Question

Which of the procedures, if either, is more accurate when making a 1/501/50 dilution of a solution? Transfer 1 mL1 mL with a pipet into a 50-mL50-mL volumetric flask. Transfer 20 mL20 mL with a pipet into a 1-L1-L volumetric flask. Both procedures have the same accuracy. How can the accuracy of either procedure be improved?

Answer 1

Full question:

First of all, bear in mind that this question is incomplete. Here is the full question:

• Which of the procedures, if either, is more accurate when making a 1/50 dilution of a solution?

a) Transfer 1 mL with a pipet into a 50-mL volumetric flask.

b) Transfer 20 mL with a pipet into a 1-L volumetric flask.

c) Both procedures have the same accuracy.

• How can the accuracy of either procedure be improved?

a) Use an Erlenmeyer flask instead of a volumetric flask.

b) Use a graduated cylinder instead of a pipet for the transfer.

c) Calibrate each piece of glassware.

d) Instead of using a 1/50 dilution to make the solution, weigh out the material on a balance and transfer ir directly to the volumetric flask.

Answer:

1) c) Both procedures have the same accuracy.

2) c) Calibrate each piece of glassware.

Explanation:

1) Given that the 1/50 relation is maintained whether we pour 1 mL into a 50-mL volumetric flask or we transfer 20 mL with a pipet into a 1-L volumetric flask, both procedures have the same accuracy (because in both procedures we are using volumetric glassware).

When we want the most exact result possible, we need to calibrate the volumetric glassware used (bear in mind that the only volumetric glassware is the buret, the volumetric flask, the micropipet and the pipet). This is usually done measuring the mass of water poured by the recipient or contained in it, and using the density of that liquid to convert mass into volume. In this way is possible, for example, to determine that a pipet poured 10.016 mL and not 10.000 mL.