The Reactivity of Metals

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1. Key words

2. The reactivity series

Some metals react with almost anything in seconds; others stay shiny for thousands of years. Scientists put metals in order in the reactivity series, with the most reactive at the top. You need to know these nine metals:

How do we know the order? By comparing how quickly and how vigorously each metal reacts with the same substance. A more reactive metal gives off gas faster, gets hotter, or reacts with a substance that a less reactive metal cannot react with at all.

3. Metals with oxygen

General word equation: metal + oxygen → metal oxide

4. Metals with water

With cold water: metal + water → metal hydroxide + hydrogen (the solution becomes alkaline). With steam: metal + steam → metal oxide + hydrogen.

Example word equations: sodium + water → sodium hydroxide + hydrogen; magnesium + steam → magnesium oxide + hydrogen.

5. Metals with dilute acids

General word equation: metal + acid → salt + hydrogen. The hydrogen makes bubbles (fizzing). The faster the fizzing, the more reactive the metal.

Examples: zinc + hydrochloric acid → zinc chloride + hydrogen; iron + sulfuric acid → iron sulfate + hydrogen.

6. Comparing reactivity fairly

To put metals in order yourself, change only the type of metal (independent variable) and observe the rate of bubbling, the volume of gas collected, or the temperature rise (dependent variable). Keep these the same (control variables): the size or mass of the metal pieces, the volume and concentration of the acid, the type of acid, and the starting temperature. Wear eye protection; acids are irritants.

7. Inert substances

Some substances are generally unreactive: they do not react with air, water or most chemicals under normal conditions. We describe them as inert.

• Gold is inert: it does not react with oxygen, water or dilute acids. That is why gold coins and jewellery thousands of years old still shine, why gold is found in the ground as the pure element (not combined with other elements), and why it is used for electrical contacts in phones and computers — it never corrodes.
• Silver is very unreactive too, so it is used for jewellery and coins (it slowly goes dull, but it does not react with oxygen, water or dilute acids).
• The noble gases (helium, neon, argon) are inert. Argon fills some light bulbs so the hot filament does not react; helium fills balloons and airships because, unlike hydrogen, it cannot burn.
• Glass is inert to most chemicals, which is why test tubes and beakers are made of glass.

Why use inert substances? Something that does not react will not corrode, will not contaminate what it touches, and will not catch fire — so it is safe and long-lasting. The more reactive a metal, the more likely it is found combined in rocks (ores), not as the pure metal.

8. Worked examples

Worked example 1 — Put these metals in order of reactivity, most reactive first: iron, sodium, copper, magnesium. [1]

1. Use the series: potassium, sodium, calcium, magnesium, zinc, iron, copper, silver, gold.
2. Answer: sodium, magnesium, iron, copper.

Worked example 2 — Complete the word equation: zinc + sulfuric acid → __________ + __________ [2]

1. Pattern: metal + acid → salt + hydrogen.
2. zinc sulfate (1) + hydrogen (1).
3. Common mistake: writing "water" as the second product — water is made with metal oxides, not metals.

Worked example 3 — Describe two observations you would see when a small piece of sodium is added to water. [2]

1. Any two: it floats; it fizzes (bubbles of gas); it moves quickly around the surface; it melts into a ball; it gets smaller and disappears; it may burn with an orange flame.
2. Exam tip: "observations" means what you see or hear — not "hydrogen is made" (you cannot see that it is hydrogen).

Worked example 4 — A student adds metals to dilute acid and measures the temperature rise. Results: metal A +2 °C, metal B +14 °C, metal C 0 °C, metal D +7 °C. The metals are copper, iron, magnesium and zinc. Identify each metal. [2]

1. Bigger temperature rise = more vigorous reaction = more reactive.
2. Order: B (14) > D (7) > A (2) > C (0).
3. So B = magnesium, D = zinc, A = iron, C = copper (no reaction). (2 marks all correct; 1 mark for two correct.)

Worked example 5 — Explain why magnesium is used in fireworks and flares, but gold is not. [2]

1. Magnesium is reactive — it burns in oxygen with a very bright white flame (1).
2. Gold is inert — it does not react with oxygen, so it would not burn (1).

Worked example 6 — A metal reacts steadily with cold water and the water turns cloudy. When it is added to dilute acid it fizzes very vigorously. Which metal from the list could it be? Give a reason. [2]

1. Calcium (1).
2. It reacts with cold water but not violently, and it sinks and makes cloudy calcium hydroxide; sodium and potassium are far more violent, and magnesium hardly reacts with cold water (1).

Practice

All pages in this course

Start here

• Stage 8 Science: The Tests and How to Prepare
• Thinking and Working Scientifically: Models, Investigations and Analysing Results

Biology

• Joints and Antagonistic Muscles
• Blood and Its Components
• Breathing, Gas Exchange and Diffusion in the Lungs
• A Balanced Diet, Energy Stores and Lifestyle
• Aerobic Respiration
• Ecosystems, Bioaccumulation and Invasive Species

Chemistry

• The Structure of the Atom
• Purity, Concentration and Chromatography
• Word Equations, Exothermic and Endothermic Reactions
• The Reactivity of Metals
• Impure Products and Solubility of Salts

Physics

• Speed and Distance–Time Graphs
• Balanced and Unbalanced Forces, and Moments
• Pressure, Particles and Diffusion
• Reflection and Refraction
• Dispersion and Colour
• Magnetic Fields and Electromagnets

Earth and space

• The Earth's Magnetic Field and Earth's Resources
• Climate, Weather and Climate Change
• Galaxies and Asteroids

Practice tests

• Stage 8 Science — Practice Test 1
• Stage 8 Science — Practice Test 2
• Stage 8 Science — Practice Test 3