The alcohol digested by a person is not chemically modified in the bloodstream. As blood passes through the lungs, some of the alcohol molecules is immersed in air bags lung (alveoli), because of the alcohol in the blood is evaporated due to its high volatility. The alcohol concentration in the alveolar air is related to the concentration of alcohol in the blood.
Because alcohol exhaled in breathing can be determined by various mechanisms and through an established relation the concentration of alcohol in blood can be determined . This allows to know the relation of alcohol in blood without having a sample of it, but simply with breathing and get it.
The alcohol in breath is examined using a device called a breath analyzer.
The chemical operation of these devices is explained by a redox reaction.
A driver's breath sample is introduced into the analyzer where it reacts with potassium dichromate in an acidic medium.
The reaction is represented by the following equation:
In this reaction, ethanol is oxidized to acetic acid and chromium (IV) ion dichromate, reddish-orange ion is reduced to chromium (III), green. The intensity of the color change is directly related to the level of alcohol in exhaled air and therefore also in the blood.
Silver nitrate used is a catalyst which causes the reaction to go faster.
The theme redox reactions it would work only in the second year of high school where the student already has got various skills needed for the construction of this new knowledge.
I leave an activity where they can work the above.
Experimental Activity
Redox reactions
Previous activities:
> Find out about the alcohol content of different drinks usually consumed.
> Make calculations of the shots required to prepare 100ml of solution at different concentrations.
Objective:
> Explain the operation of the spirometer through redox reactions.
> Observe the color change that occurs in response to varying concentrations of alcohol
Rationale:
> Redox reactions
> Oxidizing agents, reducing
> Alcohol
> Limiting reagent
Materials:
> test tubes
> Tweezers
> Bohemian glass
> Flask
> Burner
> Pipette
> Ethanol 95% v / v
> Potassium dichromate 5% m / v
> Distilled water
Procedure:
> Prepare 100 ml of an ethanol solution of 5% v / v, 10% v / v 20% v / v respectively.
> Place in 3 test tubes 10 ml of potassium dichromate 5% m / v
> Place in 3 tubes the same volume of 0.5 ml of ethanol solution with different concentrations.
> Place the tubes in water bath for a few minutes and observe the changes
This practice is intended students to link the themes from a corpuscular view with macro phenomena. The concentrations of ethanol previously reacted are linked with different graduations of the most common beverages.
This is a practice that is not a quantitative but rather qualitative.
bibliography:
> Sanmarti, Neus "The design of teaching units" Autonomous University of Barcelona
> Laborde, Gustavo "designing lesson plans" and "Planning in Education"
> Atkins "principles of chemistry"
They were also used to support materials during the course of General Chemistry I
I found your post very interesting it, alcoholemio control is increasingly common (something I think is very good) and learn is very good as you can get through a breath apparatus much alcohol is in your blood.
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