Passage VI
Eating chips of lead-based paint is a cause of lead poisoning in children. According to the law, paint is considered lead-based if the lead content exceeds 0.5% by weight. Atomic-absorption spectroscopy (AAS) is used to determine the lead content of paint. Samples containing lead in solution are vaporized in a flame, and light of a single wavelength characteristic of lead is shone through the flame. The absorbance measures the amount of light absorbed by the lead in the flame. The following experiments were done using AAS.
Experiment 1
Solutions with known concentrations of lead were prepared and their absorbances were measured (see Figure 1).
Experiment 2
Paint chips were collected from interior walls and exterior walls and from outdoor furniture at House A. built in 1945. The paint chips from a given location were powdered. Then 100 mg samples of the powder were treated with nitric acid and heated for at least 30 minutes to convert all of the lead to soluble lead nitrate. The solutions were evaporated to a dry powder, then dissolved in hydrochloric acid and diluted to 100 mL with H2O. The absorbances were treasured and the lead concentrations were determined using the data in Figure 1. The % lead (average weight percent of lead in the paint) at the location was then calculated. The same analysis was performed at House B, built in 1990 (see Table 1).
30. If, in Experiment 1, an additional solution with a lead concentration of 0.14 mg/mL had been analyzed by AAS, the absorbance of this solution would most likely have been closest to:
Your Answer is
Correct Answer is H
Explanation
Put value questions. Looking at the figure, it is speculated that when the abscissa is 0.14, the ordinate is about 1.0 (you can extend the line in the figure to see that when the abscissa reaches 0.14, the ordinate cannot reach 1.10)