In this article we cover the chemistry of water hardness, methods used to remove hardness, and the composition of some important everyday and industrial substances. This includes:
- Hardness of water
- Temporary and permanent hardness
- Methods of removing hardness
- Cement
- Glass
- Soaps and detergents
- Micelle formation
- Gunpowder
- Safety matches
- Paper
- Ignition temperature
- Properties of hydrogen and oxygen
Table of Contents
Hardness Of Water
Hardness of water is the characteristic by which water prevents the formation of lather with soap.
Water becomes hard due to the presence of salts of:
- Ca²⁺
- Mg²⁺
- Fe²⁺
The main salts responsible for hardness are:
- Chlorides
- Bicarbonates
- Sulphates
Soap And Hard Water
Soaps are sodium or potassium salts of stearic acid or palmitic acid.
When soap is added to hard water, calcium or magnesium ions react with soap and form a white precipitate.
This precipitate is usually calcium or magnesium stearate or palmitate.
Reaction:
2C₁₇H₃₅COONa + CaCl₂ → (C₁₇H₃₅COO)₂Ca + 2NaCl
Because soap is used up in forming insoluble precipitate, hard water does not form lather easily.
When hardness-causing ions are removed as insoluble soap, water becomes soft and forms lather.
Types Of Hardness
There are two types of hardness:
- Temporary hardness
- Permanent hardness
Temporary Hardness
Temporary hardness is caused by:
- Bicarbonates of Ca²⁺
- Bicarbonates of Mg²⁺
- Carbonates of Fe²⁺
Temporary hardness can be removed by boiling.
During boiling, bicarbonates decompose and form insoluble carbonates.
Reaction:
Ca(HCO₃)₂ → CaCO₃ + H₂O + CO₂
For magnesium bicarbonate:
Mg(HCO₃)₂ → MgCO₃ + H₂O + CO₂
Permanent Hardness
Permanent hardness is caused by:
- Chlorides of calcium, magnesium and iron
- Sulphates of calcium, magnesium and iron
Permanent hardness cannot be removed by boiling.
Example:
CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl
Methods To Remove Hardness Of Water
The chapter gives the following methods:
- Adding slaked lime, also called Clark’s process
- Adding washing soda
- Calgon process
- Ion-exchange process or resin method
- Permutit or zeolite method
- Boiling, for temporary hardness
Washing Soda Process
Washing soda removes hardness by converting soluble calcium and magnesium salts into insoluble carbonates.
Reactions:
CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl
MgSO₄ + Na₂CO₃ → MgCO₃ + Na₂SO₄
The insoluble carbonates settle down and hardness is removed.
Calgon Method
Calgon is sodium hexametaphosphate.
Formula:
Na₆P₆O₁₈
Calgon removes hardness by forming complex compounds with hardness-causing metal ions.
General idea:
- Ca²⁺ and Mg²⁺ ions are trapped in complex form.
- These ions are no longer available to react with soap.
- Water becomes soft.
Clark’s Method
Clark’s method uses slaked lime, Ca(OH)₂.
It removes temporary hardness by converting bicarbonates into carbonates.
Reaction:
Ca(OH)₂ + Ca(HCO₃)₂ → 2CaCO₃↓ + 2H₂O
Here, calcium carbonate precipitates out.
Removal Of Temporary Hardness By Boiling
Temporary hardness can also be removed simply by boiling water.
Reactions:
Ca(HCO₃)₂ → CaCO₃ + H₂O + CO₂
Mg(HCO₃)₂ → MgCO₃ + H₂O + CO₂
The insoluble carbonate separates from water.
Permutit Method Or Zeolite Method
The permutit method uses zeolite.
Zeolite is sodium aluminium orthosilicate.
Formula:
Na₂Al₂Si₂O₈·xH₂O
In this method, Ca²⁺ ions are exchanged with Na⁺ ions.
Reaction:
Na₂Al₂Si₂O₈·xH₂O + Ca²⁺ → 2Na⁺ + CaAl₂Si₂O₈·xH₂O
This removes calcium ions from hard water.
Ion-Exchange Resin Method
In this method, hardness-causing ions such as Ca²⁺ and Mg²⁺ are exchanged by resins.
Reactions:
2RCOOH + Ca²⁺ → (RCOO)₂Ca + 2H⁺
RNH₂OH + Cl⁻ → RNH₂Cl + OH⁻
Then:
H⁺ + OH⁻ → H₂O
This method removes both cations and anions from water.
Cement
Cement is made from:
- Silica, or sand
- Alumina, Al₂O₃
- Lime
- Iron oxide
- Magnesia, MgO
Cement was invented by Joseph Aspdin in England.
