Two solutions used in atomic absorption measurements with an acetylene/air flame
ID: 830878 • Letter: T
Question
Two solutions used in atomic absorption measurements with an acetylene/air flame contain equal concentrations of calcium. For each of the conditions given below, indicate which of the two solutions will yield the higher absorbance value at 422.7 nm (a line in the atomic absorption spectrum of Ca). Explain your choices.
a. The flow rate of air is greater when solution 1 is analyzed than when solution 2 is analyzed.
b. Solution 2 was prepared using ethanol as the solvent, while solution 1 is an aqueous solution.
c. Solution 2 contains 500 ?g/mL of KCl in addition to the Ca.
Explanation / Answer
a. The flow rate of air is greater when solution 1 is analyzed than when solution 2 is analyzed.
by increasing the flow rate of air, molar ratio of fuel decreases, combustion becomes less efficient hence decreasing the overall temperature of the flame which results in lesser excitation of atoms. hence absorbance will also decrease in Case of solution 1 as compared to 2.
b. Solution 2 was prepared using ethanol as the solvent, while solution 1 is an aqueous solution.
Solution 2 will have greater absorbance absorbance as compared to 1. because ethanol is easily aspirated as compared to water due to less surface tension. hence ethanol as a solvent not only improves aspiration but also excitation at higher temperature because it is itself a combustionable material.
c. Solution 2 contains 500 ?g/mL of KCl in addition to the Ca.
the presence of spectator ions in solution will have a negative effect on the absorption because of light scattering or absorption by these ions. they increse the viscosity and the surface tension of solution so difficult to aspirate. hence solution 2 will have less absorbance as compared to 1.
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