水的硬度测定v3.0.pptxVIP

Analytical Chemistry Determination of the hardness of water by complexometric titration 1 Cao chen chen Chen dan dan Bai hui zhen Cai jing jing Chen juan 4 2 3 5 Theory Lab Supplies Procedure Results Purpose 1 6 Discuss Analytical Chemistry Analytical Chemistry Purpose Master the theory and method for the determination of the hardness of water by complexometric titration. 3 Analytical Chemistry Theory The total of Ca2+ and Mg2+ is titrated with standard EDTA using an Eriochrome Black T (EBT) indicator. During titrating,EDTA firstly complex with Ca2+, and then with Mg2+.If the sample does not contain magnesium, Mg-EDTA is added to the titration flask to provide a sharp end point with EBT, since calcium does not form a sufficiently strong chelate with the indicator to give a sharp end point. 4 Analytical Chemistry The following equations represent the reaction of EDTA with metals during titration. Titration: Ca2+ + H2Y2- → CaY2 + 2H+ Ca2+ + MgY2 → CaY2 + Mg2+ End point: Mg2+ + HIn2- → MgIn- + H+ MgIn- + H2Y2 → MgY2 + HIn2- + H (red) (colorless) (colorless) (blue) Theory 6 Lab Supplies buret(50mL) pipette the flask (500mL) conical flask (250mL) the reagent bottle (500mL) dish surface a small beaker (100mL) Apparatus Analytical Chemistry Ethylenediaminetetraacetic acid disodium salt (EDTA solid), CaCO3 (solid), triethanolamine, 1:1 NH3 · H2O, 1:1 hydrochloric acid, magnesium solution(1gMgSO4 · 7H2O was dissolved in water and diluted to 200mL), 10 % NaOH solution, calcium indicator, Na2S solution, NH3-NH4Cl buffer solution (pH = 10), chrome black T indicator Reagents 7 Lab Supplies Analytical Chemistry Procedure Analytical Chemistry Weigh 1.12g Na2H2Y2H2O in a 500-mL beaker. Add the deionized water to dissolve the Na2H2Y2H2O in the beaker (slightly warm up the solution), and then store the