Question

Assume that you have 1, 2, 5, and 10 mL pipets and a 25 mL volumetric flask only. Describe in detail how you would prepare a solution with a concentration near 0.100 M from a 0.650 M stock solution using the glassware listed above. Calculate the final concentration of the diluted solution (it won't be exactly 0.100 M). It should be within 10% of 0.100 M. (Please see the Lab Skills for the accuracy on volumetric pipets and flasks.)

Answer 1

Explanation:

The given data is as follows.

      $V_{1}$ = 25 ml,          $M_{1}$ = 0.10 M

      $V_{2}$ = x ml = $25 ml \times \frac{0.001 L}{1 ml}$,        $M_{2}$ = 0.650 M

It is known that relation between molarity and volume of two solutions is as follows.

        $M_{1}V_{1}$ = $M_{1}V_{2}$

        $0.10 M \times 0.025 L$ = $0.650 \times x$

                x = 0.00385 L

or,                = 3.85 ml

Since, this volume is closest to 4 ml so, we have to use a 2 ml pipette two times and then we have to put it in a 25 ml volumetric flask.

Hence, calculate the overall concentration as follows.

                    $M_{1}V_{1}$ = $M_{1}V_{2}$

                     $x \times 0.025 L$ = $0.650 M \times 0.004 L$    

                        x = 0.104 M

Therefore, it is about 3.8% error that is lower than the required error.