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1. a. In order listed: -4, -2, 0, +2, +4.
b. & c. They are in order in the question.
2. First consider the three hydrocarbons. The C atoms have oxidation numbers: -3, -2, -1 as listed. Thus, again, they are in order of increasing oxidation state as listed. This corresponds to the loss of 2 H as you go through the list.
What about the ethanol? The average for the 2 C atoms is now -2. Note that this is the same as for the ethene. One can make ethanol from ethene by adding H-OH. Since this reaction adds both two H and one O, there is no change in the overall oxidation state.
For more on redox... See the page on Balancing organic redox reactions. There are various ways to balance redox equations, and the ones you learn in general chem are sometimes not convenient with redox equations involving organic chemicals, or other complex chemicals. This page focuses on an approach that is especially suitable with organic chemicals: emphasizing H and O atoms. Thus it uses the material from this quiz in the context of balancing equations.
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Last update: September 15, 2011