES]

7.7 =7.5 + log (0.5 V / 0.1 -0.5 V)

1.585 =(0.5 V / 0.1 -0.5 V)

-0.792 V + 0.1585 = 0.5 V

1.292 V = 0.1585

V = 0.1226 L

volume of NaOH =122.6 mL needed

queen_honey_blossom answered 2 years ago

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