It was named Portland cement because it resembled Portland stone, a limestone found on the Isle of Portland.
Portland Cement
Portland cement contains four main components:
- Tricalcium silicate – 3CaO·SiO₂
- Dicalcium silicate – 2CaO·SiO₂
- Tricalcium aluminate – 3CaO·Al₂O₃
- Tetracalcium aluminoferrite – 4CaO·Al₂O₃·Fe₂O₃
Composition Of Cement
| Component | Percentage |
|---|---|
| CaO | 64.64% |
| SiO₂ | 21.28% |
| Al₂O₃ | 5.6% |
| MgO | 2.06% |
| SO₃ | 2.14% |
| Fe₂O₃ | 3.36% |
Glass
Glass is mainly made from silica, SiO₂.
Raw materials required to make clear glass include:
- Silica, SiO₂
- Sodium oxide, Na₂O
- Calcium oxide, CaO
- Magnesium oxide, MgO
- Feldspar, Al₂O₃
Na₂O is obtained from soda ash.
CaO is obtained from limestone or dolomite.
MgO is obtained from dolomite.
Al₂O₃ is obtained from feldspar.
Other raw materials include:
- Sand, SiO₂
- Calcium carbonate, or limestone
- Sodium carbonate, Na₂CO₃
Composition Of Glass
| Material | Percentage |
|---|---|
| Silica, SiO₂ | 73.6% |
| Soda, Na₂O | 16.0% |
| Lime | 5.2% |
| Potash, K₂O | 0.6% |
Pyrex Glass
Pyrex is a type of borosilicate glass.
It is mentioned separately in the chapter as an important type of glass.
Soaps And Detergents
Soaps and detergents are cleansing agents.
They help remove oily dirt because their molecules contain two different parts:
- One part attracts water.
- One part attracts oil or grease.
Soaps
Soaps are water-soluble compounds.
They are prepared by saponification.
In saponification, sodium hydroxide or potassium hydroxide reacts with vegetable or animal oil.
General reaction:
Oil or fat + NaOH → Soap + Glycerol
Glycerol is formed as a by-product.
Soaps are sodium or potassium salts of long-chain fatty acids.
Structure Of Soap Molecule
A soap molecule has:
- Ionic end
- Tail
- Head
The tail is non-polar.
It is hydrophobic or lipophilic.
This means it attracts oil or grease and avoids water.
The head is polar or ionic.
It is hydrophilic.
This means it attracts water.
Detergents
Detergents are amphipathic molecules.
This means they have both:
- Hydrophobic region
- Hydrophilic region
Detergents are also called surfactants.
A detergent molecule contains:
- Charged hydrophilic polar group at one end
- Long lipophilic hydrocarbon group at the other end
In simple words, detergents also have a head and a tail.
Important Terms Related To Detergents
Critical Micelle Concentration
The concentration at which micelle formation starts is called Critical Micelle Concentration, or CMC.
Aggregation Number
The aggregation number is the average number of monomers present in a micelle.
Relative Micelle Size
Relative micelle size indicates the molecular weight of the micelle.
Cloud Point
The temperature at which a detergent solution at or above CMC separates into two phases is called the cloud point.
Micelle Formation
Dirt is oily in nature.
The hydrophilic end of soap is attracted towards water molecules.
The hydrophobic end is directed towards the hydrocarbon part of oil or dirt.
Because of this arrangement, soap molecules surround oily dirt and form a micelle.
This helps lift oily dirt from the surface and allows it to be washed away with water.
Gunpowder
Gunpowder is a homogeneous mixture.
It is a mixture of:
- Sulphur
- Charcoal
- Saltpetre, KNO₃
Saltpetre is potassium nitrate.
Components Of Gunpowder
Charcoal
Charcoal consists mainly of carbon.
It acts as fuel.
Saltpetre
Saltpetre, or potassium nitrate, supplies oxygen for combustion.
Sulphur
Sulphur, also called brimstone, lowers the ignition temperature.
Composition Of Gunpowder
| Component | Percentage |
|---|---|
| Potassium nitrate, KNO₃ | 75% |
| Charcoal, C | 15% |
| Sulphur, S | 10% |
The chapter’s text shows sulphur as 100%, but in the standard black powder composition and the same chapter’s context, it should be read as 10%.
Black Powder Reaction
The reaction given for black powder is:
10KNO₃ + 9C + 3S → 2K₂CO₃ + 3K₂SO₄ + 6CO₂ + 5N₂
Safety Matches
A safety match has two important parts:
- Match head
- Striking surface
Match Head
The match head contains:
- Antimony sulphide
- Potassium chlorate, KClO₃
- Sulphur or charcoal
Potassium chlorate acts as an oxidising agent.
