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A solution of EDTA is prepared by dissolving 1.986 grams of solid in approximately 500 mL of water. A standard calcium ion solution is then prepared by dissolving 0.2191 grams of chelometric calcium carbonate in HCl until dissolved, evaporating off the solvent, then redissolving into a 250.0 mL volumetric flask. A 25.00 mL aliquot of this calcium solution required exactly 26.18 mL of the EDTA solution to reach an Eriochrome Balck T endpoint. What is the concentration of the EDTA solution

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Answer:

0.02088M of EDTA

Explanation:

The Ca²⁺ is chelated in presence of EDTA in a relation 1:1, when there is no free Ca²⁺ the eriochorme black T change its colour showing endpoint.

Thus, we need to find final concentration of Ca²⁺ solution and, thus, we can find concentration of the EDTA solution:

Molarity Ca²⁺ solution:

0.2191g * (1mol / 40.08g) = 0.005467 moles of Ca²⁺ in 250mL = 0.250L:

0.005467 moles of Ca²⁺ / 0.250L = 0.02187M

Moles of Ca²⁺ added:

0.025L * (0.02187 mol / L) = 5.467x10⁻⁴ moles of Ca²⁺ = Moles of EDTA at endpoint.

Molarity EDTA:

5.467x10⁻⁴ moles EDTA / 0.02618L = 0.02088M of EDTA

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