Reagan is doing an atomic absorption experiment that requires a set of zinc standards in the 0.4- 1.6 ppm range. A 1000 ppm Zn solution was prepared by dissolving the necessary amount of solid Zn(NO3)2 in water. The standards can be prepared by diluting the 1000 ppm Zn solution. Table 1 shows one possible set of serial dilutions (stepwise dilution of a solution) that Reagan could perform to make the necessary standards. Solution A was prepared by diluting 5.00 ml of the 1000 ppm Zn standard to 50.00 ml. Solutions C-E are called "calibration standards" because they will be used to calibrate the atomic absorption spectrometer. Table 1: Dilutions of Zinc Solutions Solution Zinc Solution Volume Diluted Concentration used volume Solution concentration Solution concentration (ppm Zn) (mL) (mL) (ppm Zn) A 1000 5.00 50.00 1.00×10² (ppm Zn(NO3)2) 2.90×10² Solution concentration (M Zn(NO3)2 Solution concentration (M Zn) 1.53×10-3 1.53×10-3 100.00 B Solution A 5.00 100.00 5.00 14.5 7.65 x 105 7.65 × 10-5 C Solution B 5.00 50.00 0.50 1.45 7.65×10-6 7.65x10-b D Solution B 10.00 50.00 1.000 2.90 1.53x10 5 1.53 x 10-5 E Solution B 25.00 100.00 1.25 3.62 1.91 x 10-5 1.911×10-5
Reagan is doing an atomic absorption experiment that requires a set of zinc standards in the 0.4-1.6 ppm range. A 1000 ppm Zn solution was prepared by dissolving the necessary amount of solid Zn(NO3)2 in water. The standards can be prepared by diluting the 1000 ppm Zn solution. Table 1 shows one possible set of serial dilutions (stepwise dilution of a solution) that Reagan could perform to make the necessary standards. Solution A was prepared by diluting 5.00 ml of the 1000 ppm Zn standard to 50.00 ml. Solutions C-E are called "calibration standards" because they will be used to calibrate the atomic absorption spectrometer.
a. Compare the solution concentrations expressed as ppm Zn and ppm Zn(NO3)2. Compare the concentrations expressed as M Zn and M Zn(NO3)2
- Which units allow easy conversion between chemical species (e.g. Zn and Zn(NO3)2)?
- Which units express concentrations in numbers with easily expressed magnitudes?
- Suppose you have an analyte for which you don't know the molar mass. Which concentration units would you use?
b. Although only 50 ml of each calibration standard (Solutions C-E) are needed for the experiment. Reagan made 100 ml of Solution E. Give a rationale for this decision.
c. Suppose Reagan made an error in preparing Solution A and ended up 1,,vith a 100.5 ppm Zn solution. What is the impact of this error on Solutions B-E?
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