🌟 Detailed Notes on Hydrogen

Hydrogen – the first element in the periodic table and the most abundant in the universe – is called the “Fuel of the Future”. From being used in weather balloons and metal extraction to producing clean energy, this tiny atom plays a giant role in chemistry and human life.

1. Basic Information

• Symbol: H
• Atomic Number: 1
• Atomic Mass: 1 u
• Electronic Configuration: 1s¹
• Valency: 1
• Position in Periodic Table: Group I, Period 1
• Discovery: Henry Cavendish (1766)
• Name given by: Lavoisier (from Greek words “hydro” = water, “genes” = forming).

2. Occurrence of Hydrogen

• Most abundant element in the universe (≈70%).
• Found in:

(a) Free State

• Rare on earth, found in traces in the atmosphere.
• Present in volcanic gases, the sun, and stars (main component of stars).

(b) Combined State

• Present abundantly as:
  • Water (H₂O) → ~70% of earth’s surface.
  • Minerals, acids, bases, salts.
  • Organic compounds: carbohydrates, proteins, fats, hydrocarbons.

3. Preparation of Hydrogen

(A) Laboratory Preparation

1. From dilute HCl and zinc (standard method):
   • Reaction: Zn + 2HCl → ZnCl₂ + H₂ ↑
   • Apparatus: Granulated zinc + dilute HCl in Woulf’s bottle, gas collected over water.
2. Why granulated zinc is preferred?
   • Provides larger surface area.
   • Contains impurities (Cu, Pb) → prevent passivation (formation of insoluble zinc layer).
   • Produces steady stream of gas.
3. Important precautions:
   • Do not collect first few bubbles (contain air).
   • Collect gas over water (H₂ insoluble in water).
   • Do not use concentrated H₂SO₄ → reacts violently.
   • Do not use nitric acid (HNO₃) → it is an oxidising agent, oxidises H₂ to water.
   • Do not bring flame near → explosive risk.

(B) Other Laboratory Preparations

1. Reaction with dilute sulphuric acid:
   Zn + H₂SO₄ → ZnSO₄ + H₂ ↑
2. From active metals with water:
   • 2Na + 2H₂O → 2NaOH + H₂ ↑ (very vigorous).
   • Ca + 2H₂O → Ca(OH)₂ + H₂ ↑ (moderate).
   • Mg + H₂O (hot) → MgO + H₂ ↑ (slow).
3. From steam on metals:
   • Zn + H₂O (steam) → ZnO + H₂ ↑
   • Fe + H₂O (steam) → FeO + H₂ ↑
4. From reaction with alkalis:
   • 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂ ↑

(C) Commercial Manufacture

1. Electrolysis of water:
   • 2H₂O → 2H₂ + O₂
   • Collected separately at cathode and anode.
2. Bosch Process (from water gas):
   • Water gas = CO + H₂
   • Step 1: CO + H₂O → CO₂ + H₂ (catalyst Fe₂O₃ + Cr₂O₃ at 450°C).
   • Step 2: CO₂ removed by dissolving in NaOH → pure H₂.
3. Steam reforming of hydrocarbons (CH₄):
   • CH₄ + H₂O → CO + 3H₂ (Ni catalyst, high T).

4. Properties of Hydrogen

(A) Physical Properties

• Colourless, odourless, tasteless, non-poisonous.
• Lightest gas → 14.5 times lighter than air.
• Neutral (neither acidic nor basic).
• Insoluble in water (can be collected by displacement of water).
• Slightly soluble in some metals (Pd, Ni, Pt absorb H₂).
• Highly combustible.

(B) Chemical Properties

1. Combustion:
   • Burns in air/oxygen → pale blue flame.
   • H₂ + ½O₂ → H₂O + heat (explosive in nature).
2. Reducing Property:
   • Reduces metallic oxides → metals.
   • CuO + H₂ → Cu + H₂O
   • Fe₂O₃ + 3H₂ → 2Fe + 3H₂O
3. Reaction with Non-Metals:
   • With chlorine: H₂ + Cl₂ → 2HCl
   • With nitrogen: N₂ + 3H₂ ⇌ 2NH₃ (Haber process).
   • With sulphur: H₂ + S → H₂S
4. Reaction with Metals:
   • Forms metal hydrides.
   • 2Na + H₂ → 2NaH

5. Tests for H2 gas

• Burns with a pop sound → confirmatory test.
• Does not support combustion but burns itself.

6. Uses of Hydrogen

1. As fuel:
   • Used in rockets (liquid H₂ + liquid O₂).
   • Hydrogen fuel cells.
2. Hydrogenation of oils:
   • Converts vegetable oils into margarine/vanaspati ghee.
3. Manufacture of Chemicals:
   • HCl, NH₃, methanol, fertilizers.
4. Welding (oxy-hydrogen flame):
   • Very high temperature flame (~2800°C).
5. Reducing Agent:
   • Extraction of metals from oxides.
6. In balloons, airships, meteorology.

7. Oxidation and Reduction (Redox Reactions)

1. Oxidation:
   • Addition of oxygen OR removal of hydrogen.
   • Example: H₂ + O₂ → H₂O
2. Reduction:
   • Addition of hydrogen OR removal of oxygen.
   • Example: CuO + H₂ → Cu + H₂O
3. Redox Reaction:
   • Oxidation and reduction occur simultaneously.
   • Example: CuO + H₂ → Cu + H₂O
     • CuO (reduced), H₂ (oxidised).

8. Important Notes

• Why HCl used instead of HNO₃?
  HNO₃ is oxidising agent → oxidises H₂ back to water.
• Why not Na or K?
  Too reactive with water → violent & dangerous.
• Why not Ca or Mg?
  Expensive, slower reaction.
• Why granulated zinc?
  Provides better reaction rate, prevents passivation.

9. Recapitulation

• Hydrogen = lightest and most abundant element in the universe.
• Found in combined state (water, acids, bases, minerals).
• Prepared in lab using granulated zinc + dilute HCl.
• Shows neutral physical properties and is highly inflammable.
• Acts as a reducing agent.
• Widely used in industry, hydrogenation, welding, fuel, and chemical synthesis.

10.Summary

• It is a neutral gas.
• It is not poisonous.
• Pure H2 burns with a blue flame.
• Granulated zinc is preferred in lab prep.
• Sodium & potassium react violently with water.
• H2 gas  can be collected over water because it is insoluble in water.
• Major uses include fuels, fertilizers, hydrogenation, and welding.

Hydrogen, though the simplest element, is central to chemistry, industry, and energy. Its ability to act as a reducing agent, its explosive combustion, and its potential in fuel cells make it the green fuel of the future.

✨ Did you know that while Hydrogen is shaping the future of clean energy, history too has its hidden revolutions? Just like science changes our tomorrow, history explains our past.

👉 To dive into fascinating history, check out this article:
7 Secrets of the Delhi Sultanate You Must Know

“If you’re curious to see hydrogen—and other chemistry concepts—come alive in quick, entertaining videos, check out the Periodic VideoYouTube channel by the Royal Society of Chemistry. Their short, well-explained segments are both fun and educational.” Wikipedia