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Hydrogen — Question 6

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Question 6

(a) Name the chemicals required to prepare hydrogen gas in the laboratory.

(b) Give a balanced chemical equation for the reaction.

(c) Draw a neat and well-labelled diagram for the laboratory preparation of hydrogen.

(d) How is hydrogen gas collected? Why?

Answer

(a) Granulated zinc and dilute hydrochloric acid are the chemicals required to prepare hydrogen gas in the laboratory.

(b) Zn + 2HCl ⟶ ZnCl2 + H2 (g)

(c) Below diagram shows the laboratory preparation of Hydrogen gas:

Draw a neat and well-labelled diagram for the laboratory preparation of hydrogen. Hydrogen, Concise Chemistry Solutions ICSE Class 8.

(d) Hydrogen gas is collected by downward displacement of water as it is sparingly soluble in water. Though hydrogen gas is lighter than air, it is not collected by downward displacement of air as a mixture of hydrogen and air can lead to an explosion.

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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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