Question

This experiment was a qualitative method of detecting cations. However there are also many quantitative method of testing for cations in solutions. Choose one quantitative method that would allow you to determine the concentration of Cu2+ (one of the cati tration of Cu2+ (one of the cations tested for in this experiment) and provide a description of that method. Cite the source that you used to obtain this information. [10 points]

Answer 1

Dissolve 0.0393 g of pure copper(I1) sulphate pentahydrate in 1 L of water in a graduated flask. Pipette 10.0 mL of this solution (containing about 100 pg Cu) into a beaker, add 5.0 mL of 25 per cent aqueous citric acid solution, render slightly alkaline with dilute ammonia solution and boil off the excess of ammonia; alternatively, adjust to pH 8.5 using a pH meter. Add 15.0mL of 4 per cent EDTA solution and cool to room temperature. Transfer to a separatory funnel, add 10mL of 0.2 per cent aqueous sodium diethyldithiocarbamate solution, and shake for 45 seconds. A yellow-brown colour develops in the solution. Pipette 20 mL of butyl acetate (ethanoate) into the funnel and shake for 30 seconds. The organic layer acquires a yellow colour. Cool, shake for 15 seconds and allow the phases to separate. Remove the lower aqueouslayer; add 20 mL of 5 per cent sulphuric acid (v/v), shake for 15 seconds, cool, and separate the organic phase. Determine the absorbance at 560 nm in 1.0 cm
absorption cells against a blank. Al1 the copper is removed in one extraction.