Chapter8

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Unformatted text preview: so high that the water could be considered hazardous waste.” http://www.loe.org/ETS/organizations.php3?action=printContentItem&orgid=33&typeID=18&itemID=195#feature3 Chem 6A Michael J. Sailor, UC San Diego 37 Use of monochloramine in water purification April, 1999 Guidance Manual from EPA: “Use an alternative or supplemental disinfectant or oxidant such as chloramines or chlorine dioxide that will produce fewer DBPs (Disinfectant Byproducts).” “Monochloramine, and chlorine dioxide are typically used to maintain a disinfectant residual in the distribution system” Chem 6A Michael J. Sailor, UC San Diego 38 Use of monochloramine in water purification Chlorine: Cl2 + H2O → HOCl Monochloramine: + H+ + Cl- NH3 + HOCl → NH2Cl + H2O • Monochloramine kills bacteria too • Not as strong an oxidant as chlorine or hypochlorite • Produces fewer potentially toxic or carcinogenic byproducts Chem 6A Michael J. Sailor, UC San Diego 39 Presence of lead in simulated drinking water 2 months after switching to chloramine disinfectant water disinfected with chlorine Rebecca Renner, ENVIRONMENTAL SCIENCE & TECHNOLOGY JUNE 15, 2004 Chem 6A Michael J. Sailor, UC San Diego 40 Chemistry of lead oxides oxidation state: + 4 Hypochlorite reaction: Pb + 2HOCl → PbO2 + 2HCl Monochloramine reaction: oxidation state: + 2 Pb + NH2Cl + H2O → PbO + NH3 + HCl Solubility in water: PbO: 0.017 g/L at 20 °C Solubility of PbO2 << PbO Chem 6A Michael J. Sailor, UC San Diego 41 Acid-Base Behavior of Oxides Some metal oxides and most metalloid oxides are amphoteric (react with acid or base): acid: Al2O3 + 6H+ → 2Al3+ + 3H2O base: Al2O3 + 2OH- + 3H2O → 2Al(OH)4- Chem 6A Michael J. Sailor, UC San Diego 42 Acid-Base Behavior of Oxides Metal oxides produce basic solutions in water: MgO + H2O → Mg2+ + 2OH Because metals are ionic Nonmetal oxides produce acidic solutions: CO2 + H2O → HCO3- + H+ Because nonmetals are covalent Chem 6A Michael J. Sailor, UC San Diego 43 Acid-Base Behavior of Oxides Metal oxides produce basic solutions in water: PbO + H2O → Pb2+ + 2OH PbO2 + 2H2O → Pb4+ + 4OH Neither is very soluble in water, but PbO >> PbO2 Chem 6A Michael J. Sailor, UC San Diego 44 Chemistry of lead oxides “Changes in pH, drops in ORP, or both could destabilize these PbO2 films, and thus increase plumbosolvency…observations that have been made by some water systems of erratic lead release from lead service lines, and increases...
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This note was uploaded on 11/16/2011 for the course CHEM 6A taught by Professor Pomeroy during the Spring '08 term at UCSD.

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