The reactivity series — order and how it's built (spec 2.14, 2.15)
K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au. Order determined by reactions with water, acid, oxygen.
The standard 4CH1 reactivity series.
K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au
(C) = carbon, (H) = hydrogen — included as reference points for extraction methods, NOT metals themselves.
Mnemonic. "Please Stop Calling Me A Careless Zebra Instead Try Learning How Copper Saves Gold." — Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold.
Each metal is placed by examining its observed reactions with three reagents: water (cold and as steam), dilute acid (HCl or H₂SO₄), and oxygen. A metal that reacts more vigorously than another is placed higher.
Test 1 — Reactions with cold water.
| Metal | Observation | Reaction |
|---|---|---|
| K | Reacts VIOLENTLY; ignites with lilac flame | 2K + 2H₂O → 2KOH + H₂ |
| Na | Vigorous; melts into ball; moves on surface | 2Na + 2H₂O → 2NaOH + H₂ |
| Ca | Steady fizz; cloudy Ca(OH)₂ forms | Ca + 2H₂O → Ca(OH)₂ + H₂ |
| Mg | Very slow with cold water (faster with STEAM) | Mg + H₂O → MgO + H₂ (steam) |
| Al, Zn, Fe, Cu, Ag, Au | No visible reaction with cold water | — |
So the cold-water test only distinguishes the top few — K, Na, Ca.
Test 2 — Reactions with dilute HCl.
| Metal | Observation |
|---|---|
| K, Na, Ca | Reacts EXPLOSIVELY — dangerous; not normally tested |
| Mg | Reacts vigorously — strong fizz; H₂ pops |
| Al | Reacts slowly (oxide layer needs to be removed first); then vigorously |
| Zn | Reacts steadily — fizz |
| Fe | Reacts slowly — gentle fizz; pale green FeCl₂ solution |
| Cu, Ag, Au | NO reaction — below H in the series |
General equation: M + nHCl → MClₙ + (n/2)H₂. Only works for metals ABOVE H.
Test 3 — Reactions with oxygen.
| Metal | Observation |
|---|---|
| K, Na | Burn vigorously with characteristic flames (red, yellow) |
| Mg | Burns brilliant WHITE light → white MgO |
| Al | Slow oxidation forms protective Al₂O₃ |
| Zn, Fe | Slowly form oxide with heat |
| Cu | Slowly forms black CuO on heating |
| Ag, Au | Au does not oxidise; Ag tarnishes very slowly |
Why this order? Reactivity = how readily a metal LOSES its outer electron(s) to form a positive ion. Metals at the top (K, Na) lose electrons most easily (low ionisation energies, weak hold on outer electrons). Metals at the bottom (Au, Ag, Pt) hold their electrons tightly and rarely lose them.
Where carbon and hydrogen fit. Carbon and hydrogen are NOT metals, but they fit into the series at specific positions based on which metals they can REDUCE:
- Carbon is BETWEEN Al and Zn. It can reduce ZnO, FeO, CuO etc. (carbon-reduction extraction), but NOT Al₂O₃ or higher.
- Hydrogen is BETWEEN Fe and Cu. It can reduce CuO, AgO, but NOT FeO (in practice).
These reference points are crucial for choosing extraction methods (next subtopic).
- Series order: K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au.
- Test 1: cold water reactions (only top of series).
- Test 2: dilute HCl reactions (metals above H).
- Test 3: oxygen reactions (intensity of burning).
- C and H are reference points for extraction methods.