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Recall that a chemical change occurs when two substances interact causing one or both to change properties. Variables can change the expected results of experiments. This activity will allow you to experiment with variables and see how they can affect chemical changes!

Materials:

  • One effervescent tablet (such as Alka Seltzer®)
  • Four beakers
  • 50 ml. water
  • 50 ml. each of three other clear liquids (options below):
    • 3% hydrogen peroxide
    • Vinegar
    • Clear soda
    • Vegetable oil
  • Corn syrup
  • Graph paper
  • Safety glasses
  • Watch, clock, or stop watch with second hand
  • Procedure
    1. Carefully break the effervescent tablet into four equal-sized pieces. (They may not be totally equal but do your best to make them so.)
    2. Wear your safety glasses.
    3. Add 50 ml. of water to one beaker.
      • Take a piece of the effervescent tablet and place it in the liquid.
      • Begin to time in seconds as soon as the tablet goes into the liquid.(Drag your mouse over the link to watch a QuickTime movie of the reaction. It will open in a new browser window. Remember to close the window when you finish watching the movie to return to this page.)
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record the data.
    4. Add 50 ml. of a clear liquid to the second beaker.
      • Take a piece of the effervescent tablet and place it in the liquid.
      • Begin to time in seconds as soon as the tablet goes into the liquid.
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record the data.
    5. Add 50 ml. of a different clear liquid to the third beaker.
      • Take a piece of the efferevescent tablet and place it in the liquid.
      • Begin to time in seconds as soon as the tablet goes into the liquid.
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record the data.
    6. Add 50 ml. of a different clear substance to the fourth beaker.
      • Take a piece of the effervescent tablet and place it in the liquid.
      • Begin to time in seconds as soon as the tablet goes into the liquid.
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record the data.
    7. Make a bar graph to compare the data.
    		•
    Safety concerns: icon Be sure to follow all glassware, eye, and chemical safety rules that are specified by your teacher and in all general laboratory experiences. DO NOT allow your beaker to be covered or stoppered. Make sure that you protect your body and clothing from the reactions. As with all science lab activities, the most important safety rule is to follow all teacher directions.

     

    Data Table:

     
    Water
    Liquid 1 __________
    Liquid 2 __________
    Liquid 3 __________
    Time for tablet to disappear:        

     

    Other possible variables to test:

    You might consider either of the following:

    • Changing the size of the effervescent tablet by breaking it into smaller pieces or crushing it to increase the surface area.
    • Use different liquid temperatures (cool, room temperature, and warm.)

     

    Assessment

    1. Which type of change (physical or chemical) did this experiment show?
      • What evidence did you observe that supports this answer?
    2. Based on the data in your graph:
      • Which liquid helps dissolve effervescent tablets the fastest?
      • Which liquid helps dissolve effervescent tablets the slowest?
    3. What do you think the gas was which was given off in the bubbles?
    4. What happened to the solid tablet?

    Review science lab safety rules here.

    Get the plug-ins: Get Adobe Acrobat Reader , and Get Quicktime Player (The QuickTime plug-in is needed to play sounds and movies correctly.)

    Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information: the title of the activity, the URL (Internet address), and your name. Remember that no pictures can be used which show any student faces or has a student name on it.

    Updated August 13, 2005 by: Glen Westbroek

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