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ENVE 201 Environmental Engineering Chemistry 1

ENVE 201 Environmental Engineering Chemistry 1 . HARDNESS Dr. Aslıhan Kerç. Hard waters: Require considerable amount of soap Produce scale in hot water pipes , heaters , boilers Synthetic detergents  Minimize hard water problem for household

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ENVE 201 Environmental Engineering Chemistry 1

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  1. ENVE 201EnvironmentalEngineeringChemistry 1 HARDNESS Dr. Aslıhan Kerç

  2. Hard waters: • Require considerable amount of soap • Producescale in hot waterpipes , heaters , boilers Syntheticdetergents  Minimize hard water problem for household Forpersonalhygiene hard water is problem

  3. Differentequipmentareusedtopreventscalling problem Watersofteninprocess Privateandindustrialinstallations Municipalsofteningplants (less) Surface waters are softer than groundwater. Hardness depends on geological formation.

  4. CauseandSource of Hardness Hardness is causedbymultivalentcations. M2+ react w/soap form precipitates M2+ + Anions Scale Ca2+ , Mg2+ , Sr + , Fe2+ , Mn2+ Al3+ , Fe3+alsocontributetohardness , but theirsolubility is negligible @pH of naturalwater. Hardness of water duetocontact w/ soilandrock

  5. Methods of Determination • CalculationMethod • EDTA TitrimetricMethod CalculationMethod Mostaccuratemethod. Completeanalysis of allthecations is required.

  6. Calculationfromconcentration of divalentcations. • AtomicAbs. Spect. (AAS) • InductivelyCoupledPlasma (ICP) • IonChromatography • IonSpecificElectrodes (ISE) Hardness (mg/L as CaCO3) = M2+ (mg/L) * 50 / (E.W M2+)

  7. EDTA TitrimetricMethod • Titratingagent : Ethylnediaminetetraaceticacidoritssodium salt. HOOC-CH2 CH2-COOH N-C-C-N HOOC-CH2 CH2-COOH H H H H

  8. EDTA Molecular Structure

  9. EDTA  chelatingagent, formscomplexeswith Ca2+ , Mg2+ (divalentcations) Mg2+ + EDTA  [ M.EDTA] complex Indicator  show excess EDTA , all ions are complexed EriochromeBlack T (bluecolor)

  10. Mg2+ + Eriochrome Black T  ( M. Eriochrome Black T ) complex Wine Red • As EDTA is added, it makesstablecomplexes w/ Ca2+ and Mg2+ . Types of Hardness Classification in twoways : • Accordingtometallicion • Calciumandmagnesium 2. Accordingtoanionsassociated w/metallicions. • Carbonate , noncarbonate

  11. Types of Hardness Classification in two ways : According to metallic ion Calcium and magnesium 2. According to anions associated w/metallic ions. Carbonate , non carbonate

  12. Calcium – MagnesiumHardness • Ca , Mg causegreatestportion of hardness. • Amount of Mg2+should be knownfor lime soda ashsoftening. • Ca-Mg  Calculatedfromcompleteanalysis • Total hard.– Calcium hard. = Magnesium hard.

  13. Carbonate and Non-Carbonate Hardness • Carbonatehardnessequivalentto (bicarbonate + carbonate) alkalinity. • Whenhardness > CO32- +HCO3-alkalinity Carbonate Hardness = Alkalinity Excess = Non-carbonate hardness

  14. Hardness ≤ Carbonate and HCO-3 alk Carboante hardness = Total Hard • Carbonate Hardness  Temporary hardness ( precipitate at elevated temp., boiling)

  15. Ca2+ + HCO3- CaCO3 + CO2+ H2O Ca2+ +2HCO3- + Ca(OH)2 2CaCO3 + 2H2O • Permanent hardness (Non-carbonate Hardness, NCH) can’t be removed by boiling. • Non-Carbonate Hard.=Total Hard.– Carbonate Hard • Hardnessexpressed as CaCO3 • Non-Carbonatehardnessassociated w/sulfate, chloride, nitrateanions.

  16. Pseudo- Hardness • Whenthere is Na+  interferewith normal behavior of soap. • Na+ is not a hardnesscausingcation. • Highconcentration of Na+  Pseudo-Hardness

  17. Application of Hardness Data • Suitability of waterfordomesticindustrialuse • Softeningprocess

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