Potassium can be determined by flame emission spectrometry (flame photometry) using a lithium internal standard. The following data were obtained for standard solutions of KCl and an unknown containing a constant, known amount of LiCl as the internal standard. All the intensities were corrected for background by subtracting the intensity of a blank.
cK, ppm | Intensity of K Emission | Intensity of Li Emission |
1 | 10 | 10 |
2 | 15.3 | 7.5 |
5 | 34.7 | 6.8 |
7.5 | 65.2 | 8.5 |
10 | 95.8 | 10 |
20 | 110.2 | 5.8 |
Unknown | 47.3 | 9.1 |
(a) Plot the K emission intensity vs. the concentration of K, and determine the linearity from the regression statistics.
(b) Plot the ratio of the K intensity to the Li intensity vs. the concentration of K, and compare the resulting linearity to that in part (a). Why does the internal standard improve linearity?
*(c) Calculate the concentration of K in the unknown.
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