Question

You must make a MOPS-KOH buffer (500 ml at 60mM) at a pH value of 7.5....


You must make a MOPS-KOH buffer (500 ml at 60mM) at a pH value of 7.5. Assume that the pKa is 7.28. MW of MOPS is 209.3g/mol and 2M is available

Show the weak acid base reaction. The sulfonamides acid quickly loses its proton.
Calculate the grams of MOPS acid salt form needed.
Calculate the ml of 2M KOHLER needed

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Homework Answers

Answer #1

moles of buffer : ( 500 / 1000 ) x 60 x 10^-3 = 0.03

acid + salt = 0.03 ---------------> 1

pH of buffer = 7.5

pKa of aicd = 7.28

pH = pKa + log [salt / acid]

7.5 = 7.28 + log [salt / acid]

0.22 = log [salt / acid]

[salt / acid] = 1.66

salt = 1.66 acid -----------------> 2

acid + 1.66 acid = 0.03

2.66 acid = 0.03

acid = 0.0181

moles of acid = 0.0181

moles of acid salt = 0.0119

moles = mass / molar mass

0.0119 = mass / 209.3

mass = 2.491 g

MOPS acid salt = 2.491 g

volume of salt = volume of KOH
moles = 0.0119

molarity = 2 M

molarity = moles / vloume

2 = 0.0119 / volume

volume = 0.00595 L

volume of KOH = 5.95 ml

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