Complexation Titration of Hard Water 0.9534g EDTA (Purity = 101.6%; H_2O adsorpt

Question

Complexation Titration of Hard Water 0.9534g EDTA (Purity = 101.6%; H_2O adsorption = 0.7%) is weighed out, dissolved and diluted to 250mL to use in a titration of a water sample to determine water hardness. What is the molarity of EDTA to 4 significant figures? Three 50mL aliquots of an unknown water sample are prepared for titration with the EDTA in question 7. If the volumes of EDTA required for titration are 24. 1mL, 25.9mL, 23.3mL, what is the average % (W/W) (assume all Ca) (water hardness)ion in the unknown sample? What is the water hardness in ppm for question 8? Determination of Iron in an Ore Approximately l.58g KMnO_4 is dissolved into 500mL deionized H_2O. Three Na_2C_2O_4 samples weighing 0.2112g, 0.2091g, and 0.2015g are titrated with the KMnO_4 with volumes of 31.5mL, 31.0mL, and 30.7mL, respectively. What is the molarity of KMnO_4? (MW Na_2C_2O_4 = 134g middot mol^-1) The KMnO_4 from question 10 is then used to titrate three iron-ore samples masses of 0.2318g, 0.2153g, and 0.2251g, at volumes of 22.4mL, 20.3mL and 21.6mL. What is the average % iron (by mass) in the original ore sample? (MW Fe = 54.845g middot mol^-1)

Explanation / Answer

Solution:

8. Mass of EDTA measured = 0.9534 g

Molecular weight of EDTA = 292 g/mol

Moles of EDTA = 0.9534/292 = 0.003265 moles

Volume of solution = 250 ml = 0.25 liter

Molarity = moles of EDTA/Volume of solution inliter

= 0.003265/0.25

= 0.01306 M

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