Question

Using a 10 mL burette and a 100 mL volumetric flask you will prepare, in the lab, standard solutions of ∼ 2, 4, 6, 8 and 10 ppm in Ca2+ from the ∼ 100 ppm standard. You will, of course, need to know these concentrations as precisely as possible. Suppose you have a standard solution which is 99.709 ppm in Ca2+ and 100.790 ppm in Na+. Using the 10 mL burette, you deliver 8.03 mL of this standard solution into a 100.00 mL volumetric flask and dilute it to the mark. What is the concentration (in ppm) of Ca2+ in the new standard, thus prepared?

A 9.99 mL aliquot of the above diluted solution is further diluted, to the mark, in another 100.00 mL volumetric flask. What is the final concentration (in ppm) of Na+ in this new standard?

Answer 1

Ans:

99.709ppm * 4.05/100 = 4.0382 ppm Ca2+.
100.790 ppm * 4.05/100 = 4.082 ppm Na+.

Roughly 4 ppm in both cases.
2/4 * 4.05 mL = 2.025 mL.
6/4 * 4.05 mL = 6.075 mL.
8/4 * 4.05 mL = 8.100 mL.
10/4 * 4.05 mL = 10.125 mL.

Use the 10 mL burette and
make up to the 100 mL mark.
This will give you rough ppm
from which you may work out
the PRECISE ppm of Ca2+ & Na+.

100.790 ppm * 0.0405 = 4.082 ppm.  

the concentration (in ppm) of Ca2+ in the new standard, thus prepared is 4.082/2 = 2.041 ppm

Final concentration new standard =
4.082 ppm * 0.0999 = 0.40779 ppm Na+.