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Hardness of Water is caused due to the presence of soluble bicarbonates, chlorides and sulphates of magnesium and calcium. The water with the salts of calcium and magnesium ions is called hard water. It does not form foam with soap. You might have noticed that sometimes while washing your hands there is no foam formed, therefore, it is because of the presence of hard water. It is basically formed when water percolates through the deposits of chalk and limestone which are made up of magnesium and calcium carbonates.
Key Terms: Hardness of Water, Temporary Hardness, Permanent Hardness, Calcium Carbonate, Magnesium Carbonate, Rainwater
Hard Water
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High mineral content water is referred to as "hard water".Hard water is created when water seeps through limestone, chalk, or gypsum deposits. These deposits are primarily composed of calcium and magnesium carbonates, bicarbonates, and sulphates.
For instance, Rainwater is supple by nature. It tends to acquire increasing amounts of calcium and magnesium compounds as it percolates through limestone, gypsum, or chalk deposits and goes through the ground, turning the water into hard water.
Hard Water and Soft Water
Read More: What is Groundwater?
Properties of Hard Water
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There are a few properties of hard water which can be studied as follows:
- It is highly rich in minerals.
- Soap is not so effective.
- There is no formation of foam and lather from soaps.
- The water contains minerals such as calcium and magnesium.
- It tends to leave spots on the dishes after they are washed and dried.
Types of Hardness of Water
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The hardness of water is of two types:
- Temporary Hardness
- Permanent Hardness
Also Read:
Temporary Hardness and Its Removal
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The presence of calcium and magnesium bicarbonates, or Ca(HCO3)2 and Mg(HCO3)2, causes the temporary hardness of the water. It is also known as carbonate hardness. It is known as temporary hardness because it can be easily eliminated by simply boiling and filtering the water.
When the water is boiled the hardness is removed in the following way:
- Ca(HCO3)2 → CaCo3 + H2O + CO2
- Mg(HCO3)2 → MgCO3+ H2O + CO2
After this CO2 escapes into the surrounding. The leftover salts do not dissolve and thus form precipitates.
Read More: Difference Between Hard Water & Soft Water
Ways to Remove Temporary Hardness of Water
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There are various ways which can be used to remove the hardness of water:
- By Boiling
Bicarbonates of calcium and magnesium break down when temporary hard water is heated, forming calcium and magnesium carbonate, which is insoluble. Thereafter, these insoluble salts are left and are then removed by filtration.
Ca(HCO3)2 → ΔCaCo3↓ + H2O + CO2
⇒ Mg(HCO3)2 → ΔMgCO3↓ + H2O + CO2
- By Clark's Method
For carrying out this process Quicklime or Clark's Reagent which is Calcium Hydroxide (CaO) is added. By turning bicarbonates into carbonate, it softens the water. When lime and the bicarbonates in temporary hard water combine, insoluble calcium and magnesium carbonate are produced, which are easily filtered out.
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O
Permanent Hardness and Its Removal
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We refer to the presence of soluble calcium and magnesium salts in water as permanent hardness since boiling cannot dissolve these salts in the water. These salts are present in the form of chlorides and sulphides. The permanent hardness is mainly because of the following compounds or salts:
- CaCl2
- MgCl2
- CaSO4
- MgSO4
Electric kettles, showers, and other bathroom fixtures or items used to boil water may develop a hard, white coating. Due to the water's enduring hardness, this white coating has formed.
Read More: Chemical Properties of Water
Ways to Remove Permanent Hardness of Water
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There are various ways which can be used to remove the permanent hardness of water:
- Calgon’s Method
In this procedure, each of the molecules of Calgon, or sodium hexametaphosphate, which is added to the water, ionises to produce two Na+ ions and one complex anion. Through the adsorption of Ca++ and Mg++ ions, the hardness of water is eliminated. These ions merge with the complex anion to form it. In this way, Ca2+ or Mg2+ ions are removed from the water. It now exclusively comprises Na++ ions. As a result, it stops being hard and instead softens.
- Ion Exchange Resin Method
Using resins, this technique eliminates the water's enduring hardness. Cl- and anion exchange resin are used to exchange Ca++/Mg++ ions and SO4-2 ions (RNH2OH). In this procedure, demineralized water is produced.
2RCOOH + Ca++ → (RCOO)2Ca + 2H+
RNH2OH + Cl– → RNH2Cl + OH–
H+ + OH– → H2O
- Gan’s Permutit Method
This technique uses sodium aluminium orthosilicate, often known as permutit or zeolite, to eliminate the water's enduring hardness.
