We will provide a standard solution of 0.100 M NaCl and a solution of 20-fold diluted tonic water (the unknown) for your use. The whole class will use these reagents and we will compare all results. Design a range of five volumes of the NaCl standard solution that you will spike into equal aliquots of the unknown . First decide what volume of tonic water unknown to add to each 25-mL volumetric flask. Try to have the third out of five spiked solutions produce approximately double the absorbance of the diluted tonic water. We found that the spectrometer would not register a reliable absorbance much greater than 0.5, so try not to exceed this. You may have to dilute the 0.100 M NaCl stock solution before making your standard additions.