It requires 23.2 mL of 0.250 M KOH to titrate 49.0 mL of an HCl solution of unknown concentration. Calculate the initial HCl concentration.

HCl + KOH ==> KCl + H2O

Note the ratio is 1 mol KOH = 1 mol HCl.

mols KOH = M x L = ?
mols HCl = mols KOH
MHCl = mols HCl/L HCl
Done.

To calculate the initial HCl concentration, we can use the concept of stoichiometry and the volume and concentration of the KOH solution used in the titration.

The balanced chemical equation for the reaction between KOH and HCl is:

KOH + HCl -> KCl + H2O

From the balanced equation, we can see that the stoichiometric ratio between KOH and HCl is 1:1. This means that 1 mole of KOH reacts with 1 mole of HCl.

Given that the volume of the KOH solution used is 23.2 mL and its concentration is 0.250 M, we can calculate the number of moles of KOH used:

moles of KOH = volume (in L) × concentration (in mol/L)
= 23.2 mL × (1 L / 1000 mL) × 0.250 mol/L
= 0.00580 mol

Since the stoichiometric ratio between KOH and HCl is 1:1, the number of moles of HCl in the solution is also 0.00580 mol.

Now we can determine the initial concentration of HCl by dividing the moles of HCl by the initial volume of the HCl solution, which is 49.0 mL (convert to L):

initial concentration of HCl = moles of HCl / volume of HCl solution (in L)
= 0.00580 mol / (49.0 mL × 1 L / 1000 mL)
= 0.118 M

Therefore, the initial concentration of the HCl solution is 0.118 M.