Chapter 30

Determine the concentration of metal ions based on atomic spectroscopy of test and standard solutions. The following data represent a set of calibration standards for \(\mathrm{K}^{+}\)in aqueous solution, measured by flame photometry: Absorbance of standard solutions containing \(\mathrm{K}^{+}\)at up to \(0.5 \mathrm{mmol} \mathrm{L}^{-1}\) $$ \begin{array}{cc} \mathrm{K}^{+} \text {concentration }\left(\mathrm{mmol} \mathrm{L}^{-1}\right) & \text { Absorbance } \\ 0 & 0.000 \\ 0.1 & 0.155 \\ 0.2 & 0.279 \\ 0.3 & 0.391 \\ 0.4 & 0.537 \\ 0.5 & 0.683 \\ \hline \hline \end{array} $$ Draw a calibration curve using the above data and use this to estimate the amount of \(\mathrm{K}^{+}\)in a test sample prepared by digestion of \(0.482 \mathrm{~g}\) of sample in a final volume of \(25 \mathrm{ml}\) of solution, giving an absorbance of \(0.429\) when measured at the same time as the standards shown above. Express your answer in mmol \(\mathrm{K}^{+}\)(g sample) \(^{-1}\), to 3 significant figures.

Determine unknowns from a calibration curve. The following data are for a set of calibration standards of \(\mathrm{Zn}\), measured by atomic absorption spectroscopy. Absorbance measurements for a series of standard solutions containing different amounts of zinc: $$ \begin{array}{cc} \text { Zinc concentration }\left(\mu \mathrm{g} \mathrm{mL}^{-1}\right) & \text { Absorbance } \\ 0 & 0.000 \\ 1 & 0.082 \\ 2 & 0.174 \\ 3 & 0.257 \\ 4 & 0.340 \\ 5 & 0.408 \\ 6 & 0.463 \\ 7 & 0.511 \\ 8 & 0.543 \\ 9 & 0.561 \\ 10 & 0.575 \\ \hline \end{array} $$ Draw a calibration curve by hand using graph paper and estimate the concentration of zinc in the following water samples: (a) an undiluted sample, giving an absorbance of \(0.157 ;\) (b) a 20 -fold dilution, giving an absorbance of \(0.304\) (c) a five-fold dilution, giving an absorbance of \(0.550\) Give your answer to three significant figures in each case.