Hey, Welcome to Rajasthan Polytechnic (BTER). This blog post is provide you notes of Polytechnic 1st Semester Chemistry Chapter 2: Water
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Introduction
Water is essential for life and is widely used in various industries. Understanding the chemistry of water, particularly its hardness, and how to treat it, is crucial for multiple applications. This chapter explores the classification of water, types of hardness, problems caused by hard water, and water treatment methods.
2.1 Classification of Soft and Hard Water
Soft Water:
- Definition: Soft water is water that easily forms lather (foam) with soap.
- Why it's soft: Soft water contains fewer dissolved minerals, mainly calcium (Ca²⁺) and magnesium (Mg²⁺) ions.
- Example: Rainwater, distilled water.
Hard Water:
- Definition: Hard water doesn’t form lather easily with soap. Instead, it forms a white scum or precipitate.
- Why it's hard: Hard water contains higher concentrations of dissolved minerals like calcium and magnesium ions.
- Example: Groundwater in areas rich in limestone.
Soap Test for Water Hardness:
- Procedure: A soap solution is added to the water.
- If the water produces lather easily, it is soft.
- If no lather forms and a scum forms, the water is hard.
2.1.1 Hardness of Water and Types of Hardness
Hardness of water is caused by the presence of dissolved salts of calcium and magnesium. These salts react with soap to form an insoluble compound, preventing lathering.
Types of Hardness:
Temporary Hardness:
- Cause: Presence of dissolved bicarbonates of calcium (Ca(HCO₃)₂) and magnesium (Mg(HCO₃)₂).
- Removal: Can be removed by boiling the water. On heating, bicarbonates decompose into carbonates, which can be removed by filtration.
Permanent Hardness:
- Cause: Presence of chlorides (CaCl₂, MgCl₂) and sulfates (CaSO₄, MgSO₄) of calcium and magnesium.
- Removal: Permanent hardness cannot be removed by boiling and requires chemical treatment.
Hardness of Water Video Lecture - Watch Now
2.1.2 Degree of Hardness
- Definition: The degree of hardness refers to the concentration of calcium and magnesium ions in water. It indicates how hard or soft the water is.
2.1.3 Units of Hardness
Hardness is measured in several units. The most common ones are:
ppm (parts per million):
- 1 ppm = 1 part of calcium carbonate (CaCO₃) per million parts of water.
mg/L (milligrams per liter):
- Similar to ppm, it expresses hardness as milligrams of CaCO₃ per liter of water.
Degree Clark (°Cl):
- 1°Cl = 1 grain of CaCO₃ per gallon of water.
Degree French (°Fr):
- 1°Fr = 10 mg of CaCO₃ per liter of water.
2.2 Disadvantages of Hard Water
Using hard water has several negative effects, particularly in households and industries:
Soap Wastage: Hard water consumes more soap, as calcium and magnesium ions react with soap to form an insoluble precipitate, reducing its effectiveness.
Lime Scale Formation:
- In Household Appliances: Hard water forms scale in kettles, washing machines, and pipes, reducing efficiency and causing damage.
- In Industrial Boilers: The formation of scale and sludge can lower boiler efficiency, increase fuel consumption, and lead to serious damage.
Laundry Problems: Hard water makes clothes stiff and rough because soap does not dissolve well.
Health Impact: While drinking hard water doesn’t have severe health effects, prolonged consumption of highly mineralized water may affect the kidneys.
Problems in Boilers Due to Hard Water
Scale and Sludge Video Lecture - Watch Now
Scale and Sludge Formation:
- Scale: Hard, insoluble deposits of calcium and magnesium salts that stick to the boiler walls.
- Sludge: Soft, loose deposits that settle at the bottom of the boiler.
- Effect: Both scale and sludge reduce heat transfer efficiency, increase fuel costs, and can cause overheating and damage to the boiler.
Corrosion:
- Cause: Dissolved salts in hard water, especially chlorides and sulfates, can cause rusting of the boiler's metal parts.
- Effect: This weakens the metal and can lead to leaks or even boiler failure.
Priming and Foaming:
- Priming: The process of water being carried along with steam, which should ideally be pure steam. It is caused by dissolved salts.
- Foaming: The formation of stable bubbles or froth on the water surface inside the boiler.
- Effect: Both problems can cause inefficient operation and contamination of machinery.
Boiler Corrosion Video Lecture - Watch Now
Priming and Foaming Video Lecture - Watch Now
2.3 Water Softening Techniques
Water softening removes hardness-causing minerals (calcium and magnesium) from the water.
2.3.1 Lime-Soda Process
- Process: Involves adding lime (Ca(OH)₂) and soda ash (Na₂CO₃) to hard water.
- Reaction:
- Lime removes temporary hardness by precipitating calcium as calcium carbonate (CaCO₃).
- Soda removes permanent hardness by precipitating calcium and magnesium as insoluble carbonates.
- Advantages: Inexpensive and effective for large-scale water treatment.
- Disadvantages: Produces sludge that must be removed and disposed of.
2.3.2 Zeolite Process
- Process: Involves passing hard water through a bed of zeolite, which is a natural or synthetic material that exchanges sodium ions (Na⁺) for calcium and magnesium ions.
- Reaction:
- Ca²⁺ + Na-Zeolite → Na⁺ + Ca-Zeolite
- Mg²⁺ + Na-Zeolite → Na⁺ + Mg-Zeolite
- Regeneration: Once zeolite becomes saturated with calcium and magnesium ions, it can be regenerated by washing it with a strong sodium chloride (NaCl) solution.
- Advantages: Effective and easy to operate.
- Disadvantages: The zeolite bed requires periodic regeneration.
Water Softening Methods Video lecture - Watch Now
2.4 Municipal Water Treatment
Municipal water treatment involves several steps to ensure the supply of clean, safe drinking water.
1. Screening:
- Purpose: The first step in water treatment, where large debris such as leaves, sticks, and other solids are removed using screens.
2. Sedimentation:
- Purpose: To allow suspended particles to settle at the bottom of a tank.
- Process: Water is left undisturbed in large sedimentation tanks, where gravity causes the heavier particles to settle.
3. Sedimentation with Coagulation:
- Purpose: To remove fine particles that don’t settle easily.
- Coagulants Used: Chemicals like alum (Al₂(SO₄)₃) or iron salts are added to water, which causes fine particles to clump together and settle more easily.
4. Filtration:
- Purpose: To remove remaining fine particles and bacteria from the water.
- Process: Water is passed through layers of sand, gravel, and charcoal that trap and remove impurities.
5. Sterilization (Disinfection):
- Purpose: To kill harmful bacteria, viruses, and microorganisms.
- Methods:
- Chlorination: Adding chlorine (Cl₂) to water to kill pathogens.
- Ozonation: Using ozone (O₃) gas to disinfect water.
- Ultraviolet (UV) Treatment: Exposing water to UV light to kill microorganisms.
Municipal Water Treatment Video Lecture - Watch Now
These notes should help you in understanding water chemistry for exams. The detailed explanation of each concept will assist you in answering both short and long questions effectively. These Notes are Made by Garima Kanwar according to Syllabus provided by BTER (Board of Technical Education Rajasthan, Jodhpur) for Polytechnic 1st Semester Students.
Hope this post will help you. Write down Your query and Suggestion in Comment Section.
Thankyou
Regards
Garima Kanwar
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