A 50.0 mL sample of HCl required 25.81 mL of 0.1250 M KOH for neutralization. What is the molarity of the acid?

0.065M

Explanation:

The reaction expression is given as:

         HCl   +   KOH  →  KCl + H₂O

Given parameters:

Volume of KOH  = 25.81mL  = 0.02581L

Molarity of KOH = 0.125M

Volume of HCl  = 50mL  = 0.05L

Unknown:

Molarity of the acid  = ?

Solution:

To find the molarity of the acid, HCl, let us use the mole concept.

  First, find the number of moles of the base, KOH;

Number of moles of KOH = molarity of KOH x volume of KOH

   Number of moles of KOH  = 0.125 x 0.0258 = 0.003225mol

From the balanced reaction equation:

   1 mole of KOH reacted with 1 mole of HCl

   0.003225mol of KOH will react with 0.003255mole of HCl

Molarity of HCl  =

Molarity of HCl  =   = 0.065M