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Some metals burst into flame the moment they touch water, while others sit unchanged in damp air for centuries — gold rings dug from ancient graves still gleam. This enormous range of behaviour can be put into a single ordered list called the reactivity series, which ranks metals from the most reactive at the top to the least reactive at the bottom. Once you know that order you can predict how a metal will behave, decide which metal will "win" a competition for oxygen, and explain how each metal is extracted. This lesson opens Topic C4 (Predicting and identifying reactions and products) of OCR Gateway Science A by building the reactivity series from what you can actually see in the laboratory — the reactions of metals with water and with dilute acid.
By the end of this lesson you should be able to recall the order of the reactivity series, describe the reactions of metals with water and with dilute acid, write word and balanced symbol equations for these reactions, and use observations of vigour and rate to place an unknown metal in the series.
The reactivity series is a list of metals arranged in order of how readily they react — most reactive at the top, least reactive at the bottom. The order you need to know, with the non-metals carbon and hydrogen included as reference points, is:
The two non-metals, carbon and hydrogen, are placed in the list because they are useful dividing lines: a metal's position relative to carbon decides how it is extracted (a later lesson), and its position relative to hydrogen decides whether it reacts with dilute acid.
Exam Tip: A common mnemonic for the order is "Please Stop Calling Me A Careless Zebra, Instead Call Someone Good" — Potassium, Sodium, Calcium, Magnesium, Aluminium, (Carbon), Zinc, Iron, (Hydrogen), Copper, Silver, Gold. Learn it cold: nearly every C4 prediction depends on it.
Whether a metal reacts with water — and how violently — is a direct measure of its reactivity. The pattern is:
metal+water→metal hydroxide+hydrogen
For sodium, the balanced equation is:
2Na+2H2O→2NaOH+H2
metal+steam→metal oxide+hydrogen
For magnesium, Mg+H2O→MgO+H2.
The observations grade smoothly down the series. Potassium reacts so violently with cold water that the hydrogen produced ignites with a lilac flame and the metal skims across the surface; sodium fizzes rapidly and melts into a ball that darts about; lithium fizzes steadily but more gently; calcium sinks and produces a steady stream of bubbles. The further down the series, the calmer the reaction.
| Metal | Reaction with cold water | What you see |
|---|---|---|
| Potassium | Violent | Bursts into a lilac flame, moves rapidly, may spark |
| Sodium | Vigorous | Fizzes fast, melts into a ball, darts across the surface |
| Lithium | Steady | Fizzes gently, floats and moves slowly |
| Calcium | Moderate | Sinks, steady stream of bubbles, cloudy mixture |
| Magnesium | Very slow in cold water (reacts with steam) | Few bubbles in cold water |
| Copper, silver, gold | No reaction | Nothing happens |
Exam Tip: For metal + cold water the products are metal hydroxide + hydrogen; for metal + steam they are metal oxide + hydrogen. Mixing these up (e.g. writing an oxide for the cold-water reaction) is a common, avoidable error.
Most metals above hydrogen in the series react with dilute acid (such as hydrochloric or sulfuric acid) to give a salt and hydrogen gas:
metal+acid→salt+hydrogen
For magnesium and hydrochloric acid:
Mg+2HCl→MgCl2+H2
The rate of fizzing is a direct guide to reactivity: the more reactive the metal, the faster the bubbles of hydrogen are given off and the more quickly the metal disappears. The hydrogen produced can be confirmed by the squeaky pop test (a lighted splint gives a squeaky pop) — a test covered in detail later in C4.
| Metal | Reaction with dilute acid | Rate of fizzing |
|---|---|---|
| Magnesium | Vigorous | Very fast — rapid stream of bubbles |
| Zinc | Moderate | Steady fizzing |
| Iron | Slow | Slow bubbles, especially when cold |
| Copper, silver, gold | No reaction | None |
The very reactive metals (potassium, sodium) react with dilute acid dangerously fast — even more violently than with water — so these reactions are not usually carried out in school laboratories. Crucially, metals below hydrogen in the series — copper, silver and gold — do not react with dilute acid at all, because they are less reactive than the hydrogen the acid would have to release.
Exam Tip: Metal + acid always gives salt + hydrogen (never water, and never carbon dioxide — that comes from carbonates). A metal below hydrogen (copper, silver, gold) will not react with dilute acid; remembering this is worth a mark on its own.
A third clue to a metal's reactivity is how readily it reacts with oxygen to form an oxide (metal + oxygen → metal oxide). The pattern follows the series exactly: very reactive metals such as sodium and potassium tarnish almost instantly in air and must be stored under oil; magnesium burns in oxygen with a brilliant white flame to give magnesium oxide, 2Mg+O2→2MgO; iron reacts slowly, rusting over days and weeks; while gold does not react with oxygen at all, which is why it never tarnishes. The speed and vigour of reaction with oxygen is therefore one more way of placing a metal in the series — the faster and brighter the reaction, the more reactive the metal.
Exam Tip: Reaction with oxygen mirrors the same order as water and acid: reactive metals (Na, Mg) oxidise quickly and vigorously, unreactive metals (gold) not at all. All three behaviours — with oxygen, water and acid — give the same reactivity order.
The two non-metals in the list are there because they act as dividing lines that you will use repeatedly. Carbon marks the boundary for extraction: a metal below carbon can be extracted by heating its oxide with carbon, while a metal above carbon cannot and must be extracted by electrolysis (the focus of a later lesson). Hydrogen marks the boundary for reaction with dilute acid: a metal above hydrogen displaces it from the acid and so reacts, while a metal below hydrogen (copper, silver, gold) does not react at all. Keeping these two reference points in mind turns the reactivity series from a list to memorise into a tool for making predictions.
