Question

6. (16 pts.) When you performed (or will perform) the atomic absorption experiment, you performed parallel dilutions (in lieu of serial dilutions) with a Zn2+ standardized solution, and

used your analysis of these dilutions to construct a calibration curve relating the sensitivity of the instrument to the Zn2+ concentration In this problem, you are going to quantify the uncertainty in the concentrations of Zn2+ dilutions obtained from both serial and parallel dilutions and compare the results for the two methods. You have access to a 10.000 mM standardized aqueous Zn2+ solution, an uncalibrated 1.00(1) mL volumetric pipette, an uncalibrated 10.0(1) mL volumetric pipette, and uncalibrated 100.0(2) mL volumetric flasks.

a. (2points) In 50 words or less, explain what is meant by parallel versus serial dilution and how they differ.

b. (4 points) Assume you make a 1:10 dilution from the standardized “stock” solution by using the 10 mL volumetric pipette to transfer 10 mL of the standardized solution to a 100 mL volumetric flask, and then filling the flask to the 100 mL mark with nanopure H2O. Calculate and report the concentration, including uncertainty, of this initial dilution.

c. (4points) In order to make a 1:100 dilution (relative to the concentration of the initial standardized 10 mM solution) from the 1:10 diluted solution produced in the previous question, you would transfer 10 mL of the diluted solution from task b.to a separate volumetric flask, and thenfill to the 100 mL mark with nanopure H2O. Calculate and report the concentration, including uncertainty, of this 1:100 dilution.

d. (4 points) An alternative method for making the 1:100 dilution is to transfer 1 mL of the standardized 10 mM solution to a volumetric flask and then fill to the 100 mL mark with nanopure H2O. Calculate and report the concentration, including uncertainty, of this 1:100 dilution.

e. (2 point) Identify which dilution process represents a serial dilution and which a parallel dilution (considering tasks c. and d.) and state which process yields a 1:100 solution

less uncertainty in the concentration.

Answer 1