Calculate pH of 0.1% w/v methylparaben solution.

General information:

Methylparaben (molecular weight = 152.14 g/ mole) acts as a weak acid in solution. It has a pKa value of 8.4 at 25 °C.

Calculation:

First, the concentration has to be expressed in terms of Molarity (moles/liter) as the following:

0.1 % w/v = 0.1 g/ 100ml

 Next, pH is calculated using online pH calculator or by applying the equation used for pH calculation for a solution containing a weakly acidic compound as the following (pKa = 8.4, Ka = 4.0×10^-9):

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Calculate pH of 0.1% w/v methylparaben sodium solution.

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