Lab_3_corrected - Fall 2007 Chemistry 300 Cornell...

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Unformatted text preview: Fall 2007 Chemistry 300 Cornell University Lab 3 Determination of the Quinine Content of Tonic Water I. INTRODUCTION The goal of this two-week lab is to measure the quinine content of different brands of tonic water. II. MATERIALS AND METHODS You will need First day Equipment * analytical balance * fluorimeter Glassware * volumetric pipets: 1, 2, 5, 10, and 25 mL * Pasteur pipets: two * volumetric flasks: two 100 mL * storage vials w/ screw caps: eight Chemicals * quinine * 0.05 M sulfuric acid Second day Equipment * fluorimeter Misc * Ring and ring stand Glassware * volumetric pipets: 2 and 25 mL * volumetric flasks: two 100 mL * storage vial w/ screw caps: eight * separatory funnel: 125 mL * graduated cylinder: two 100 mL * beakers: two 100 mL * Pasteur pipet: one Chemicals * 0.05 M sulfuric acid * 1.5 M sodium hydroxide * methylene chloride Materials * tonic water (degassed) Before coming to lab, you should read the sections in Harveys book covering separations (7F.5, the introduc- tion to 7G, 7G.1, and 7G.2) and fluorescence (10A, 10B, 10G.2, 10G.3, and 10G.4). In this experiment you will use fluorescence to deter- mine the amount of quinine present in commercially- available tonic water. A Turner Designs TD-700 fluo- rimeter is used, with a 310-390 nm lamp, a 300-400 nm excitation filter, a 410-600 nm emission filter, and a pho- tomultiplier tube (PMT) detector. A set of standard quinine solutions is prepared as a calibration curve. You will be instructed to prepare con- centrations that fall within within the linear range of the fluorimeter. The quinine is dissolved in sulfuric acid. This dissolution will convert quinine to its acidified form, which is soluble in aqueous solutions. The basic form of quinine is not soluble in water, but is soluble in methy- lene chloride. The chloride ion quenches the fluorescence of quinine. You therefore cannot measure accurately the fluores- cence of quinine in tonic water directly because tonic water contains a high concentration of the chloride ion. The approach we will take is to extract the quinine into methylene chloride and then back again into deion- ized water where we can measure its fluorescence in the absence of the chloride interferant. To accomplish this extraction you will add base and methylene chloride to the tonic water. This addition will convert the quinine to its basic form and transfer it to the methylene chloride layer, leaving inorganic ions behind in the aqueous layer. Adding acid will convert the quinine back into its acidified form, making it water-soluble again so it can be used to prepare solutions. On the first day of lab, your teaching assistant will demonstrate how to 1. use the fluorimeter....
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Lab_3_corrected - Fall 2007 Chemistry 300 Cornell...

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