Striking Surface
The striking surface contains red phosphorus.
During friction:
Red phosphorus → White phosphorus
White phosphorus ignites easily and helps start the burning of the match.
Chemicals In Match Head
Important chemicals mentioned in the chapter are:
- P₄S₃ – Phosphorus sesquisulphide
- KClO₃ – Potassium chlorate
Modern Safety Match Box
Modern safety match boxes use:
- Potassium chlorate
- Red phosphorus
Paper
Paper is made from cellulose or wood pulp.
The chapter mentions that paper contains about 90–99% cellulose or wood pulp.
Other materials used in paper making include:
- Cotton
- Flax
- Esparto
- Straw
- Hemp
- Manila
- Jute
Ignition Temperature
Ignition temperature is the minimum temperature required to start or cause combustion.
A substance catches fire only when it reaches its ignition temperature.
Properties Of Different Gases
The chapter discusses important gases, mainly hydrogen and oxygen.
Hydrogen Gas
Chemical formula:
H₂
Physical Properties Of Hydrogen
- Hydrogen is colourless.
- It is odourless.
- It is tasteless.
- It is the lightest element.
- It is highly flammable.
- It burns with a pale blue, almost invisible flame.
- It is insoluble in water.
- Its boiling point is about -252.9°C.
- Its melting point is about -252.2°C.
- It is non-toxic but dangerous in high concentration due to explosion risk.
- It is a poor conductor of heat and electricity.
Chemical Properties Of Hydrogen
Hydrogen exists as a diatomic molecule.
Combustion reaction:
2H₂ + O₂ → 2H₂O + energy
Hydrogen reacts with non-metals and forms compounds such as:
- HCl
- H₂S
- HF
It forms covalent compounds with elements such as:
- Oxygen
- Nitrogen
- Chlorine
Hydrogen can reduce metal oxides.
Example:
CuO + H₂ → Cu + H₂O
Hydrogen also forms hydrides with metals.
Examples:
- NaH
- CaH₂
Different Types Or Colours Of Hydrogen
Green Hydrogen
Green hydrogen is produced by electrolysis of water using renewable energy.
It is considered the cleanest form because it has zero carbon emissions during production.
Black Or Brown Hydrogen
Black or brown hydrogen is produced by gasification of coal or lignite.
It causes high carbon emissions.
Grey Hydrogen
Grey hydrogen is produced by steam methane reforming using natural gas.
It emits CO₂.
Blue Hydrogen
Blue hydrogen is produced from natural gas like grey hydrogen, but carbon capture and storage is used.
Pink Or Purple Hydrogen
Pink or purple hydrogen is produced by electrolysis using nuclear energy.
Turquoise Hydrogen
Turquoise hydrogen is produced by pyrolysis of methane.
It produces solid carbon instead of CO₂.
Oxygen
Chemical formula:
O₂
Properties Of Oxygen
- Oxygen has no colour or smell under normal conditions.
- It is slightly soluble in water.
- Its solubility in water helps aquatic life breathe.
- It supports combustion.
- It exists as a diatomic molecule.
- Liquid oxygen is pale blue.
- It is heavier than air.
- It is essential for respiration in humans and animals.
- It is used by plants during photosynthesis.
Chemical Properties Of Oxygen
Oxygen reacts with carbon:
C + O₂ → CO₂
Oxygen reacts with magnesium:
2Mg + O₂ → 2MgO
Oxygen forms acidic oxides with non-metals.
Oxygen forms basic oxides with metals.
Hydrogen reacts with oxygen:
2H₂ + O₂ → 2H₂O
Oxygen acts as a strong oxidising agent.
Reaction With Oxygen And Flame Colour
| Substance | Reaction With Oxygen | Flame Colour |
|---|---|---|
| Magnesium | Forms MgO | Bright white |
| Sulphur | Forms SO₂ | Blue flame |
| Carbon | Forms CO₂ | Yellow-orange |
| Phosphorus | Forms P₂O₅ | White flame with smoke |
| Hydrogen | Forms H₂O | Pale blue flame |
Oxygen Allotropes
Oxygen has important allotropic forms.
Dioxygen
Dioxygen, O₂, is a colourless gas.
Ozone
Ozone, O₃, is a pale blue gas with a sharp smell.
Ozone is also a strong oxidising agent.
Colours Of Some Oxides
| Element | Oxide Formed | Colour Of Oxide |
|---|---|---|
| Mg | MgO | White |
| Cu | CuO | Black |
| Fe | Fe₂O₃ | Reddish brown |
| Zn | ZnO | White when cold, yellow when hot |
| Pb | PbO | Yellow or red |
FAQs On Composition And Water Treatment
What is hardness of water?
