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22 January, 15:48

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.

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  1. 22 January, 16:07
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    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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