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Remember, 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 how fast a reaction occurs!

In this experiment, you will break an effervescent tablet into four equal parts. The first, you will put in cold water. The second you will add to cold water while stirring. The third portion will be put in hot water. And the fourth will be crushed before adding it to cold water. In each experiment, you will time how long it takes for the quarter tablet to dissolve.

 

Materials:

  • One "effervescent tablet" such as Alka Seltzer®
  • Four beakers
  • 400 ml. water
  • Hot plate
  • Mortar and pestle
  • Stir rod
  • Graph paper
  • Safety glasses
  • Watch, clock, or stop watch with second hand
 
Safety concerns: icon Be sure to keep all glassware, eye, and chemical safety rules. 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.
 

 

  • Procedure
    1. Wear your safety glasses.
    2. Carefully break your "effervescent tablet" into four equal sized pieces. (They may not be totally equal but do your best to make them so.)
    3. Add 100 ml. water to one beaker.
      • Take a piece of your tablet and place it in the water.
      • Begin to time in seconds as soon as the tablet goes into the water.(Click the link to watch a QuickTime movie of the reaction. Remember to use the back arrow to return to this page.)
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record your data and label it your control sample.
    4. Add 100 ml. of water to a second beaker.
      • Take a piece of your tablet and place it in the water.
      • Begin to time in seconds as soon as the tablet goes into the water.
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record your data.
    5. Add 100 ml. of a water to your third beaker.
      • Heat the water in the beaker (Set the dial on the hot plate to medium and heat for two minutes.)
      • Take a piece of your tablet and place it in the hot water.
      • Begin to time in seconds as soon as the tablet goes into the water.
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record your data.
    6. Add 100 ml. of water to your fourth beaker.
      • Crush the remaining quarter of the tablet and place it in the water.
      • Begin to time in seconds as soon as the tablet goes into the water.
      • Continue to time the experiment until the tablet has completely disappeared.
      • Record your data.
    7. Make a bar graph to compare your data.
  •  

    Data Table:

     
    Control
    Stirred
    Hot
    Crushed
    Time for tablet to disappear:        

     

    Assessment

    1. What 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 variable (cold, hot, stirred, or crushed) caused the effervescent tablet to dissolve the fastest?
      • Which variable caused the effervescent tablet to dissolve the slowest?
    3. What gas do you think was released?
    4. If you had used vinegar instead of water in this experiment, do you think that your results would have been different?

    Review Science safetey 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:

    1. The title of the activity
    2. The URL (Internet address)
    3. Your name.

    Remember that no pictures can be used that show student faces or student names on it. 

    Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 8th grade science core.


    Updated October 24, 2008 by: Glen Westbroek

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