Rocket sets an open cup of vinegar on the scale and dumps in baking soda. Fizz! Bubbles race to the top.
He looks at the screen. "The number went down!" he shouts. "Matter vanished! The rule is broken!"
Raven watches the bubbles pop. "Or did something leave?" she asks. "What do you notice above the cup?"
Nova waves a wing through the air over the cup. "There is a gas here," she says. "Can a scale weigh gas that floats away?"
Rocket blinks. "Oh," he says. "The cup was not closed."
Baking soda and vinegar react to make a new gas called carbon dioxide. The bubbles are that gas.
In an open cup, the gas escapes into the room. The scale cannot weigh gas that has left.
So the number drops, but the matter is not gone. It moved into the air.
Scientists test this with a closed container. A sealed bag works, or a bottle with a balloon on top.
Now the gas is trapped. The scale weighs everything, including the gas.
In a closed container, the weight after the reaction is the same as the weight before.
| Container | Can the gas leave? | What the scale shows |
|---|---|---|
| Open cup | Yes | A lower number, because gas left |
| Closed container | No | The same number as before |
The bubbles are carbon dioxide, a new gas made by the reaction.
Gas is matter, so it has weight.
If the gas floats away, the scale cannot count it. If it is trapped, the scale can.
| Statement | True or false? |
|---|---|
| Baking soda and vinegar make carbon dioxide gas. | ? |
| Gas has no weight. | ? |
| In a closed container, the weight stays the same after a reaction. | ? |
| An open cup lets gas escape into the room. | ? |
Rocket's surprise led to a better test. That is how mistakes help us learn. Tomorrow we will find conserved matter all around us.