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Law of Multiple Proportions

Elements combine in the ratio of small whole numbers.

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Earth Tones

Earth Tones

Credit: John Dyhouse
Source: http://www.flickr.com/photos/shadfan66/4045455507/
License: CC BY-NC 3.0

The rich browns that Caravaggio and other artists used included the pigment known as burnt sienna. This material is a mixture of iron oxide and manganese oxide. One of the earliest known pigments used in art, it has been found in many cave paintings (the earliest examples of human art).

News You Can Use

  • There are three known iron oxides: wüstite (FeO) found in meteorites and native iron; magnetite (often written as Fe3O4, but actually a mixture of FeO and Fe2O3) one of the most magnetic minerals, and iron (III) oxide (Fe2O3) sometimes known as hematite. Iron (III) oxide is the form of iron that is mined and refined in the steel industry. This oxide is the major component of rust.
  • Iron oxide pigments can provide a wide palette for a variety of painting approaches. These oxides are non-toxic and do not bleed when used on many surfaces. Because they are water-resistant and little affected by exposure to light, the pigments can provide interesting color choices for outside decoration. Concrete, paint, tiles, and rubber use iron oxides to bring color to the materials.
  • Thermite is a mixture of aluminum powder and iron oxide. When heated to ignition, a highly exothermic reaction occurs, producing a temperature in the range of up to 2500°C. This material can be used for welding underwater since it has its own oxygen supply.
  • Credit: Vestman
    Source: http://www.flickr.com/photos/vestman/3543852568/
    License: CC BY-NC 3.0

    Thermite can be used to cut through thick metal objects [Figure2]


  • Iron is a significant component of the hemoglobin molecule in red blood cells. Molecular oxygen will attach to the iron in hemoglobin and be transported to the cells. The oxygen is released from the iron and enters the cell for use in energy metabolism.
  • Watch a video dealing with the thermite reaction at the link below:


Show What You Know

Use the links below to learn more about iron oxides. Then answer the following questions.

  1. What are two common pigments made from iron oxides?
  2. Why is iron oxide used in the cosmetics industry?
  3. What is the chemical form of the iron at the end of the thermite reaction?
  4. What is one industrial use for thermite?
  5. What is the form of iron in hemoglobin?

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Image Attributions

  1. [1]^ Credit: John Dyhouse; Source: http://www.flickr.com/photos/shadfan66/4045455507/; License: CC BY-NC 3.0
  2. [2]^ Credit: Vestman; Source: http://www.flickr.com/photos/vestman/3543852568/; License: CC BY-NC 3.0

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