Reactivity Series of Metals – In-depth for CBSE Class 10

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1. What is the Reactivity Series of Metals?

• The Reactivity Series is a scientific arrangement of metals in order of their decreasing reactivity.
• It tells us which metals are more likely to react in chemical reactions, like those with water, acids, and other metal salts.
• The series also helps us predict if one metal will displace another from its compound.

Examples:

• Example 1: Sodium is at the top of the series; gold is near the bottom.
• Example 2: Zinc can displace copper from copper sulfate, but copper cannot displace zinc from zinc sulfate.

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2. The Standard Reactivity Order

Here’s a simplified reactivity series, from most reactive to least reactive:

Potassium (K) > Sodium (Na) > Calcium (Ca) > Magnesium (Mg) > Aluminium (Al) > Zinc (Zn) > Iron (Fe) > Lead (Pb) > [Hydrogen (H)] > Copper (Cu) > Mercury (Hg) > Silver (Ag) > Gold (Au) > Platinum (Pt)

• Mnemonic to remember:
  Please Stop Calling Me A Zebra, I Like Her Calling Smart Guys Please!

Examples:

• Example 1: Potassium reacts very rapidly with water, but gold does not react at all.
• Example 2: Iron is more reactive than copper, so it can replace copper from solutions.
• Example 3: Silver and gold, found at the very bottom, are known as noble metals because they do not react easily.

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3. Why do Metals Have Different Reactivities?

• Electron loss: Metals react by losing electrons. Those that lose electrons easily, like sodium or potassium, are more reactive.
• Atomic size: Down the group, atomic size increases and it becomes easier to lose the outer electrons.
• Energy required (ionization energy): Less energy is needed by highly reactive metals to lose electrons.

Examples:

• Example 1: Sodium loses an electron easily to form Na⁺.
• Example 2: Magnesium is less willing to lose its electrons than sodium, so it's less reactive.
• Example 3: Gold holds on to its electrons tightly and rarely forms ions, making it unreactive.

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4. Uses of the Reactivity Series

a) Displacement Reactions

• A more reactive metal will replace (displace) a less reactive metal from its salt solution.

Examples:

• Example 1: When iron nail is dipped in copper sulfate solution, iron displaces copper:

  • Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

• Example 2: Zinc granules displace copper from copper sulfate solution:

  • Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

• Example 3: Copper cannot displace magnesium from magnesium sulfate, so there is no reaction.

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b) Extraction of Metals from Ores

• Highly reactive metals (like K, Na, Ca) are extracted using electrolysis because they cannot be reduced by carbon.
• Moderately reactive metals (like Zn, Fe, Pb) are obtained by reduction with carbon.
• Less reactive metals (like Au, Ag) are often found in the native state and need simple physical separation.

Examples:

• Example 1: Sodium is obtained by electrolysis of molten sodium chloride.
• Example 2: Iron is extracted from iron oxide using coke (carbon) in a blast furnace.
• Example 3: Gold is found as nuggets and just needs to be separated from its rock.

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c) Prevention of Corrosion (e.g., Galvanization)

• Galvanization: Iron objects are coated with zinc. Zinc, being more reactive, protects iron by corroding first.
• Used widely to protect steel bridges, fences, and vehicles.

Examples:

• Example 1: Iron nails are coated with zinc to prevent rusting.
• Example 2: Railway tracks are galvanized for longevity.
• Example 3: Cars often have zinc-coated steel sheets.

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d) Prediction of Reactions with Water and Acids

• Very reactive metals (K, Na, Ca): React vigorously with cold water.
• Metals in the middle (Mg, Zn, Fe): Only some react with steam or acids.
• Unreactive metals (Cu, Ag, Au): Do NOT react with water, steam, or dilute acids.

Examples:

• Example 1: Sodium placed in water reacts explosively.
• Example 2: Iron only reacts with steam—not cold or hot water.
• Example 3: Copper does not dissolve in dilute hydrochloric acid.

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5. Activities and Observations

Activity: Displacement Reaction

Aim: To investigate the displacement of copper by iron.

Materials Needed:

• Copper sulfate solution (blue color)
• Iron nail
• Test tube

Procedure:

1. Pour the copper sulfate solution into the test tube.
2. Add an iron nail into the solution.
3. Leave undisturbed for 20-30 minutes.
4. Observe changes in color and appearance.

Observations:

• The blue solution becomes light green as FeSO₄ forms.
• A brownish layer (copper) forms on the iron nail.
• Proves that iron is more reactive than copper.

Step-by-step Instructions (for class):

1. Label the test tube and pour 10 mL copper sulfate solution into it.
2. Carefully drop a clean iron nail into the solution.
3. Wait 20-30 minutes.
4. Record any color change or deposit seen.
5. Remove the nail and observe the brown copper layer.

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Activity: Reaction with Water

Aim: To observe reactions of different metals with water.

Materials Needed:

• Small pieces of sodium, magnesium ribbon, iron nail
• Water in beakers

Procedure:

1. Drop a small piece of sodium in water—stand back! Observe reaction.
2. Similarly, test magnesium and iron pieces with water.

Observations:

• Sodium reacts explosively, floats, and produces hydrogen gas.
• Magnesium reacts slowly with cold water; more vigorously with hot water.
• Iron shows almost no reaction with cold water; slight reaction with steam.

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Scenario Based Questions

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1. Scenario: Your school laboratory has iron, zinc, and copper metals and their salt solutions.

   • Question: How would you experiment to determine their relative reactivity?
   • Answer: You can set up displacement experiments. Place each metal into the solution of the other metals’ salts and observe if a reaction (like color change or deposition) occurs. The metal that displaces others most often is the most reactive.

2. Scenario: You notice a silver ornament doesn't rust or corrode for many years.

   • Question: What does this indicate about silver's position in the reactivity series?
   • Answer: Silver is low in the reactivity series. It is unreactive and does not corrode easily.

3. Scenario: You have to protect a new iron bridge from rusting.

   • Question: What metallurgical process could you suggest using the reactivity series?
   • Answer: Recommend galvanization, coating the iron object with zinc, as zinc is higher in the reactivity series and will corrode instead of the iron.

4. Scenario: A student wants to extract zinc from zinc oxide.

   • Question: Based on the reactivity series, which extraction method would be most suitable?
   • Answer: Use carbon reduction (heating zinc oxide with carbon) because zinc is moderately reactive and can be displaced from its oxide by carbon.

5. Scenario: While performing a reaction, you add magnesium ribbon to dilute hydrochloric acid and see bubbles.

   • Question: Are these bubbles due to hydrogen gas? Justify using the reactivity series.
   • Answer: Yes. Magnesium is above hydrogen in the reactivity series and reacts with acids to release hydrogen gas.

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Summary

• The Reactivity Series of Metals helps predict displacement reactions, methods of extraction, corrosion, and reactions with acids or water.
• Experimentation, like displacement reactions, helps visually demonstrate the order of reactivity.
• Understanding the series is useful in daily life, industry, and environmental management.

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