1) Use the molarity of the EDTA solution and the average volume of EDTA added to

Question

1) Use the molarity of the EDTA solution and the average volume of EDTA added to calculate the average number of moles of EDTA required for the titration.

Molarity EDTA= .01 & Volume EDTA= .01755 L

Find moles?

2) EDTA reacts with the hard water ions in a 1:1 ratio. Calculate the total number of moles of the metal ions present in the 50 mL of water tested?

3) An experiment to find water hardness required 18.2 mL of 0.0050 M EDTA solution to titrate 40.0 mL of tap water using an Eriochrome Black T indicator. Find the parts per million of calcium.

Explanation / Answer

1)

Molarity = no. of moles / volume

=> 0.01 M = No. of moles / 0.01755 L

=>No. of moles = 0.01 x 0.01755 = 1.755 X 10^-4

2)

For 1:1 EDTA reacting with hard water, No. of moles of EDTA present = No. of metal ions reacting / binding = 1.755 X 10^-4 moles in 0.01755 L

=> In 50 ml or 0.05 L , No of moles of metal ions reacting = (1.755 X 10^-4 /0.01755 )x0.05

= 0.01 X 0.05 = 5 X 10^-4 moles

3) Conc. of tape water (N2) is calculated by law of equivalence

N1V1= N2V2

=> 0.005 x 18.2 = N2 X 40

=> N2= 0.005 X 18.2 /40 = 0.0002275 M

In ppm, no of moles = mass / molar mass

=> mass = 0.0002275 X 40 = 0.0091 gm

As one ppm is equivalent to 1 milligram of something per liter of water (mg/l)

=> conc. in ppm is given as 0.0091 ppm.

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