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Solution and answer to neutralization problem

A lab technician wants to determine the molarity of an unknown mono protic acid. What is the molarity of the solution if 13.61 mL if the acid is neutralized by 34.69 mL of 0.025 M KOH?

The definition for molarity can be used to produce the following equation.

moles solute = molarity x liters solution = M V

This means the moles of acid in a solution are calculated using

moles acid = Ma Va

The moles of base in a solution are calculated using

moles base = Mb Vb

the terms are defined as follows

Ma is the molarity of the acid

Va is the volume of the acid

Mb is the molarity of the base

Vb is the volume of the base

For a neutral solution at the end point of a titration the

moles of acid = moles base

Ma Va = Mb Vb

gather data

Ma = unknown = X

Mb = 0.025 M KOH

Va = 13.61 mL = 0.01361 L

Vb = 34.69 mL = 0.03469 L

substitute values

Ma Va = Mb Vb

X (0.01361 L) = (0.025 M KOH)(0.03469 L)

solve for "x"

X = (0.025 M KOH)(0.03469 L)/(0.01361 L)

X = (0.00086725 M )/(0.01361 ) where liters cancel

X = 0.06372 M round to 2 sf because the molarity of the KOH has only "2" sf.

X = 0.064 M answer

Dr. Walt Volland, All rights reserved 1999-2000

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