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The Movement of Liquid Molecules

Suggested Grades

3+

Objective

Students will observe food colouring being diluted in hot, room temperature, and cold water. Through this activity they will be able to visualize and better understand the concept of the constant motion of molecules.

Materials

  • three clear glasses
  • hot, room temperature, and cold water
  • food colouring
  • stop watch

Method

  • Explain to students that everything is made out of molecules and that some objects' molecules move faster than others.
  • Fill a clear glass with some room temperature water. Ask students to predict how long (# of seconds, minutes) they think it will take for all the water in the glass to change colour if you add a few drops of food colouring to it.
  • Add a few drops of food colouring to the water and with a stop watch time how long it takes for the water to completely change colour. Record the time.
  • Once that is complete, pour hot water into a glass. Ask students to predict whether it will change colour faster or slower than the room temperature water.
  • Add a few drops of food colouring to the water and with the stop watch time how long it takes for the water to completely change colour. Record the time.
  • Once that is complete, pour cold water into a glass. Ask students to predict whether it will change colour faster or slower than the hot water.
  • Add a few drops of food colouring to the water and with the stop watch, time how long it takes for the water to completely change colour. This will take a while so you may want to do something else while you wait.
  • Which liquid took the fastest time to change colour? Discuss why this might have happened.
    (The faster the liquid molecules move, the faster it takes for the food colouring to dilute. The molecules help stir the food colouring around.)
  • Extension: Try using different liquids like milk or juice to see how fast their molecules move.

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