Chemical and Physical Changes: Examining Paper for Change
Substances can undergo changes that do not always involve chemical reactions. When ice melts and changes to water, the appearance of the substance changes but its chemical composition remains the same. As ice or water, the substance is still H2O. Melting is an example of a physical change. During a chemical change, such as the formation of rust (iron oxide) from iron, a new substance is formed. The following activity will test your ability to differentiate between chemical and physical changes that might occur in a piece of paper.
Envelope prepared by the teacher (see Teacher's Notes) that contains the following four pieces of paper (all the pieces were originally of equal size):
- Burned paper
- Paper that has a circle cut out of the middle
- Paper folded over three times into a square
- Paper that has been soaked in water and dried
- Remove the four papers from the envelope and examine each one. All four papers were the same size before they experienced the changes you now see.
- Examine each paper closely and consider what you know about physical and chemical changes.
- Which of the pieces of the paper do you think experienced chemical changes? Explain your answer.
- Which of the pieces of paper do you think experienced physical changes? Explain your answer.
- In your own words, write a sentence that differentiates chemical from physical change.
- The burned paper was the only one that experienced a chemical change. In this type of change a new substance was formed.
- The cut, folded, and soaked paper experienced physical changes. The appearance of the paper changed, but no new substance was formed.
- Answers will vary, but students need to indicate that a new substance forms as a result of a chemical change.
If you were asked to prepare an envelope of items for another student so he could identify physical and chemical changes, what items would you select, and how could you modify each one to show these types of changes?