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Coal: Classroom Activities

Investigating Types of Coal


Goal

To develop a better understanding of the physical and chemical properties of various types of coal and their energy content.

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Background Information

Coal is a sedimentary rock that consists mostly of combustible material in the form of carbon. Most coal starts out as peat, a porous material that consists of plant materials that have been partly decomposed. If the peat is buried by sediment, it is subjected to compaction and temperature increase, which alter it physically and chemically, to eventually form coal. Increasing time, compaction, and heat result in the formation of coal types with progressively greater percentages of carbon (lignite, bituminous, anthracite). The greater the percentage of carbon in a coal sample, the greater its heat energy value.

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Activity Overview

Students observe the physical properties of peat, lignite, bituminous, and anthracite coal. They record their observations in a table. In a class demonstration, the samples are then burned. Students observe the chemical properties of the forms of coal by examining how they burn when put in an open flame. Students use their observations to rank the samples according to which might contain the most stored energy.

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Materials and Equipment

safety goggles, hand lens, coal sample set (includes peat, lignite, bituminous, and anthracite), tongs, safety gloves, Bunsen burner

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Activity

4 different types of coal
Source: The American Geological Institute, EarthComm: Project-Based Space and Earth System Science, 2nd Edition, Armonk, New York: It's About Time, 2012, pg. 737.

 

  1. Ask students to put on safety goggles.
  2. Have students carefully examine samples of four different types of coal. Encourage them to use a hand lens. Ask students to identify the physical properties of the samples including the following:
    1. evidence of plant origin
    2. hardness
    3. luster (the way light is reflected off the surface of the sample)
    4. cleavage (tendency to split into layers)
    5. any other characteristics
  3. Ask students to record their observations in a data table.

Students may observe the following:
Peat: brownish, softest of the 4 samples, dull luster, visible plant matter
Lignite: brownish-black to black, 2nd softest of the 4 samples, dull luster, some visible plant matter
Bituminous: black, 3rd softest of the 4 samples, more shiny luster, layers and cleavage
Anthracite: black, hardest of all 4 samples, semi-metallic shiny luster, conchoidal fracture

  1. Have students complete the following:
    1. Describe any differences that you observed among the coal samples.
      Answers will vary according to observations made in #3.
    2. How might the samples be related?
      Answers will vary according to observations made in #3.
    3. Order the samples from least compacted to most compacted.
      peat, lignite, bituminous, and anthracite
    4. Which sample do you think contains the most stored energy? Why do you think so?
      Answers will vary. Anthracite contains the most stored energy, whereas lignite contains the least.
    5. The main difference in the formation of the samples is the pressure and temperature of their formation. Which do you think formed at the highest temperature and pressure? Why?
      Anthracite formed at the highest pressure and temperature. Students may recognize this because anthracite is the most compact and hardest of the samples.
    6. Which sample do you think is easiest to burn? Explain your answer.
      Answers will vary.
    7. Which sample do you think contains the most stored energy? Why do you think so?
      Answers will vary.
  2. Tell students that you will be conducting a class demonstration in which you will ignite a small piece of each coal sample. Have them observe the following as they watch the demonstration:
    1. speed of ignition
    2. color of the flame
    3. speed of burning
    4. odor
  3. Ask students to record their observations in a data table.
  4. Using tongs, safety gloves, and goggles, ignite a small piece of each sample of coal over a Bunsen burner. Upon ignition, remove each sample from the flame and allow students to observe how the sample burns.
  5. Ask students to summarize the major differences they observed.
    Students should observe that peat and lignite are ignited more readily and burn faster than bituminous and anthracite. The flame of bituminous and anthracite is smaller and more bluish. Odor depends on other materials in the coal, e.g. sulfur.
  6. Have students review their answers to the questions in step 4. Have their ideas changed? Ask them to explain.
    Answers will vary.

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