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Questions and Answers
Which source of water is considered the purest?
What type of impurities can be effectively removed by the method of filtration?
Which method is NOT a physical method of sterilization?
What is the primary characteristic of hard water?
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Which of the following is a method used to remove biological impurities from water?
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Which type of water is typically characterized by the presence of bicarbonates of calcium and magnesium?
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What method is commonly used to remove dissolved salts from water?
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Which of the following contains the highest percentage of salts and organic matter?
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What type of hardness is represented by Mg(HCO3)2 and Ca(HCO3)2?
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Which compound contributes to non-carbonate hardness in water?
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What is the total hardness of water calculated from the given values?
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What is the purpose of EDTA in water hardness determination?
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During the titration process, what color change indicates the end point?
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What is the pH of the buffer solution used in the EDTA titration process?
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Which of the following statements about water hardness is true?
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Which complexing indicator is used in the EDTA method for determining hardness?
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What is the color change observed when EDTA reacts with Mg-EBT?
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How is the total hardness of water calculated?
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Which solution is used to standardize the EDTA?
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What is the volume of hard water sample used in the determination of total hardness?
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What is the molarity of the EDTA solution calculated during the standardization?
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What component is added to the conical flask to change the color of the solution to Wine Red?
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During the determination of permanent hardness, which type of water is used?
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Which formula represents the calculation of the exact molarity of the EDTA solution?
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What is the definition of priming in the context of boilers?
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Which of the following is NOT a common cause of foaming in boilers?
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How can boiler priming be prevented?
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What is the primary reason dissolved salts cause boiler corrosion?
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What is an effective method to remove dissolved oxygen from boiler water?
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Which of the following statements about foaming in boilers is true?
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Which of the following is a disadvantage of wet steam caused by priming?
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What should be added as a preventive measure against foaming?
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What is the definition of scale in the context of a boiler?
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Which salt is known to be less soluble in hot water and is responsible for scale formation?
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Which removal method is used for scale that involves temperature changes?
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What is a disadvantage of scale in boilers concerning fuel costs?
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What is the primary characteristic of sludge in a boiler?
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What causes caustic embrittlement in a boiler?
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In which regions do sludges typically settle in a boiler?
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Which of the following is NOT a method for removing scale?
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Study Notes
Sources of Water
- Rainwater is the purest form of water, containing dissolved gases like CO2, SO2, NO2, Cl2, and H2S.
- Surface water sources include rivers, seas, and lakes.
- River water contains all types of impurities.
- Sea water is the most impure form of water, with a high percentage of salts and organic matter.
- Lake water has a constant composition of impurities with a higher amount of organic matter.
- Underground water is formed when rainwater percolates through the soil, dissolving salts. It is free from organic impurities and is accessed through wells, borewells, and springs.
Impurities in Water
- Suspended impurities are large particles like clay, mud, and organic matter, easily removed through filtration.
- Colloidal impurities are very fine clay and mud particles requiring coagulation for removal. Common coagulating materials include alum and sodium aluminate.
- Biological impurities include microscopic algae, fungi, bacteria, and viruses. These are removed through sterilization by physical methods like boiling and UV light, or chemical methods like chlorine and sodium hypochlorite.
- Dissolved impurities include dissolved gases (CO2, Cl2, H2S, SOx, NOx) and dissolved salts (bicarbonates, sulphates, chlorides, nitrates of Ca, Mg). These are removed through boiling and distillation.
Hardness of Water
- Hard water does not produce lather with soap solutions and contains salts like bicarbonates, chlorides, sulphates, and nitrates of calcium, magnesium, iron, aluminum, and manganese. This is due to the presence of dissolved salts.
- Soft water readily forms lather with soap and is free of salts.
- Temporary hard water is softened by boiling and filtration, as it primarily contains bicarbonates and is removed by heat.
- Permanent hard water contains chlorides and sulphates and requires a separate treatment beyond boiling.
Determining Hardness of Water by EDTA Method
- The EDTA method is a complexometric titration to determine hardness in water.
- Hardness is primarily caused by the presence of bicarbonates, sulphates, chlorides, nitrates of calcium, magnesium, and other heavy metals dissolved in water.
- EDTA (Ethylene Diamine Tetra Acetic Acid) is a complexing agent with a specific structure.
- Eriochrome Black-T (EBT) is the indicator.
- An ammonium hydroxide and ammonium chloride buffer solution is used to maintain a pH of 10.
