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Hard water and soft water are the two categories of water. They both look the same and are differentiated based on their chemical properties, mainly their mineral composition. You can also tell the difference between each based on how they feel on your skin, or how much they lather with soap.
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Read More: Concepts in Chemistry
Key Takeaways: Hard water, Soft water, Temporary hardness, Permanent hardness, Minerals, Groundwater, Rainwater
What is Hard Water?
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Hard water is the water containing minerals such as bicarbonates, sulfates or chlorides of calcium and magnesium. The presence of these minerals results in hard water not producing lather with soap. Instead, it forms a white precipitate called scum. It also leaves deposits on appliances called scale, which is mainly made up of calcium carbonate, magnesium hydroxide, and calcium sulfate. Hard water can be found mainly in groundwater, such as water in wells and underground streams. These water sources absorb minerals from the ground, making them hard.
Hard Water and Soft Water
Types of Water Hardness
The hardness of water can be categorised into two types:
- Temporary Hardness: Temporary hardness is caused by the presence of calcium and magnesium bicarbonates in water. It can be gotten rid of quickly by boiling water.
Ca(HCO3) → CaCO3 + CO2 + H2O
- Permanent Hardness: Permanent hardness is caused by calcium and magnesium chlorides and sulphates in water. This type of hardness is tougher to get rid of than temporary hardness and requires chemical reactions with other compounds to be removed.
2(C18H35O2) + Mg → Mg(C18H35O2)2
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What is Soft Water?
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Soft water is the water that is almost completely free of the harsh minerals found in hard water. Instead, it contains mainly soluble sodium cations. The absence of these minerals makes soft water gentle. Hard water is converted to soft water by water softening methods. Soft water keeps appliances running, forms a good lather with soap, and keeps your skin from drying up. An example of soft water is rainwater because it is pure and has not been contaminated with minerals on Earth.
Difference Between Hard Water & Soft Water
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The main points of differences between hard water and soft water are given below:
| Hard Water | Soft Water |
|---|---|
| Contains more minerals of Ca2+ and Mg2+ than soft water. | Contains mainly sodium cations. |
| Do not produce lather with soap. | Lathers well with soap. |
| Leaves limescale deposits on plumbing. | Do not leave residue behind. |
| Requires a large amount of soap during washing. | Gets the job done in less amount of soap and water. |
| Has a higher boiling point due to the presence of dissolved salts. | Has a lower boiling point due to less dissolved salts. |
| Contains more than 60 mg/l of calcium carbonate. | Contains less than or equal to 60 mg/l of calcium carbonate. |
| Has a characteristic, more preferred taste. | Has a salty taste. |
| Is more beneficial for health, because it contains salts of calcium. | Has no health benefits. |
| There are 2 types of hardness in water. | There are no sub-types of soft water. |
| Corrodes appliances. | More gentle and keeps appliances running. |
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Advantages & Disadvantages of Hard Water
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The advantages of hard water are as follows:
- Calcium ions in hard water are beneficial to human teeth and bones.
- Hard water reduces risk of heart disease.
- It has a good taste.
- It can be used to brew better beer.
The disadvantages of hard water are as follows:
- Since it requires more soap for cleaning, it leads to wastage of soap.
- Hard water leaves behind deposits on appliances and blocks pipes.
- It also leaves behind scum in bathrooms.
- It can cause clothes to become hardened.
- Hard water needs to be softened, which can be expensive.
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Advantages & Disadvantages of Soft Water
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The advantages of soft water are given below:
- It saves soap as it lathers easily.
- Since it has no harsh minerals, it keeps plumbing safe.
- It keeps appliances healthy.
- Soft water gives soft hair and skin.
The disadvantages of soft water are given below:
- It Contains high levels of sodium, which is linked to heart disease.
- Soft water allows metals such as cadmium and lead to dissolve easily, which are toxic.
Read Also: NCERT Solutions Class 11 Chemistry: Chapter-wise Solutions
Things to Remember
- Water can be divided into hard water and soft water based on its mineral composition.
- Hard water contains bicarbonates, sulfates and chlorides of magnesium and calcium.
- Hard water with temporary hardness contains bicarbonates of calcium and magnesium, and hard water with permanent hardness contains sulfates and chlorides of calcium and magnesium.
- Soft water contains less calcium and magnesium ions and more sodium ions than hard water.
- Soft water is better for washing and for use in appliances, while hard water is good for health.
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Sample Questions
Ques. What are the main differences between hard and soft water? (2 marks)
Ans. The main differences between hard water and soap water are as follows:
- Hard water barely lathers with soap and leaves behind a white precipitate called scum, while soft water lathers extremely well with soap.
- Hard water contains high percentages of calcium and magnesium salts, while soft water contains mainly sodium salts.
Ques. What are the two types of hardness in water? (2 marks)
Ans. The two types of water hardness are:
- Temporary Hardness - It occurs due to the presence of calcium and magnesium bicarbonates in water.
- Permanent Hardness - It occurs due to the presence of calcium and magnesium chlorides and sulphates in water.
Ques. What can be done to remove temporary hardness? (1 mark)
Ans. Temporary hardness can be removed easily by boiling water.
Ques. What are the two ways to remove permanent hardness? (2 marks)
Ans. Permanent hardness can be removed by adding sodium carbonate to the water or by passing it through an ion exchange resin.
Ques. What are the health benefits of drinking hard water? (2 marks)
Ans. Following are the health benefits associated with drinking hard water:
- Drinking hard water can reduce the probability of developing heart disease.
- The calcium present in hard water is good for the teeth and bones.
Ques. How is hard water bad for appliances? (2 marks)
Ans. Hard water can leave deposits called scale in appliances like kettles and leads to limescale buildup in plumbing, causing it to clog up.
Ques. Which type of water takes longer to boil? (2 marks)
Ans. Hard water has a higher boiling point because it contains dissolved minerals, which act as barriers to water molecules being converted to vapour.
Ques. Give examples of hard water and soft water. (1 mark)
Ans. Hard water is mainly groundwater like those found in wells and underground streams. Soft water is natural rainwater.
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