Exam Tip: Remember what each reference point decides: carbon → how a metal is extracted; hydrogen → whether a metal reacts with acid. These two lines do most of the predicting work in C4.
Four metals W, X, Y and Z are added to separate samples of dilute hydrochloric acid. W fizzes very rapidly; X gives slow bubbles; Y shows no reaction at all; Z fizzes steadily but less than W. Place the metals in order of reactivity, most reactive first.
Step 1 — the rate of fizzing measures reactivity: faster fizzing = more reactive.
Step 2 — rank by what was seen: W (very rapid) is most reactive; Z (steady) is next; X (slow bubbles) is below Z; Y (no reaction) is least reactive (it is probably below hydrogen).
Step 3 — write the order: W, Z, X, Y.
Answer: most reactive to least reactive is W → Z → X → Y.
Write a word equation and a balanced symbol equation for the reaction of lithium with cold water.
Step 1 — lithium is a very reactive metal, so it reacts with cold water to give a metal hydroxide + hydrogen.
Step 2 — word equation: lithium+water→lithium hydroxide+hydrogen.
Step 3 — write formulae: Li, H2O, LiOH, H2, then balance. There are 2 H atoms in H2, so we need 2 LiOH and 2 Li and 2 H2O:
2Li+2H2O→2LiOH+H2
Step 4 — check: Li 2 = 2; H 4 = 4 (4 on the left in two waters; 2 in two hydroxides + 2 in H2 on the right); O 2 = 2. Balanced.
Write the balanced symbol equation for zinc reacting with dilute sulfuric acid.
Step 1 — metal + acid → salt + hydrogen. Sulfuric acid gives a sulfate, so the salt is zinc sulfate, ZnSO4.
Step 2 — write the equation: Zn+H2SO4→ZnSO4+H2.
Step 3 — check: Zn 1 = 1; H 2 = 2; S 1 = 1; O 4 = 4. Already balanced.
Answer: Zn+H2SO4→ZnSO4+H2.
Predict whether (a) iron and (b) copper will react with dilute hydrochloric acid, and explain.
Step 1 — find each metal relative to hydrogen. Iron is above hydrogen; copper is below hydrogen.
Step 2 — apply the rule: a metal above hydrogen reacts with acid (giving salt + hydrogen); a metal below hydrogen does not.
Step 3 — conclude: (a) iron reacts (slowly), giving iron(II) chloride and hydrogen, Fe+2HCl→FeCl2+H2; (b) copper does not react, because it is less reactive than hydrogen.
Answer: iron reacts; copper does not.
Exam Tip: To decide whether a metal reacts with dilute acid, ask one question: is it above hydrogen? If yes, it reacts (salt + hydrogen); if no (copper, silver, gold), it does not.
| Misconception | The correct idea |
|---|---|
| "All metals react with acid" | Metals below hydrogen (copper, silver, gold) do not react with dilute acid |
| "Gold is reactive because it is a precious, valuable metal" | Gold is the least reactive common metal — that lack of reactivity is exactly why it stays shiny and is found native |
| "Metal + water always gives a metal oxide" | With cold water the product is a hydroxide; only with steam is it the oxide |
| "Metal + acid gives salt + water" | Metal + acid gives salt + hydrogen; salt + water comes from acid + base |
| "A faster reaction just means a higher temperature" | A faster reaction with the same acid means the metal is more reactive — rate is the evidence for the order |
Question (6 marks): A student adds equal-sized pieces of three metals — magnesium, copper and iron — first to cold water and then to dilute hydrochloric acid, recording what they see. Use the idea of reactivity to predict and explain the observations, and place the three metals in order of reactivity.
Mid-band response: "Magnesium is the most reactive, then iron, then copper. Magnesium fizzes the most in acid and copper does nothing. So the order is magnesium, iron, copper."
Examiner-style commentary: The order is correct and the key observation (copper does nothing) is used. To climb a band, describe what each metal does in both water and acid, and explain the link between the rate of fizzing and reactivity rather than just stating the order.
Stronger response: "In cold water, magnesium reacts only very slowly and iron and copper do not react. In dilute acid, magnesium fizzes rapidly giving off hydrogen, iron fizzes slowly, and copper shows no reaction because it is below hydrogen. The faster the fizzing, the more reactive the metal, so the order is magnesium (most reactive), then iron, then copper (least reactive)."
Examiner-style commentary: A strong, well-evidenced answer that uses observations from both tests and links rate to reactivity. To reach the top band, name the products (salt + hydrogen) and explain why copper does not react in terms of its position below hydrogen.
Top-band response: "With cold water, magnesium reacts only very slowly (a few bubbles), while iron and copper show no visible reaction — none is reactive enough to react quickly with cold water. With dilute hydrochloric acid, magnesium fizzes rapidly, giving off hydrogen and forming magnesium chloride (Mg+2HCl→MgCl2+H2); iron fizzes slowly, forming iron(II) chloride and hydrogen; and copper shows no reaction at all because it lies below hydrogen in the reactivity series and so cannot displace hydrogen from the acid. Because the rate of fizzing is a direct measure of reactivity, the order from most to least reactive is magnesium → iron → copper. This matches their positions in the reactivity series."
Examiner-style commentary: Full marks. It describes both tests, names products with an equation, explains the absence of reaction for copper by its position below hydrogen, and justifies the order using the rate of reaction — a complete, evidence-based deduction.
This content is aligned with OCR Gateway Science A GCSE Chemistry (J248), Topic C4 Predicting and identifying reactions and products. Refer to the official OCR specification document for the exact wording.