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ICSE Class 8 Chemistry Question 15 of 18

Hydrogen — Question 2

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Question 7

Draw labeled diagrams for two experiments to prove that - hydrogen is lighter than air.

Answer

Experiment 1

Procedure : Bubble hydrogen gas by means of a small pipe into a dish containing soap solution.

Observation : Soap bubbles filled with H2 rise upwards.

Conclusion : Hydrogen is lighter than air hence soap bubbles filled with hydrogen rise up.

Soap bubble experiment to prove that hydrogen is lighter than air. Hydrogen, Simplified Chemistry Dalal Solutions ICSE Class 8.

Experiment 2

Procedure : Take two dry test tubes.

Test tube 'A' - Filled with hydrogen.

Test tube 'B' - Filled with air.

Place test tube 'B' over test tube 'A' and test the gas in the upper test tube 'B' with a glowing splinter.

Draw labeled diagrams to prove that hydrogen is lighter than air. Hydrogen, Simplified Chemistry Dalal Solutions ICSE Class 8.

Observation : A 'pop' sound is heard in test tube 'B'. [hydrogen burns with a 'pop' sound].

Conclusion : Hydrogen is lighter than air and has moved upwards displacing the air.

Hydrogen - Study Guide | Bright Tutorials
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Chemistry | Chapter 8: HydrogenWeb Content / Study Guide

Hydrogen — Interactive Study Guide

Quick Concept Map

HYDROGEN: Lightest element, symbol H, atomic mass 1
PREPARATION: Zn + dil. H2SO4 → ZnSO4 + H2↑
TEST: Pop test (burns with a pop sound)
PROPERTIES: Colourless, odourless, lightest gas, reducing agent
WATER OF CRYSTALLISATION: Fixed water molecules in a crystal (e.g., CuSO4.5H2O)

Lab Preparation Summary

ItemDetail
ReactantsZinc granules + Dilute sulphuric acid
Word equationZinc + Dilute sulphuric acid → Zinc sulphate + Hydrogen
ApparatusFlat-bottomed flask, thistle funnel, delivery tube, gas jar, trough
CollectionDownward displacement of water (H2 is insoluble)
Drying agentConcentrated H2SO4
TestPop test — burns with a “pop” sound

Key Reactions of Hydrogen

ReactionWord EquationType
CombustionHydrogen + Oxygen → WaterCombination
Reducing CuOCopper oxide + Hydrogen → Copper + WaterRedox
With chlorineHydrogen + Chlorine → Hydrogen chlorideCombination
Haber processHydrogen + Nitrogen → AmmoniaCombination

Water of Crystallisation — Key Data

Common NameFormulaColourH2O Molecules
Blue vitriolCuSO4.5H2OBlue → White (on heating)5
Green vitriolFeSO4.7H2OGreen7
Washing sodaNa2CO3.10H2OWhite10
GypsumCaSO4.2H2OWhite2
Epsom saltMgSO4.7H2OWhite7

Hydrogen as Clean Fuel

AdvantagesChallenges
Highest calorific value (150,000 kJ/kg)Highly explosive — difficult to store
Only product is water — zero pollutionExpensive to produce
Can be made from water (renewable)No fuelling station infrastructure
Fuel cells generate electricity directlyNeeds very high pressure or low temperature for storage

Self-Check Questions

  1. Name the acid and metal used in the lab preparation of hydrogen.
  2. How is hydrogen gas tested? What is this test called?
  3. Why is hydrogen called a reducing agent?
  4. What happens when blue copper sulphate crystals are heated? Is this reversible?
  5. State two advantages and two challenges of using hydrogen as a fuel.

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