You must have heard about the hard water problem of Gautam Budh Nagar (Noida) – a satellite township located in the Uttar Pradesh state of India. The deposition of salts of magnesium and calcium around the showerhead, taps etc. is common in Noida. In a recent survey, it is found that the level of dissolved solids (TDS) in the city is 2000 mg per litre against the permissible level of 500. Calcium and magnesium minerals are found in abundance in the soil of Noida which causes high amounts of minerals in the water there. Like Noida, many cities of the world are facing the same problem of the hardness of the water. In this article, we will discuss the difference between hard water and soft water in detail. But before understanding the difference between them you need to understand what is hard water and soft water? So, let us understand hard and soft water definitions 1st.
What is Hard Water?
Hard water is the water that contains higher concentrations of minerals such as calcium and magnesium. The presence of sulfates, carbonates, bicarbonates of calcium and magnesium makes water hard. Apart from calcium and magnesium, a variety of dissolved polyvalent metallic ions such as iron, aluminium, zinc and strontium also contribute.
According to WHO, water containing calcium carbonate at concentrations 60-120mg/l is moderately hard, 120-180mg/l is hard, and more than 180mg/l is very hard. Water hardness is the measure of the capacity of water to react with soap and form lather. Hard water generally forms insoluble curd with soap instead of lather.
Hard water is harmful to machines, boilers, human health and marine animals as well. It causes corrosion and scaling.
Types of Hard Water
Hard water can be divided into two types –
-
Temporary hard water
-
Permanent hard water
Temporary hard water contains bicarbonates and carbonates of calcium and magnesium. It is also called alkaline hardness. It can be removed by boiling the hard water. Thus, removal of temporary hardness of water is cheap or less expensive. The reaction involved in the removal of temporary hardness of water by boiling can be expressed as follows –
Ca2+ + 2HCO3– Heat → CaCO3(S) + H2O + CO2
Hardness Scale
On heating, the temporary hard water calcium carbonate or magnesium carbonates get precipitated.
The permanent hardness of water is due to chlorides and sulfates of calcium and magnesium. It is also called non-alkaline hardness. This type of hardness can be removed by treating water with soda. Methods used in the removal of permanent hardness of water are expensive.
What is Soft Water?
The water which gives lather with soap water is called soft water. It contains lower concentrations of minerals such as calcium and magnesium. It contains sodium ions. According to WHO, water containing calcium carbonate at concentrations below 60mg/l is soft water.
The typical dietary contribution of calcium and magnesium is over 80% of the total daily intake. Out of this 30% Ca and 35%, Mg will be absorbed. 5-20% of Ca and Mg comes from drinking water.
Difference between Hard Water and Soft Water
We have explained above what hard and soft water is, now you can easily differentiate them. The difference between hard and soft water is given below for your better understanding –
|
S.No. |
Hard Water |
Soft Water |
|
1. |
It has a higher mineral concentration than soft water. |
It has a lower mineral concentration than hard water. |
|
2. |
It contains calcium carbonate at concentrations of more than 60mg/l. |
It contains calcium carbonate at concentrations below 60mg/l. |
|
3. |
It mainly contains calcium and magnesium ions. |
It contains calcium, magnesium and sodium ions as well. |
|
4. |
It gives an insoluble curd with soap rather than a lather. |
It gives lather with soap. |
|
5. |
It cannot be used as drinking water daily. |
It can be used as drinking water daily. |
|
6. |
It has a characteristic taste. |
It has a salty taste. |
|
7. |
It is formed when water flows through limestone and chalk and other rocks. |
Rainwater is generally soft water. Apart from this soft water can be produced by passing hard water over an ion exchange resin. |
|
8. |
It is not suitable for boilers and other machines. |
It can be used in boilers and other machines. |
|
9. |
It causes adverse effects on skin and hair. |
It doesn’t cause any adverse effects on skin and hair. |
|
10. |
It causes deposits of hard calcium or magnesium salts on taps, showerheads etc. |
It doesn’t cause deposits of hard calcium or magnesium salts on taps, showerheads etc. |
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Water as a Universal Solvent
Importance of Water: Water is needed by everyone and it is available all around us. Almost 70% of the earth’s surface is covered with water. Most water is found in oceans and seas and covers almost 96.5% of the total water present on the earth.
Water is present in three different states that are solid, liquid, and gases. It also makes two-thirds of the human body. Thus, it is an important constituent of our life. Water is also known as the universal solvent and it is an important component of different life processes where water is used as the main component. It is also a wonderful lubricating agent.
Sources of Water:
The sources of water can be classified into two main types:
Surface water and groundwater
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Surface water: Surface water is the water that is found on the surface of the earth. It includes streams, rivers, oceans, and lakes. The other sources of surface water include seas.
Groundwater: Groundwater is the water that is found under the ground.
Properties of Water
When the earth is viewed from space it appears blue due to the presence of water on most parts of the earth. We require water for all life processes such as bathing, cooking, washing, etc. Therefore, it is important to know more about water. It is needed for survival and is unevenly distributed on the surface of the earth. It is the major solvent and dissolves almost every solute. The main properties of water are given below:
General Properties of Water:
Water has no taste or colour.
The water molecule is made of two hydrogen atoms and one oxygen atom. The hydrogen atoms are joined together with strong bonds that cause high melting and boiling point of water.
Water is a wonderful solvent and it is used for transporting ions and molecules needed for metabolism.
Water also has a high latent heat of vaporization and it helps in regulating the body temperature.
Chemical Properties of Water:
The chemical properties of water include the following:
Water is very reactive and it reacts with different substances to form different compounds. Some important reactions of water are:
Amphoteric nature: Water acts as a base and an acid and this means that it is amphoteric. During photosynthesis, water is oxidized to oxygen. As water can be reduced and oxidized it is an important component of redox reactions.
Hydrolysis Reaction:
Water has a strong hydrating property due to its dielectric constant. It can dissolve different ionic compounds. Many covalent and ionic compounds can be hydrolyzed in water.
Properties:
Chemical formula-H2O
Molar mass-18.01528(33) g/mol
Odor-None
Density-Solid:
0.9167 g/ml at 0 °C
Liquid:
0.961893 g/mL at 95 °C
0.9970474 g/mL at 25 °C
0.9998396 g/mL at 0 °C
Boiling point 99.98 °C (211.96 °F; 373.13 K)
Melting point—0.00 °C (32.00 °F; 273.15 K)
Solubility
Water is poorly soluble in aliphatic and aromatic hydrocarbons, and ethers.
It has a high solubility in amines, alcohols, ketones, and carboxylates.
Water can be mixed with dimethyl sulfoxide, 1,4-dioxane, acetone, propanol, ethanol, methanol, and acetaldehyde.
It is partially miscible with diethyl ether, bromine, ethyl acetate, and dichloromethane.