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Lesson · Grade 7 · Science

Signs of a chemical change

  • Grade 7
  • Science
  • 1 min 7 s
  • British Columbia
  • BC7-SC-20

A second liquid is poured into a beaker, and the beaker then shows each sign of a chemical change in turn: the colour changes, bubbles rise, a solid sinks to the bottom, a thermometer climbs while the beaker glows, and a new smell drifts up, with each sign ticked off on a checklist that ends with "hard to reverse". A caution that one sign alone is not proof leads to the recap: a chemical change makes a new substance.

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In one sentence

The question this lesson answers

How can you tell that a chemical change has happened?

Here is a beaker with a clear liquid. We pour a second liquid in and mix them.

Transcript

What the lesson says

How can you tell that a chemical change has happened?

Here is a beaker with a clear liquid. We pour a second liquid in and mix them.

In a chemical change, a new substance is made. Here are the signs to look for.

Sign one. The colour changes.

Sign two. Bubbles appear. A gas is being made.

Sign three. A solid forms in the liquid and sinks to the bottom. It is called a precipitate.

Sign four. Heat or light is given off. The beaker gets warmer, and it may even glow.

Sign five. There is a new smell, like when an egg goes rotten.

And a chemical change is hard to reverse. You cannot easily get the old substances back.

One sign on its own is not proof. Boiling water bubbles, but no new substance is made.

A chemical change makes a new substance. These signs tell you it has happened.

Curriculum

Where this fits

British Columbia, Grade 7

Science, Chemistry: chemical changesBC7-SC-20

Previous: Why Iron Rusts

The outcomes and strands follow the British Columbia curriculum.

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