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Cola and Cola light contains ions of phosphoric and citric acid. So they should have have a high electric conductivity. During distillation these ions are separated from the water. In the following experiment the electric conductivity of different water samples (Photo 1 - 4) is measured.
Material
Tray, digital AC/DC multimeter with a range between 20 and 200 mA  AC,  3 cables with crocodile clips,  AC/AC adaptor ("Netzgerät") ( Conrad order Nr. 510004-55, price 5 €), wellplate 6 (WP6) with lids, 2 pins, 4 plastic barrel pipettes,  drinking straw spatula, stale samples of Cola, Cola light, Cola distillate, sodium sulfate ("Glauber salt").
Experiment
1. Transfer 3 mL of the following solutions into wells 1 - 4 of WP6: Cola distillate (1), Cola (2), Cola light  (3 und 4).
2. Connect the input "COM" of the AC/AC multimeter with the AC/AC adaptor and its output with one of the pins.
3. Connect the input "Amp" of the  AC/AC multimeter with the second pin.  
4. Set the multimeter to 20 mA DC.
5. Photo 1: Close the circuit starting with well 1 by dipping the two pins into distilled water.
6. Write down the current.
7. Repeat 5 and 6 with well 2 containing Cola (Photo 2) and mit Cola light (Photo 3). 
8. Photo 4: Add a spatula tip of Glauber salt (sodium sulfate to Cola light in well 4, stirr and repeat the measurement.
Observations
see Figs. 1 - 4
Explanation
The current depends on the concentration of ions dissolved in the liquid. Distilled water or Cola-distillate (Fig. 1) have the lowest concentration, Cola with dissoved Glauber salt (Fig. 4) the highest.
The higher conductivity of Cola light is due to the fact that it contains not only ions of phosphoric acid but also of citric acid.