Question

A solution of NaOH has an unknown concentration. When 1.396 g of potassium hydrogen phthalate (KHP a monoprotic acid frequently used as an analytical standard) is titrated with the sodium hydroxide the end point is 42.54 mL. Use this information to compute the concentration of NaOH in the solution. The molar mass of KHP is 204.22 g mol1. [OH mol L

Answer 1

Molar mass of KHP = 204.22 gmol^-1.

Weight of KHP which has been titrated using NaOH solution = 1.396 g = 1.396g/204.22 gmol^-1. = 6.84 x 10^-3 moles

Since KHP is a monoprotic acid which means only 1 mole of proton will be released from 1 mole of KHP.

So, 6.84 x 10^-3 moles of H⁺ will be neutralised by 6.84 x 10^-3 moles of OH^-.

Volume of NaOH solution required to reach end-point of titration = 42.54 ml

Therefore, strength of NaOH solution will be = 6.84 x 10^-3 moles / 42.54 ml = 1.61 x 10^-4 moles/ml

1 mL = 10^-3 L

So, strength of NaOH solution in molL^-1= 1.61 x 10^-4 moles/10^-3 L= 0.161 molL^-1.