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Name: Amit S.
Status: student
Grade: 9-12
Country: India
Date: Summer 2009


Question:
Why does petroleum ether have a range of boiling points 35-60 degrees Celsius? Why is it not one constant value?



Replies:
Amit,

Petroleum ether is a horribly misleading name. For starters it is not an ether (R-O-R'), it is a mixture of saturated hydrocarbons (CnH2n+2) taken as a fraction from the distillation of crude oil. So it does not have a fixed boiling point as it is not a pure substance.

It is generally used as it is cheaper than a pure hydrocarbon, but behaves in a predictable way as a solvent or fuel. It is not generally used as a reagent as it is not a pure substance so it would give a mixture of products in a chemical reaction. The exact composition will vary depending on the boiling range you buy and on the source it was extracted from, but can be expected to contain almost entirely alkanes, some straight and some branched.

Best wishes

Tom Collins


First, "petroleum ether" is not an ether. An ether contains ---CH2-O-CH2--- somewhere in its molecular structure. Second, "petroleum ether" is a mixture of hydrocarbons tapped off to have a desired boiling point range during the distillation of hydrocarbons. The hydrocarbons are typically alkanes (no double bonds or ringed substances. So the term "petroleum ether" is misleading. I am guessing but I think the name derives from the boiling range that is similar to diethyl ether, and the term "petroleum" derives from its source.

Vince Calder


Amit,

Petroleum is a mixture of hydrocarbons and the reported boiling point range describe the lowest and highest boiling points of the substances within that mixture.

Greg (Roberto Gregorius)
Canisius College


Petroleum ether is not a single pure compound. It is a mixture of hydrocarbons, which have different boiling points when pure.

Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming


Hi Amit.

Petroleum ether is actually a mixture of hydrocarbons. That is to say, it is a mixture of different length alkanes. An alkane is a molecule that is a chain of carbon atoms. The longer the chain, the more energy it takes to make it boil, and therefore the higher the boiling point. You can find petroleum ether which has a much higher boiling point than the one you describe below, and would therefore have longer hydrocarbon chains.

Hope this helps.

Michelle Weinberger



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