Test Bank - Atomic Emission Spectroscopy Ch9

EXERCISE 9.9: In the analysis of sea water for gold content, a series of calibration standards were prepared using 4% HCl in deionized water as the diluent and then measured using ICP-AES after setting the response to zero with neat 4% HCl. A 10.00 mL aliquot of the sea water was acidified by adding 1.25 mL of concentrated (36.0%) HCl and then measured using the same method, yielding a response of 1,433 (arbitrary units).

1. What was the percentage of HCl in the treated sea water sample?
2. Calculate the concentration of the gold in the original sea water sample.
3. Calculate the standard deviation of the calculated concentration.

1. Determine the 95% confidence interval for the measurement.

1. Do you see any potential problems with this method as described? Explain. What would you do differently?

EXERCISE 9.10: Chromium is sometimes measured in abnormal concentrations near heavily traveled roads due to its presence in petroleum products (e.g., gasoline, oil, tires).

An LIBS system was mounted on the back of a truck to sample roadside soils along Highway 73 in Texas. Prior to departure, a standard sample of 10.00 mg∙kg^-1 Cr in clean soil was sampled using the truck-mounted system, giving a mean reading of 17.32 ± 0.13 mA for ten readings. The truck then sampled roadside soil along the highway at six locations. The locations given in the table are GPS longitude/latitude designations; you can use “loc: N29.826° W94.368°” in Google to find that location on a map.

(a) Estimate the concentration of chromium in the soil at each location.

(b) Is the Cr in the soil at the third location (N29.826°, W94.250°) significantly (statistically speaking) above the standard sample?

(c) Rationalize the trend(s) you see in the data.

(d) How accurate would you say the data are? How many significant figures do you believe you can reasonably assign to the calculated concentrations? Explain your rationale.

(e) What would you do to achieve greater accuracy in the concentration of Cr in roadside soils?

EXERCISE 9.11: What is the ratio of excited state versus ground state atoms in an 8,000K plasma, assuming the degeneracy of states is 1? (Hint: See Equation 4.15.)

EXERCISE 9.13: One of the advantages atomic spectroscopy has over molecular spectroscopy is the very narrow bandwidth of the observed transition. However the bandwidth is not infinitely narrow. In fact the Heisenberg Uncertainty principle states that . What is the theoretical minimum bandwidth for the mercury 546.074 nm line if the lifetime of the transition (Δt) = 2 ns? Note: This calculation requires differentiation. Attempt this problem on your own, but refer to Chapter 7, Section 7.3 if you are struggling with it.