Water which does not produce lather with soap is hard water, and this is due to the presence of soluble bicarbonates, chlorides, and sulfates of calcium and magnesium.

Water is essential for life on Earth, and it can be found in oceans, rivers, ponds, lakes, glaciers, and more. Rainwater is generally considered pure, as it doesn’t contain any salt, although there are dissolved gases present.

JEE Main 2021 LIVE: Chemistry Paper Solutions for 24-Feb Shift-1 (Memory-Based)

Water can be classified as hard water and soft water.

Soft Water: It lathers easily with soap. Rainwater is an example of soft water, which is suitable for household purposes such as laundry and cleaning.

Hard water: It is known as hard water due to the presence of calcium and magnesium salts. When soap is used, it does not lather, but instead forms a precipitate.

⇒ Check: Differences Between Hard Water and Soft Water

![Hard water image]()

Table of Contents

What is Hard Water?

Types of Hardness of Water

Disadvantages of Hardness

How to Remove Temporary Hardness of Water?

How to Remove Permanent Hardness of Water?

Harmful Effects of Hard Water

What is Hard Water?

Hard water is water that contains high levels of dissolved minerals, such as calcium and magnesium. It is usually caused by the water coming into contact with limestone or chalk deposits in the ground.

Hard water contains a high concentration of minerals, such as magnesium and calcium carbonates, which are derived from chalk and limestone deposits. As it does not form a lather with soap, it is not suitable for washing clothes.

Hard water can lead to many problems over a long period of time, such as:

• Deposition of salts, which reduces the efficiency of boilers
• Damage to pipes and other plumbing fixtures
• Unpleasant taste and odor in drinking water
• Skin and hair problems due to the presence of minerals in the water

Strains in Skin

Water appliances working harder can lead to increased water bills.

Spots can be found on clothing and linens.

#Types of Hardness of Water

The hardness of water can be classified into two types:

Temporary Hardness

Permanent Hardness

Causes of Temporary Hardness of Water

The presence of magnesium and calcium carbonates in water makes it temporarily hard. In such cases, the hardness in water can be removed by boiling the water.

When we boil water, the soluble salts of Mg(HCO3)2 are converted to Mg(OH)2, which is insoluble and thus precipitates and is removed. After filtration, the resultant water is soft water.

Causes of Permanent Hardness of Water

When the soluble salts of magnesium and calcium are present in the form of chlorides and sulphides in water, we refer to it as “permanent hardness” as this hardness cannot be eliminated by boiling.

We can soften hard water by treating it with washing soda. When washing soda reacts with the sulphide and chloride salts of magnesium and calcium, insoluble carbonates are formed, thus converting hard water to soft water.

Disadvantages of Hardness

• Hardness can make materials more brittle
• Hardness can make materials more difficult to machine
• Hardness can reduce the ductility of materials

1. Reducing Soap Waste

2. Wastage of Fuel

3. Formation of scales on metallic boilers.

⇒ Further Reading: Heavy Water - Methods of Preparation and Properties

Remove Hardness of Water (Temporary)

By Boiling:

Boiling is a method of cooking food by submerging it in boiling liquid, such as water or oil.

Soluble bicarbonates are converted into insoluble carbonates which can then be removed by filtration.

Reactions: CaCO₃ → CaO↓ + CO₂↑

Mg(HCO3)2 → MgCO3↓ + H2O + CO2

By Clark’s Method:

Calcium hydroxide [1] is commonly known as Clark’s reagent. It is used to reduce the hardness of water by converting bicarbonates into carbonates.

Reaction: 2Ca(OH)2 + Ca(HCO3)2 → 3CaCO3↓ + 2H2O

How to Remove Permanent Hardness of Water?

Gan’s Permutit Method

In this method, Sodium Aluminum Orthosilicate (known as Permutit or Zeolite) is used to remove the permanent hardness of water.

Reaction: Na2Al2Si2O8.KH2O + Ca²⁺ → 2Na⁺ CaAl2Si2O8.xH2O

Calgon’s Process

In this method, Sodium-Hexametaphosphate (NaPO₃)₆ (commonly known as Calgon) is used to remove hardness in water by adsorbing Ca⁺⁺ and Mg⁺⁺ ions.

⇒ Check: Difference between Adsorption and Absorption

Ion Exchange Resin Method:

The process of removing permanent hardness from water involves exchanging Ca++/Mg++ ions with Cl– and SO4-2 ions with anion exchange resin (RNH2OH), resulting in demineralized water.

2RCOOH + Ca^{2+} \rightarrow (RCOO)_2Ca^{2+} + 2H^+

RNH2OH + Cl⁻ ⇒ RNH2Cl + OH⁻

H<sup>+</sup> + OH<sup>-</sup> → H<sub>2</sub>O

Harmful Effects of Hard Water

Signs of Hard Water Include:

1. Soap scum buildup
2. White, chalky residue on surfaces
3. Reduced lathering of soap
4. Spots on dishes and glassware
5. Clogged pipes and fixtures

Linens and clothes appear lackluster and feel coarse.

Unsightly stains on white porcelain and limescale accumulation on faucets

Low water pressure from showers due to clogged pipes could be resolved by unclogging the pipes.

Chalky, white residue or spots appear on dishes.

Strains appearing in the shower