Many combustible fuels have been given octane ratings , numbers that determine h
ID: 780105 • Letter: M
Question
Many combustible fuels have been given octane ratings, numbers that determine how suitable the fuel is as a gasoline for automobiles. Regular unleaded gasoline has an octane rating of 89. Octane ratings are reported in tables for reference:
Predict the product and draw it in the cis conformation.
One of these products exhibits optical isomerism. Draw this product. Assume mono substitution.
Fuel additive Octane rating heptane 0 hexane 25 pentane 62 isooctane 100 benzene 106 ethanol 108 p-xylene 116 toluene 118Explanation / Answer
To "determine the octane ratings of the constituent fuels", you have to find the octane ratings of pentane and ethanol. According to the table, it would be 62 for pentane and 108 for ethanol. Then, you "multiply each octane rating by the fraction of the final gasoline represented by that fuel". 35.0% of the mixture is ethanol, which means that 65.0% must be pentane. I'll use decimals, because I think they're easier, but you could use fractions too here: multiply the octane rating of ethanol (108) by its decimal (0.35) and the octane rating of pentane (62) by its decimal (0.65). So, you have (108)(0.35) = 37.8 for ethanol and (62)(0.65) = 40.3 for pentane. Adding the two together, you get 78.1 for the octane rating. It's pretty much just a weighted average.
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