Fifth Grade · Science · week 4

Mixtures vs new substances

Distinguish a mixture, where substances combine but keep their properties and can be separated, from a chemical reaction that forms a new substance.

When you stir together trail mix, raisins, nuts, and pretzels, you still have raisins, nuts, and pretzels. That is a mixture: the parts keep their own properties and can usually be sorted back out. Salt water is also a mixture; you could evaporate the water and get the salt back.

Sometimes, though, mixing two substances makes something brand new that behaves completely differently and cannot be un-mixed back into the originals. Baking soda and vinegar combine and fizz into carbon dioxide gas and other new substances; you cannot separate that fizzing gas back into plain baking soda and vinegar. That kind of change forms a new substance and is evidence of a chemical reaction.

📋 For the teacher
Teach it (10–15 min):
  • Actually run the baking soda and vinegar test in a cup or bottle; the fizz and the cold or warm feeling make new substance concrete, not abstract.
  • Ask every time, could we sort the ingredients back apart? That single question is the mixture test.
  • List reaction clues together on paper, bubbles, color change, smell, temperature change, as a checklist for future observations.
  • Keep the word chemical from sounding scary; point out this happens safely in baking, digestion, and rusting all the time.
Talk about it:
  • What is the difference between a mixture and a new substance forming?
  • What clues tell you a chemical reaction might have happened?
  • Can you think of a mixture and a chemical reaction you have seen in the kitchen?

Mastery looks like: They can sort a set of examples into mixture or new substance formed, using the separate-back-out test and reaction clues.

Common stumbles: Assuming any mixing counts as a chemical reaction; missing that a color or temperature change is meaningful evidence.

Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
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