- EDTA reacts with cations (like Ca2+, Mg2+) to form a stable, colorless complex.
- The endpoint of the titration is marked by a color change from wine red to blue.
Procedure for determining hardness
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Step 1: Standardisation of EDTA
- Fill a burette with 0.01 M ZnSO4 solution.
- Fill another burette with 0.01 M EDTA solution.
- Add 25mL of ZnSO4 to a conical flask.
- Add 5mL of ammonical buffer solution.
- Add 4-5 drops of EBT indicator. The solution will turn wine red.
- Titrate with Na2EDTA from the burette until the solution turns blue.
- Note the reading as V1 mL.
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Step 2: Determination of Total Hardness of Water
- Fill a burette with hard water.
- Fill another burette with 0.01 M Na2EDTA.
- Add 25mL of hard water to a conical flask.
- Add 5mL of ammonical buffer solution and 4-5 drops of EBT indicator. The solution will turn wine red.
- Titrate with Na2EDTA until the solution turns blue.
- Note the reading as X mL.
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Step 3: Determination of Permanent Hardness
- Fill a burette with boiled water.
- Fill another burette with 0.01 M Na2EDTA.
- Add 25mL of boiled water to a conical flask.
- Add 5mL of buffer and EBT indicator.
- Titrate with Na2EDTA until the solution turns blue.
- Note the reading as Y mL.
Calculations
- Molarity of EDTA Solution: Using the formula M1V1 = M2V2, calculate the molarity of the EDTA solution.
- Total Hardness of Water: (X * M2 * 100 * 1000) / Y in ppm.
- Permanent Hardness of Water: (Y * M2 * 100 * 1000) / Z in ppm.
- Total Hardness: Temporary Hardness + Permanent Hardness.
- Temporary Hardness: Total Hardness - Permanent Hardness.
Boiler Issues
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Priming: Violent boiling leading to wet steam due to factors like excessive salts, high steam velocity, sudden temperature change, and improper boiler design.
- Causes: Excessive salts, high steam velocity, sudden change in temperature, improper boiler design.
- Prevention: Use soft water, avoid rapid changes in steam rate, slowly increase temperature, maintain a low water level, install mechanical steam purifiers.
- Disadvantages: Wet steam carries dissolved salts, leading to deposits on turbine blades and heaters, reducing efficiency. Dissolved salts can contaminate other machinery, shortening its lifespan.
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Foaming: Persistent foam on the boiler's surface caused by oil, soaps, or alkaline salts.
- Prevention: Add antifoaming agents like castor oil. Remove oil impurities by adding sodium aluminate.
- Disadvantages: It is difficult to judge the actual height of the water column, making boiler maintenance challenging.
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Boiler Corrosion: Destruction of boiler metal due to chemical or electrochemical attacks by its environment.
- Causes: Dissolved magnesium salts and gases like O2 and CO2.
- Prevention: Remove Mg-salts using zeolites or ion-exchange processes. Add alkali to neutralize acid. Remove O2 by adding reducing agents like sodium sulfite, sodium sulfide, or hydrazine. Remove CO2 by adding liquid ammonia or mechanical de-aeration.
Scale and Sludge
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Scale: Hard, adherent deposits formed on the boiler's inner wall due to salts less soluble in hot water but soluble in cold water.
- Causes: Decomposition of bicarbonates, magnesium salt hydrolysis, silica present in water, and calcium sulfate being less soluble in hot water.
- Removal methods: EDTA treatment, scraping, wire brushing, thermal shock method (rapid temperature changes to crack and loosen scales).
- Prevention: Use soft water.
- Disadvantages: Reduced heat transfer, increased fuel consumption, boiler overheating, material weakening, decreased efficiency, potential for explosions.
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Sludge: Soft, non-adherent precipitate found at the bottom of the boiler.
- Causes: Salts less soluble in cold water.
- Location: Cooler parts of the boiler.
- Disadvantages: Poor heat conduction, wasted heat, entrapped sludge within the scale, excessive sludge blockage, and reduced boiler efficiency.
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Caustic Embrittlement: Brittlement of the boiler metal (corrosion) due to highly alkaline water at high pressure.
- Causes: Free soda (Na2CO3) used as a softening reagent in the lime-soda method.
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Description
Explore the various sources of water and the impurities that affect its quality. Learn about the composition of rainwater, surface water, and underground water, as well as the different types of impurities such as suspended, colloidal, and biological. This quiz will help you understand the significance of water purity.
