5.750 ml of a soil sample was dissolved in water up to the volume of 50 ml. An aliquot of 10 ml of the same was transferred to an Erlenmeyer flask and added 10 ml of KOH 1 mol L-1 and 2. Drops of Calcein and the solution that had a yellow coloration was titled to a slightly orange color consuming a volume of 3.9 mL of EDT A 0.0125 mol/L. On the basis of these data reply:

Question

5.750 ml of a soil sample was dissolved in water up to the volume of 50 ml. An aliquot of 10 ml of the same was transferred to an Erlenmeyer flask and added 10 ml of KOH 1 mol L-1 and 2. Drops of Calcein and the solution that had a yellow coloration was titled to a slightly orange color consuming a volume of 3.9 mL of EDT A 0.0125 mol/L. On the basis of these data reply:

A) What calcium content in the soil sample in mol/dm^-3

B) The bottom of the Erlenmeyer flask appears a fine precipitate, what would be the composition of this precipitate?

Answer 1

Check over your post. I'm wondering if that was 2 drops Mg ion you added before titration with EDTA.

Answer 2

To answer these questions, we need to analyze the given information and use some calculations.

A) To determine the calcium content in the soil sample in mol/dm^-3:

1. Calculate the volume of the aliquot that was transferred to the Erlenmeyer flask:
Volume of aliquot = 10 ml

2. Calculate the volume of EDTA solution consumed during titration:
Volume of EDTA solution consumed = 3.9 ml

3. Calculate the concentration of EDTA solution:
Concentration of EDTA solution = 0.0125 mol/L

4. Use the stoichiometry of the reaction between calcium ions (Ca2+) and EDTA to determine the moles of calcium ions reacted:
1 mol of EDTA reacts with 1 mol of calcium ions

Moles of calcium ions reacted = (Volume of EDTA solution consumed) * (Concentration of EDTA solution)

5. Calculate the volume of the soil sample solution that corresponds to the moles of calcium ions reacted:
Volume of soil sample solution = (Moles of calcium ions reacted) * (Volume of aliquot) / (Molarity of KOH solution)

6. Calculate the concentration of calcium ions in the soil sample:
Concentration of calcium ions = (Moles of calcium ions reacted) / (Volume of soil sample solution)

Plug in the given values and calculate to find the concentration of calcium ions in the soil sample (A).

B) To determine the composition of the precipitate at the bottom of the Erlenmeyer flask:
The yellow coloration and slight orange color change indicate the formation of a calcium complex with Calcein during the titration. The precipitate is likely calcium Calcein complex.

So, the composition of the precipitate is calcium Calcein complex (B).

Please note that the exact calculations require knowing the exact volumes and concentrations of all substances used in the experiment.