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In: Chemistry

What is the purpose of rinsing platinum electrodes with acetone or ethyl alcohol?

What is the purpose of rinsing platinum electrodes with acetone or ethyl alcohol?

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Expert Solution

When users exhale into a breathalyzer, traces of ethanol react with sulfuric acid and potassium dichromate and are then oxidized into chromium sulfate and acetic acid. The silver nitrate in the vial calatyses this chemical reaction:

2 K2Cr2O7 [Potassium dichromate] + 3 CH3CH2OH [Ethyl alcohol] + 8 H2SO4 [Sulfuric acid] + 2 Cr2(SO4)3 [Chromium sulfate Green]+ 2 K2SO4 [Potassium sulfate] + 3CH3COOH [Acetic acid]+ 11 H2O

A photocell system can then be applied to compare the amount of unreacted potassium dichromate left in the vial to the amount of the same chemical used to oxidize ethanol, which will provide a measurement of alcohol content from a sample of breath. The photocell system bases its measurement of alcohol content on the absorption of light by the potassium dichromate. The amount of light absorbed by this chemical will be proportional to the amount of alcohol in the sample cell.

A comparison is then made between the reference sample in the breathalyzer and the suspect sample which generates an electrical current that moves a needle on an indicator meter. One of the main problems with this test is that it consumes the chemicals in the reaction vessel, which means that there is a constant need to calibrate the device and replenish it with the right amount of chemicals to oxidize ethanol in order to provide an accurate reading of alcohol concentration.

queen_honey_blossom answered 8 months ago
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