Hardness of water is the property by which water prevents the formation of lather with soap.
Which ions cause hardness of water?
Ca²⁺, Mg²⁺ and Fe²⁺ ions cause hardness of water.
What is temporary hardness?
Temporary hardness is caused by bicarbonates of calcium and magnesium and carbonates of Fe²⁺.
How is temporary hardness removed?
Temporary hardness is removed by boiling or by Clark’s method.
What is permanent hardness?
Permanent hardness is caused by chlorides and sulphates of calcium, magnesium and iron.
Can permanent hardness be removed by boiling?
No, permanent hardness cannot be removed by boiling.
What is Clark’s process?
Clark’s process removes temporary hardness by using slaked lime, Ca(OH)₂.
What is Calgon?
Calgon is sodium hexametaphosphate, Na₆P₆O₁₈, used to remove hardness of water.
What is zeolite?
Zeolite is sodium aluminium orthosilicate used in the permutit method.
Who invented cement?
Cement was invented by Joseph Aspdin in England.
Why is Portland cement called so?
It is called Portland cement because it resembles Portland stone.
What is glass mainly made of?
Glass is mainly made of silica, soda, lime and potash.
What is Pyrex?
Pyrex is borosilicate glass.
What is soap?
Soap is a sodium or potassium salt of long-chain fatty acid.
What is saponification?
Saponification is the reaction of oil or fat with NaOH or KOH to form soap and glycerol.
What is a detergent?
A detergent is an amphipathic surfactant molecule having hydrophilic and hydrophobic regions.
What is CMC?
CMC means Critical Micelle Concentration, the concentration at which micelle formation starts.
What is gunpowder?
Gunpowder is a homogeneous mixture of potassium nitrate, charcoal and sulphur.
What is the role of potassium nitrate in gunpowder?
Potassium nitrate supplies oxygen for combustion.
What is ignition temperature?
Ignition temperature is the minimum temperature required to start combustion.
What does a safety match head contain?
A safety match head contains antimony sulphide, potassium chlorate and sulphur or charcoal.
What is paper made from?
Paper is made from cellulose or wood pulp.
What are the main physical properties of hydrogen?
Hydrogen is colourless, odourless, tasteless, lightest, highly flammable and insoluble in water.
What is green hydrogen?
Green hydrogen is hydrogen made by electrolysis of water using renewable energy.
What are the main properties of oxygen?
Oxygen is colourless, odourless, slightly soluble in water, supports combustion and is essential for respiration.
What are the allotropes of oxygen?
The main allotropes are dioxygen, O₂, and ozone, O₃.
Last Moment Exam Cheat Sheet – Composition And Water Treatment
- Hard water does not form lather easily with soap.
- Ca²⁺, Mg²⁺ and Fe²⁺ ions cause hardness of water.
- Chlorides, bicarbonates and sulphates are responsible for hardness.
- Soaps are sodium or potassium salts of stearic or palmitic acid.
- Hard water reacts with soap to form white precipitate of calcium or magnesium stearate/palmitate.
- Temporary hardness is due to bicarbonates of Ca²⁺ and Mg²⁺ and carbonates of Fe²⁺.
- Temporary hardness can be removed by boiling.
- Permanent hardness is due to chlorides and sulphates of Ca²⁺, Mg²⁺ and Fe²⁺.
- Permanent hardness cannot be removed by boiling.
- Clark’s method uses slaked lime, Ca(OH)₂.
- Calgon is sodium hexametaphosphate, Na₆P₆O₁₈.
- Zeolite is sodium aluminium orthosilicate.
- Ion-exchange resin removes Ca²⁺ and Mg²⁺ ions.
- Cement was invented by Joseph Aspdin.
- Portland cement contains tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite.
- Glass mainly contains silica, soda, lime and potash.
- Pyrex is borosilicate glass.
- Soap is prepared by saponification of oil or fat with NaOH or KOH.
- Soap molecule has hydrophilic head and hydrophobic tail.
- Detergents are amphipathic molecules and surfactants.
- CMC means Critical Micelle Concentration.
- Gunpowder is a homogeneous mixture of potassium nitrate, charcoal and sulphur.
- Potassium nitrate supplies oxygen in gunpowder.
- Sulphur lowers ignition temperature.
- Safety match head contains antimony sulphide, KClO₃ and sulphur or charcoal.
- Striking surface contains red phosphorus.
- Paper is made from cellulose or wood pulp.
- Ignition temperature is the minimum temperature required to start combustion.
- Hydrogen is the lightest element and burns with a pale blue flame.
- Green hydrogen is made by electrolysis using renewable energy.
- Oxygen supports combustion and acts as a strong oxidising agent.
- Dioxygen is O₂ and ozone is O₃.