Consider the possibility that the EDTA used in this experiment was not as dry as
ID: 491266 • Letter: C
Question
Consider the possibility that the EDTA used in this experiment was not as dry as it should have been. a. Would the concentration of EDTA be higher or lower than the actual value? Explain your answer. Answers without explanation will not be given any credit. b. The determined calcium ion concentration in the unknown would be higher or lower value? Explain your answer. Answers without explanation will not be given any credit. A 0.4505 g sample of CaCO_3 was dissolved in HCl and the resulting solution diluted to 250.0 mL in a volumetric flask. A 25.00 mL aliquot of the solution required 29.25 mL of EDTA solution for titration to the Eriochrom Black T end point. What is the molar concentration of the EDTA solution?Explanation / Answer
1.a)
Suppose we want to measure 5 grams of EDTA for an experiment.
If the EDTA is pure then the 5 grams that you measured is all EDTA.
But if it is not pure(i.e not dry) then measured 5 grams will contain less than 5 grams of EDTA and remaining is water.
Since Molarity(concentration) = (Mass of EDTA/Molar mass of EDTA) / Volume of Solution
If we prepare solution from the impure EDTA the concentration of EDTA will be less than as it sholud have been if we prepare it from pure EDTA.
1.b)
The reaction of metal with EDTA anion can be written as
Mn+ + Y4- _______________> MY(n-4)+
EDTA combines with metal in 1:1 ratio regardless of the charge of the cation.
If we prepare a solution of EDTA from impure EDTA the concentration of EDTA will be less than as it should have been.
So of the concentration of Ca2+ is1M then we need 1M EDTA. But we have prepared less than 1M say 0.8M EDTA.
Then our EDTA solution will only detect 0.8M of Ca2+.
So the determined concentration will be less than the actual value
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