In the analysis for total hardness, formation of Ca-EDTA complex in the presence of an magnesium-calmagite indicator (or Mg-Ind) complex involves the ff. reactions: Ca?"(aq) + EDTA? (aq) = Ca-EDTA (aq) KoaEDTA Mg-Ind (aq) = Mg²"(aq) + Ind2-(aq) 1/Kgind Mg"(aq) + EDTA? (aq) = Mg-EDTA (aq) KupEDTA where KoEDTA. Kuging and KugEDTA are the equilibrium constants for the complex formation. The over-all concentration of the Mg-EDTA complex near the endpoint is equal to K EDTA Kind

In the analysis for total hardness, formation of Ca-EDTA complex in the presence of an magnesium-calmagite indicator (or Mg-Ind) complex involves the ff. reactions: Ca?"(aq) + EDTA? (aq) = Ca-EDTA (aq) KoaEDTA Mg-Ind (aq) = Mg²"(aq) + Ind2-(aq) 1/Kgind Mg"(aq) + EDTA? (aq) = Mg-EDTA (aq) KupEDTA where KoEDTA. Kuging and KugEDTA are the equilibrium constants for the complex formation. The over-all concentration of the Mg-EDTA complex near the endpoint is equal to K EDTA Kind

Principles of Instrumental Analysis

7th Edition

ISBN:9781305577213

Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Publisher:Douglas A. Skoog, F. James Holler, Stanley R. Crouch

Chapter24: Coulometry

Section: Chapter Questions

Problem 24.12QAP

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The equilibrium constant for the conjugate acid-base pair HIn+H2OH3O++In is 8.00 10-5. From the additional information in the following table, (a) calculate the absorbance at 430 nmand 600 nm for the following indicator concentrations: 3.00 10-4M,2.00 10-4M, 1.00 10-4M, 0.500 10-4 M, and 0.250 10-4M. (b) plot absorbance as a function of indicator concentration.
6. Titration of Ca²+ and Mg²+ in a 50.00-mL hard water sample required 23.65 mL of 0.01205 M EDTA. A second 50.00-mL aliquot was made strongly basic with NaOH to precipitate Mg2+ as Mg(OH)2(s). The supernatant liquid was titrated with 14.53 mL of the EDTA solution. Calculate the total hardness of the water sample, expressed as ppm CaCO3.
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(b) Using appropriate chemical reactions for illustration, show how calcium present as the dissolved HCO3- salt in water is easier to remove than other forms of hardness, such as dissolved CaCl2. (c) A water has the following analysis: mg/l mg/l Na+ - 20 Cl- - 40 K+ - 30 HCO3- - 67 Ca2+ - 5 CO32- - 0 Mg2+ - 10 SO42- - 5 Sr2+ -2 NO3- - 10 What is the total hardness, carbonate hardness and noncarbonated hardness in mg/l as CaCO3.
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