Ca(HCO3)2 → ΔCaCo3↓ + H2O + CO2
Mg(HCO3)2 → MgCO3 + H2O + CO2
Read More: Structure of Zeolites
Harmful Effects of Hard Water
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There are many harmful effects of hard water. Some of them are listed below:
- Hard water can make clothes and materials look drab and feel harsh to the touch, causing their colours to fade more quickly. They may live less time as a result.
- The accumulation of minerals in heaters, coffee makers, dishwashers, and other appliances may necessitate frequent repairs.
- Dishes are left with a chalky, white residue and develop stains.
- Hard water can dry out skin and hair because it has high quantities of magnesium and calcium.
- It causes stains from soap scum and scale buildup on plumbing fittings like faucets, shower heads, and bathtubs.
- Hard water doesn't work well with steel pipes. Due to the accumulation of minerals, they are easily damaged or obstructed, which affects the water flow. Corrosion, low water pressure, and drainage issues might result from this.
Hard Water Stains
Read More: Physical Properties of Water
Things to Remember
- Hard water is water which contains a high presence of minerals. It contains soluble bicarbonates, chlorides and sulphates of calcium and magnesium. Example: Hard water does not form lather or foam with soap.
- The hardness of water can be divided into two types namely Temporary Hardness and Permanent Hardness. Temporary hardness is due to the presence of magnesium and calcium hydrogen carbonates. The permanent hardness of water is caused due to the presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in water.
- Temporary hardness can be removed by the following methods: (i) By boiling (ii) By Clark's Method. In temporary hardness, water is precipitated out and the residues are filtered out.
- The following methods can remove permanent hardness: (i) Calgon’s Method (ii) Ion Exchange Resin Method (iii) Gan's Permutit Method
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Sample Questions
Ques. What are the disadvantages of using hard water? (3 Marks)
Ans. The disadvantages of using hard water are:
- Hard water should not be used for washing since it is difficult to make soap lather in it.
- Dry skin and hair can be caused by hard water.
- It tends to block water pipes because of the carbonates of calcium and magnesium.
Ques. Can drinking hard water cause problems? (3 Marks)
Ans. Hard water consumption poses no significant health hazards. On the other hand, hard water can result in dry skin and hair. Regularly washing your hair with abrasive water might irritate your scalp. It is due to the presence of carbonates of calcium and magnesium in high quantities.
Ques. State Clark's Method in detail. (3 Marks)
Ans. For carrying out this process, we add quicklime or Clark's Reagent which is Calcium Hydroxide (CaO) is added. By turning bicarbonates into carbonate, it softens the water. When lime and the bicarbonates in temporary hard water combine, insoluble calcium and magnesium carbonate are produced, which are easily filtered out.
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O
Ques. Why is hard water undesirable? (3 Marks)
Ans. Water with a high concentration of dissolved calcium and magnesium is referred to as "hard water." Although hard water isn't unhealthy for you, it can be annoying to use because it clogs up plumbing fittings with minerals and produces subpar soap and/or detergent. Water is a strong solvent that quickly absorbs impurities.
Ques. How is the hardness of water treated? (3 Marks)
Ans. During mechanical treatments, hard minerals are physically removed from the water. The most popular mechanical method for softening water is an ion exchange water softener. Using an ion exchange process, the hardness minerals in the water are swapped out for another substance.
Ques. Why is water containing large amounts of dissolved calcium and magnesium salts referred to as “hard water”? (3 Marks)
Ans. A common characteristic of water that contains dissolved magnesium and calcium chemical compounds, as well as other trivalent and divalent metallic elements, is hard water (also known as water hardness). The term "hardness" was formerly applied to water that was challenging to wash due to its tendency to waste soap.
Ques. What is the permanent hardness of water? (3 Marks)
Ans. We refer to the presence of soluble calcium and magnesium salts in water as permanent hardness since boiling cannot dissolve these salts in the water. These salts are present in the form of chlorides and sulphides. This hardness is also known as non-carbonate hardness.
Ques. Elaborate upon the formation of scum when hard water is treated with soap. (3 Marks)
Ans. Many times, calcium and magnesium salts can be found in hard water. The precipitate is created when soap molecules interact with calcium and magnesium salts. This precipitate starts to float on the water as an off-white layer. We refer to this layer as scum. Due to the scum buildup in hard water, soaps lose their cleansing ability.
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