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Water Hardness

Water Hardness. Water Hardness. Definition Concerns Scaling Cleaning Public Health. Causes. Table 19.1. Principle cations causing hardness in water and the major anions associated with them. From USGS. Sources. Water Hardness Rating. From USGS. Methods of Determination.

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Water Hardness

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  1. Water Hardness

  2. Water Hardness • Definition • Concerns • Scaling • Cleaning • Public Health

  3. Causes Table 19.1. Principle cations causing hardness in water and the major anions associated with them

  4. From USGS Sources

  5. Water Hardness Rating From USGS

  6. Methods of Determination • Complete Cation Analysis • Most accurate • Calculation of the hardness caused by each ion is performed by use of the general formula: Hardness (mg/L) as CaCO3 = M2+ (mg/L) X 50 EW of M2+ where M2+ represents any divalent metallic ion and EW represents equivalent weight

  7. Example of Complete Cation Analysis • Calculate the hardness of a water sample with the following analysis:

  8. Example of Complete Cation Analysis

  9. Methods of Analysis • Titrimetric Method • Burette • A piece of glassware designed to deliver known amounts of liquid into another container

  10. EDTA • Ethylenediaminetetracetic acid • Chelating agent • Substance whose molecules can form several bonds to a single metal ion • Multi-dentate ligands • Many clawed; holding onto the metal ion to form a very stable complex • 4-6 bonds

  11. EBT • Eriochrome Black • Indicator

  12. A Word about Moles • A mole used in chemistry is something like the term ‘dozen’ we use every day. • The atomic weight of any element, expressed in grams, contains 6.02 x 1023 atoms. • There are 6.02 x 1023 atoms of oxygen in 16 g of oxygen • There are 6.02 x 1023 atoms of hydrogen in 1 g of hydrogen • A mole simply means that you have 6.02 x 1023 of whatever you’re talking about • Avogadro’s number

  13. Molarity • Defined as the number of moles of solute divided by the number of liters of solution • Molarity (mol/L; M) = moles of solute liters of solution • The molar concentration of EDTA in this experiment is 0.005 mol/L.

  14. Example of EDTA Calculation • 50.0 mL tap water sample • 13.75 mL EDTA used in the titration • Calculate the moles of EDTA used. • Calculate the molarity of metal ion present in the tap water sample (Remember: EDTA binds to metal ions on a 1:1 molar ratio). • Find the ppm calcium ion concentration in the sample based on your results from question b).

  15. Example of EDTA Calculation • Calculate the moles of EDTA used Molarity of EDTA = 0.005 mol/L Moles of EDTA = (Molarity)(Liters of EDTA used)

  16. Example of EDTA Calculation • Calculate the molarity of metal ion present (Remember EDTA binds to metal ions on a 1:1 ratio) Molarity of metal ion = moles of EDTA liters of water sample

  17. Example of EDTA Calculation • Calculate concentration of CaCO3 in ppm CaCO3 (ppm) = (Molarity of metal ion)(FW of Ca2+)(1000 mg/g) CaCO3 (ppm) =

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