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 make up.

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.