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Essential Science for Teachers: Physical Science

Chemical Changes and Conservation of Matter Children’s Ideas About Chemical Reactions

Children’s Ideas About Chemical Reactions

Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science. Consider what evidence might refute this idea, and why a child would be likely to believe this? Once you’ve entered all your answers you can click “printable page” at the bottom of this form to print your answers. You can also click “see possible response” for any question to see one possible response from the series content advisors.

1. Water is a mixture of hydrogen and oxygen.

Several studies have found that children frequently describe compounds as though they are a mixture of elements. While water is a compound, it can only be separated into hydrogen and oxygen by a chemical process called electrolysis. In science, chemical compounds are regarded as single substances containing two or more elements, chemically combined in a fixed proportion by mass.

2. When a chemical reaction results in gas, the product is lighter because gas weighs less.

Many elementary school students may not have had experience with “closed system” chemical reactions — that is, processes where none of the original substances can escape the system. As a result, if their view of a particular change is dominated by the (apparent) disappearance of some material(s), then they are unlikely to understand that mass has been conserved.

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Essential Science for Teachers: Physical Science


Produced by Harvard-Smithsonian Center for Astrophysics. 2004.
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  • ISBN: 1-57680-749-5