A solution of sodium hydroxide (NaOH) was standardized against potassium hydroge

Question

A solution of sodium hydroxide (NaOH) was standardized against potassium hydrogen phthalate (KHP). A known mass of KHP was titrated with the NaOH solution until a light pink color appeared using phenolpthalein indicator. Using the volume of NaOH required to neutralize KHP and the number of moles of KHP titrated, the concentration of the NaOH solution was calculated.

Molecular formula of Potassium hydrogen phthalate: HKC8H4O4

Mass of KHP used for standardization (g) 0.5151

Volume of NaOH required to neutralize KHP (mL) 13.1955

Calculate the concentration of NaOH solution in (mol/L)

Explanation / Answer

The number of mols of HKC8H4O4 = 0.5151 g / 204.22 g/mol = 0.00252 mol

As per the balanced equation of KHP and NaOH, 1 mol of KHP requires 1 mol of NaOH.

Hence -0.00252 mols of KHP obtained above rquires same number of mols of NaOH. Hence -

The number of mols of NaOH = 0.00252 mol

volume of NaOH required = 13.1955 mL

Therefore ,

Molarity of NaOH = (0.00252 mol)(1000) / (13.1955 mL) = 0.190 M

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