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Determining Molecular Formulas

Calculating the kind and number of atoms of each element in a molecule

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Different Wells, Different Oil

Different Wells, Different Oil

Credit: Drunken Sailor mn
Source: https://commons.wikimedia.org/wiki/File:TorbenSpirit-SingaporeAnchorage-20050906.jpg
License: CC BY-NC 3.0

The oil slick was observed and reported. Measures were taken to contain and clean up the contaminants. Questions of liability quickly came to the fore – was the oil spill from a passing tanker or from off-shore drilling in the region? Detailed analysis of the oil from both sources was carried out. The two oil chemical profiles were different, so it was an easy matter to identify the source of the contamination. It turned out that there was a leak in an underground pump from the drilling site. Repairs were quickly initiated, along with clean-up, and the problem was eventually solved.

Why It Matters

  • Oil is a complex mixture of materials, varying in composition from one site to another. An elemental analysis gives us the empirical formula, with the elemental composition being carbon (93-97%), hydrogen (10-14%), and small amounts of nitrogen, oxygen, and sulfur. While we could write an empirical formula for oil, it would not be very useful in terms of composition.
  • Molecular analysis of petroleum shows a variable, but complex, mixture of materials. There are four major organic (carbon-containing) fractions to petroleum: alkanes (straight- and branched chain hydrocarbons), naphthalenes (cyclic compounds containing two or more benzene rings), aromatics (benzene ring compounds), and asphaltenes (long-chain hydrocarbons).
  • A detailed molecular analysis of petroleum would show the presence of over a thousand different compounds. Many of these are isomers of one another, some are gases, and some boil at temperatures in excess of 400°C. During the useful lifetime of an individual oil well, the detailed composition of the petroleum may vary significantly.
  • Watch a video about the 2010 Gulf of Mexico oil spill at the link below:


Show What You Know

Use the links below to learn more about oil analysis. Then answer the following questions.

  1.  What forms of sulfur are found in petroleum?
  2.  What country provides the largest source of petroleum to the U.S.?
  3.  What is the most profitable petroleum composition for use as a fuel source?
  4.  What is the major use for kerosene?
  5.  What is the major component of natural gas?

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Image Attributions

  1. [1]^ Credit: Drunken Sailor mn; Source: https://commons.wikimedia.org/wiki/File:TorbenSpirit-SingaporeAnchorage-20050906.jpg; License: CC BY-NC 3.0

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