The Reactivity Series
Inorganic Chemistry
Metals with Water and Acids
Metals with water
- Metals high in reactivity react with cold water; metals lower down only react with steam (if at all)
- The general reaction with cold water is:
metal + water → metal hydroxide + hydrogen
- The general reaction with steam is:
metal + steam → metal oxide + hydrogen
| Metal | Behaviour with water |
|---|---|
| Potassium | Reacts violently with cold water; ignites the hydrogen with a lilac flame |
| Sodium | Reacts vigorously with cold water; melts to a silvery ball and fizzes |
| Lithium | Reacts steadily with cold water; floats, fizzes, dissolves |
| Calcium | Reacts fairly briskly with cold water; produces a cloudy white suspension of Ca(OH)2 |
| Magnesium | Reacts very slowly with cold water; reacts much faster with steam |
| Zinc | Only reacts with steam, slowly |
| Iron | Only reacts with steam, slowly |
| Copper, silver, gold | No visible reaction with water or steam |
- Calcium example:
Ca(s) + 2 H2O(l) → Ca(OH)2(aq) + H2(g)
Metals with dilute acids
- A metal will react with a dilute acid only if it sits above hydrogen in the
- The general reaction is:
metal + acid → salt + hydrogen
- The more reactive the metal, the more vigorously it reacts; the metals above calcium (potassium, sodium and lithium) are too dangerous to react with acid in a school lab
- The salt formed depends on the acid (chloride from HCl, sulfate from H2SO4, nitrate from HNO3)
Common exam question
Giving the test for hydrogen
Question: Give the test for hydrogen, after a metal has reacted with a dilute acid or with water, or after an electrolysis (1 mark).
Asked in 5 of the 23 papers: three times for hydrogen from a metal reacting with an acid or with water, twice for hydrogen made by electrolysis. The mark needs both halves of the test: a lighted splint is held at the mouth of the tube and the gas burns with a squeaky pop.
An answer that only says it burns with a pop, without the lighted splint, is ignored in two schemes because it never says how the gas was lit, and three schemes reject a glowing splint outright: that is the test for oxygen. When the hydrogen comes from a metal and an acid, the equation before it carries its own mark, and state symbols are ignored there even when they are wrong.
| Metal | Reaction with dilute HCl | Reaction with dilute H2SO4 |
|---|---|---|
| Magnesium | Mg + 2 HCl → MgCl2 + H2 | Mg + H2SO4 → MgSO4 + H2 |
| Zinc | Zn + 2 HCl → ZnCl2 + H2 | Zn + H2SO4 → ZnSO4 + H2 |
| Iron | Fe + 2 HCl → FeCl2 + H2 | Fe + H2SO4 → FeSO4 + H2 |
| Copper | No reaction (Cu is below H) | No reaction |