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Changes in Matter - Disappearing Act!

Let's Review!

Changes in physical properties are called physical changes. If the size, shape, or state of a substance changes but the substance itself remains the same, then we say a physical change has occurred.

For example, think about a spoonful of salt. If you add red food coloring to the salt, what would happen? You would still have salt. The change from white to red would be considered a physical change. Despite the red color, it would still taste like salt!

Pretend you took a hammer and used it to crush the salt crystals so that the salt was a powder instead of grainy. Again, the change would be considered a physical change because you would still have salt.

In both examples, only the appearance of the salt changes, not the chemical makeup.

Place a solid substance such as salt in a liquid. Keep track of time until you can no longer see the solid salt. At this point, the salt has dissolved.

Is this an example of a physical change? Write your answer down and then highlight the box below to find out.

Here is a clue: How does salt water taste? Does it taste like salt or like something else? Remember, if it tastes like salt it has not disappeared.  

Because salt water tastes like salt, you know that the salt does not change chemically. Therefore dissolving salt in water is a physical change.

You're the scientist!

Here is a problem for you to solve. You already know that salt water tastes like salt. Can you think of a way to change the salt water back into salt? Write down the steps below and then perform your experiment. Make sure you get an adult to help you.

Stuck?  Think about evaporation

Hypothesis: How do think you can solve the problem?

Procedure: What steps will you take to solve the problem?

Data: Record your observations.

Analysis:

  1. Was your hypothesis correct?
  2. Why do you think it changed back to salt?
  3. How does the amount of salt at the end of the experiment compare to how much salt at the end of the experiment?

Extension: Try a different substance such as Kool - Aid®.

utah state board of education This Sci-ber Text was developed by the Utah State Board of Education and Utah educators.