Acid meets metal: bubbles appear
Some metals react with an acid. When a teacher puts small pieces of aluminium, iron, zinc or magnesium into a dilute strong acid, bubbles of hydrogen gas rise from the metal. Water alone does not do this, so the acid is what makes the metal change. Hydrogen burns easily, so no flame is ever used near this test, and only a teacher does it in a lab. We do not do it at home. We can still see a safe reaction at home. A grown-up puts a spoon of baking soda in an open cup and adds some vinegar: bubbles of a gas called carbon dioxide rise. This is not a metal, but it shows the same idea: bubbles are a sign that a new substance is being made. The metals gold and silver do not bubble with a weak acid like vinegar.
| Test tube | What is added | What we see |
|---|---|---|
| 1 | aluminium + acid | bubbles |
| 2 | aluminium + water | no change |
Bubble watch. With a grown-up, put a spoon of baking soda in an open cup on a tray. Wear goggles. Add a little vinegar and watch. Draw the cup before and during. Never put a lid on the cup, because the gas needs room.