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Hydrogen — Question 9

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Question 9

(a) Name a process by which hydrogen gas is manufactured.

(b) Give equations for the reactions.

(c) How is hydrogen separated from carbon dioxide and carbon monoxide?

Answer

(a) Bosch process

(b) Equations for the reactions of Bosch process are:

Production of water gas:

Chot coke+H2Osteam→1000°C(CO+H2)water gas−Heat\underset{\text{hot coke}}{\text{C}} + \underset{\text{steam}}{\text{H}_2 \text{O}} \xrightarrow {1000\degree\text{C}} \underset{\text{water gas}}{(\text{CO} + \text{H}_2)} - \text{Heat}

Reduction of steam by water gas:

(CO+H2)water gas+H2Osteam→450°CFe2O3/Cr2O3CO2+2H2+Heat\underset{\text{water gas}}{(\text{CO}+\text{H}_2)} + \underset{\text{steam}}{\text{H}_2 \text{O}} \xrightarrow [\text{450\degree C}] {\text{Fe}_2\text{O}_3/ \text{Cr}_2\text{O}_3} \text{CO}_2 + 2\text{H}_2 + \text{Heat}

(c) Hydrogen is separated from carbon dioxide by passing the mixture through water under pressure, where carbon dioxide gets dissolved leaving behind hydrogen. Carbon dioxide can also be separated by passing it through caustic potash (KOH) solution.

2KOH + CO2 ⟶ K2CO3 + H2O

Carbon monoxide is separated by passing through ammoniacal cuprous chloride in which carbon monoxide dissolves leaving behind hydrogen.

CuCl + CO + 2H2O ⟶ CuCl.CO.2H2O

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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