ENGINEERING CHEMISTRY CHY 101
Water technology Unit I Water Technology Hardness of water Hard and soft water, Units of Hardness (numerical problems). Disadvantages of Hard water Scale and sludge, Caustic embrittlement, Priming and foaming, Boiler corrosion. Estimation of Hardness EDTA(numerical problems), Alkalinity (Priniciple, procedure and estimation) Softening Internal conditioning: Phosphate, Calgon and methods Carbonate conditioning. Lime soda (numerical problems), Zeolite, Ion exchange, mixed bed deionizer. Treatment of municipal water. Desalination Desalination of brackish water - electrodialysis, reverse osmosis. Sources of Water
Characteristics of Water " Physical Impurities: ±» Colour: Fe, Mn and Chromium ±» Turbidity: Clay ±» Taste: Dissolved minerals: Al, Mn (Bitter) Soapy Taste (Na CO ) 2 3 " Chemical Impurities: ±» Acidity: Acid Rain ±» Gases: CO 2 , CO ±» Minerals ±» Micro-Organisms
Hardness of Water Water Hardness- Characteristic that prevents the lathering of soap ( Caused by dissolved salts of Ca and Mg ) 2C 17 H 35 COONa + CaCl 2 (C 17 H 35 COO) 2 Ca + 2NaCl 2C 17 H 35 COONa + MgSO 4 (C 17 H 35 COO) 2 Mg + 2NaSO 4
Types of Hardness Permanent Hardness (or) noncarbonate hardness Temporary Hardness (or) carbonate hardness - Dissolved bicarbonate salts of Ca - presence of chlorides and sulphates of Ca, Mg and other heavy metals) - Can’t be removed by simple boiling and Mg and other heavy metals such as iron - Can be removed easily by boiling Ca(HCO 3 ) 2 CaCO 3 + H 2 O+ CO 2 Mg(HCO 3 ) 2 Mg(OH) 2 + 2CO 2
HOW TO EXPRESS HARDNESS OF WATER ?
Equivalents of Calcium Carbonate Hardness as well as non-hardness constituting ions are generally expressed in terms of equivalent amount of CaCO 3 Why CaCO 3 Most insoluble salt in water treatment Molecular weight = 100; Equivalent Weight = 50 Mass of Hardness Producing Substance Chemical Equivalent of CaCo 3 Chemical Equivalent of hardness-producing substance X The Equivalents of CaCo 3 = Mass of Hardness Producing Substance Chemical Equivalent of hardness-producing substance X = 50
Units of Hardness 1. Parts per million (ppm) Parts of CaCo 3 equivalent hardness per 10 6 parts of water 2. Milligrams per litre (mg/L) No. of milligrams of CaCO 3 equivalent hardness present per litre of water 3. Clarke’s Degree ( Cl) No. of grains (1/7000lb) of CaCO 3 equivalent hardness per gallon (10lb) of Water (or) parts of CaCO 3 equivalent hardness per 70,000 parts of water 1 grain (64.8 milligrams) of calcium carbonate dissolved in 1 US gallon of water (3.785412 L)
4. Degree French ( Fr) Part of CaCO 3 equivalent hardness per 10 5 parts of water 5. Milliequivalent per litre (meq/L) Milli equivalents of hardness per litre 1 meq/L = 1meq of CaCO3 per litre
Degree French (Fr) : It is the peak of CaCO 3 equivalent hardness per 10 5 parts of water 1 o Fr = 1 part of CaCO 3 equivalent hardness per 10 5 parts 1 o ppm = 1 part per 10,00,000 parts of water 1 o cl = 1 part per 70,000 parts of water 100 ppm = 7 o cl = 10 o Fr 100 100 100 1 ppm = 0.07 o cl = 0.1 o Fr 1 o cl = 1.42 o Fr = 14.2 ppm 1 o Fr = 0.7 o cl = 10 ppm Problem: If the hardness of water is 210.5 ppm Calculate its hardness in o cl 1 ppm = 0.07 o cl 210.5 ppm = 0. 07 ﾗ 210.5 = 14.735 o cl
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