Calculate the volume (in ml) of 0.170 m naoh that must be added to 389 ml of 0.0543 m 3-(n-morpholino)propanesulfonic acid (mops) to give the solution a ph of 7.55. the pka of mops = 7.18.

3-(n-morpholino)propanesulfonic acid [MOPS] is used as a buffer specially in biological systems

When we add NaOH to it , it forms salt with it and there is a change in the pH of the solution

MOPS + NaOH ---> NaMOPS + H₂O

The Hendersen equation for estimation of pH of a buffer is

pH = pKa + log[salt]/[acid]

7.55 = 7.18 + log[salt]/[acid]

On solving

[salt] / [acid] = 2.344

moles of salt required = 2.344 X moles of acid

initial moles of acid present = 389 X 0.0543 = 21.12 mmoles

let the moles of base added = x mmol

As per equation each mole of base will react with one mole of MOPS

Therefore

moles of salt formed = x mmol

moles of acid left = 21.12-x

x = 2.344 (21.12-x)

x = 49.51 - 2.344x

x = 14.80 mmol

this is the millimoles of base required

So the volume of NaOH needed (mL) = moles / molarity = 14.80/0.170 = 87.05 mL

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