To Accompany Brown & Foote Organic Chemistry
3rd Ed.
Chapter 9. Alcohols & Thiols
Read the following article:
New
weapon introduced against drunken driving
by Associated Press (USA Today, August 28, 2002)
Read
the instructor's editorial comments below once through before following the
links in this section intended to help you explore the topic further:
Ethanol effects body functions including response time and judgement, therefore state legislation has been enacted that regulates driving under the influence of alcohol. The amount of alcohol in your system is detected by measuring the blood alcohol concentration (BAC). Since it is unlikely that an officer of the law would be taking a blood sample at the scene of an incident, manufacturers have developed other testing methods that measure the alcohol that is in your breath. This is not a direct measure of the BAC, therefore the method must be tested to determine the blood level that correlates to each level in the breath. The instrument needs to be calibrated so that the measurement reflects a reasonably accurate determination of the BAC. These instruments, like the Breathalyzer, were made available to law enforcement agencies. Currently, many products are now available for individuals to test their own BAC so that they can make an informed decision before driving a vehicle after drinking. These products range from electronic instruments like the key-ring breathalyzer to simple chemical color tests either packaged as crystals (Alcohol Check) or embedded on a test strip (Guardian Angel Personal Alcohol Test).
Write a 2 to 10 sentence paragraph for each.
1. The original breathalyzers worked by converting alcohol to acetaldehyde, but this does not result in a color change. The reaction involves a chromium compound such as potassium dichromate, which does change colors as the chromium oxidation state changes. Using the reaction of ethanol to acetaldehyde below, determine whether the ethanol is oxidized or reduced and explain your reasoning.
2. Using an interactive Periodic Table, find the possible oxidation states for chromium. Potassium dichromate (K2Cr2O7) are bright orange-red crystals. Determine the oxidation state for the chromium. When potassium dichromate is used in the breathalyzer reaction is the chromium reduced or oxidized?
3. Alcohol Check is a vial of yellow crystals that change to a vibrant blue after reacting with alcohol. Chromium has been classified as toxic, thus it has been replaced in the newer products. A compound that would act similarly is vanadium pentoxide, which is yellow crystal. Vanadium trioxide is a black powder, but is converted to indigo-blue V2O4 crystals upon exposure to air. Determine the oxidation states for the vanadium in each of these compounds and check to see if these are common oxidation states of vanadium on the Periodic Table site.
4. The Guardian Angel site states that the test strips are accurate, however several compounds will interfere with the test strip reaction. Some of the substances that interfer are antioxidants, thiols, carboxylic acids, and peroxides. Provide a reasonable explanation why these functional groups might interfere with the test for alcohol.
Dr. Easter's Course Information