Question

What is the final concentration of a solution prepared by pipetting 10.00 mL of a 0.1284 M NaOH into a 25.00 mL volumetric flask and diluting with water to the mark?

Answer 1

Ans. Using:       M1V1 = M2V2 --- equation 1

Where, M1= molarity of solution 1, V1= volume of solution 1 (say, initial solution)

            M2= molarity of solution 2, V2= volume of solution 2 (say, final solution in volumetric flask)

Putting the values in equation 1-

            0.1284 M x 10.00 mL = M2 x 25.00 mL

            Or, M2 = (0.1284 M x 10.00 mL) / (25.00 mL) = 0.05136 M

Hence, molarity of final solution in volumetric flask = 0.05136 M

Note: M1V1 = (moles / L) x (L) = moles. That is M1V1 gives the number of moles of the solute is specified volume. Also since dilution with water does not change the number of moles of NaOH or other solute in the solution-

the number of moles of NaOH in initial solution = number of moles of NaOH in final solution.

Or, M1V1 = M2V2