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Recall that a chemical reaction has reactants which enter into the reaction. It also has products which are the substances that result from the reaction. Based on this information, you will be given the opportunity to prove that the amount of matter that enters the reaction is the same as the amount of matter that is found after the reaction.

Be careful to follow all directions below so you are able to prove this fact! The mass that enters into a chemical reaction is equal to the mass that results from a chemical reaction! This reaction will allow you to observe color changes that result from a chemical reaction.

 

Materials:

  • One small head of Purple cabbage
  • Knife or kitchen grater
  • Five clear beakers
  • Clear liquids (options: vinegar, sugar water, baking soda in water, soda, salt water, and water)
  • Balance scale
  • Graduated cylinder
 
Safety concerns: icon Be sure to keep all glassware,eye, and chemical safety rules. As with all science lab activities, the most important safety rule is to follow all teacher directions.
 

Procedure

  1. Cut or grate the purple cabbage into a large bowl.
    • Add distilled water until the cabbage is completely covered.
    • Allow this mixture to sit without being disrupted for one hour.
  2. Measure and record the mass of a beaker
    • Add 50ml of one clear liquid to the beaker.
    • Measure and record the mass of the beaker again.
    • Follow the same procedure for each of the other four beakers.
  3. Measure mass of your graduated cylinder
    • 15 ml of cabbage juice into a graduate cylinder.
    • Measure the record the mass of the cabbage juice.
    • Subtract the mass of the graduated cylinder to obtain the mass of only the cabbage juice.
    • Add the mass of the beaker with the liquid to the mass of the cabbage juice.
  4. Pour the 15 ml of cabbage juice to a beaker containing one of your clear solutions.
    • Make observations of color change.
    • Measure and record the mass of the beaker again.
  5. Continue until you have completed the process for all five solutions.
 

Data:

  Sample1 Samplew2 Sample3 Sampler4 Sample5
Clear liquid being tested          
Measured mass of beaker          
Measured mass of beaker and 50 ml. clear liquid          
Mass of clear liquid minus mass of beaker          
Measured mass of graduated cylinder          
Measured mass of graduated cylinder and 15 ml. cabbage water          
Measured mass of cabbage water minus mass of graduated cylinder          
Mass of clear liquid added with mass of cabbage water (done before adding in the experiment)          

Measured mass of beaker, clear liquid, and cabbage water after experiment

         
Measured mass of clear liquid and cabbage water minus mass of beaker          
 

Analysis:

  1. What kind of change was observed (chemical or physical)?
  2. How did the mass of each clear liquid added to the mass of the 15 ml. cabbage juice compare to the actual measured mass when they were combined?
  3. What evidences of change did you observe in the experiment?
 

Extension:

The cabbage juice acts as an indicator for acids and bases. Strong bases will turn it yellow, mild bases will turn it green, weak will turn it blue. Strong acid turn it red, more mild acids turn it pink. Based on the experiment observations, which of your liquids were acids and which were bases? Were any strong acids or strong bases?

Review Science safetey rules here.

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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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