Acids, bases and metals
Drop a zinc strip into dilute acid, acid mixed with much water. Bubbles rise fast.
- A zinc strip drops into dilute acid.
- Bubbles of hydrogen gas rise.
- A marble chip drops into acid instead.
- Bubbles of carbon dioxide gas rise.
- The carbon dioxide turns lime water milky.
Lime water is a clear solution of calcium hydroxide. Read each card below. Tap the gas it makes.
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The rule
A dilute acid with a reactive metal gives a salt and hydrogen. An acid with a carbonate gives a salt, water and carbon dioxide.
A salt has a metal joined to part of an acid. ZnSO₄ is one.
A carbonate has a CO₃ group joined to a metal. Marble, CaCO₃, is one.
Baking soda, NaHCO₃, is a hydrogencarbonate. It gives the same products as a carbonate.
Zinc, magnesium and iron are reactive metals. Copper is not. Copper gives no hydrogen with dilute hydrochloric or sulphuric acid.
An acid with a basic metal oxide gives a salt and water. A metal oxide is a metal joined with oxygen. Copper oxide is one.
A base can act on a metal too. Sodium hydroxide with zinc gives hydrogen. This does not work with every metal.
A base with carbon dioxide gives a salt and water.
| Partner | Equation |
|---|---|
| Acid and metal (zinc) | Zn + H₂SO₄ → ZnSO₄ + H₂ |
| Acid and carbonate (marble) | CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ |
| Acid and hydrogencarbonate (baking soda) | NaHCO₃ + HCl → NaCl + H₂O + CO₂ |
| Acid and metal oxide (copper oxide) | CuO + 2HCl → CuCl₂ + H₂O |
| Base and metal (zinc) | 2NaOH + Zn → Na₂ZnO₂ + H₂ |
| Base and carbon dioxide (lime water) | Ca(OH)₂ + CO₂ → CaCO₃ + H₂O |
Two tests name the gas. Hydrogen burns with a pop near a flame. Lime water turns milky with carbon dioxide. That gas also puts out a candle.
Check the marble equation by counting. Each side has 1 calcium, 1 carbon and 3 oxygen atoms. Each side has 2 hydrogen and 2 chlorine atoms too.