A solution contains 1.694 mg CoSO4 (155.0 g/mol) per milliliter. Calculate (a) the volume of 0.08640 M EDTA needed to titrate a 25.00-mL aliquot of this solution. (b) the volume of 0.009450 M Zn2 needed to titrate the excess reagent after addition of 50.00 mL of 0.08640 M EDTA to a 25.00-mL aliquot of this solution.

Moles of any substance is given by the molar mass and the mass. The volume of EDTA required to titrate is 3.16 mL and the volume of zinc required to titrate is 22.8 mL.

What is molarity?

Molarity is the property of the solution that gives the concentration of the solute present in the solution.

Given,

Mass of cobalt sulfate = 1.697 gm

The molar mass of cobalt sulfate = 155 g/mol

In the first part, the volume of the aliquot is 25 mL and the molarity is 0.08640 M.

The reaction is shown as:

Co²⁺ + H₄Y → CoH₂Y + 2H⁺

Moles of cobalt: n = 0.001694 ÷ 155 = 0.0000109 moles

In 25 ml aliquot moles of cobalt are, 0.000273 moles.

The volume of EDTA solution is calculated as:

V = moles ÷ Molarity

= 0.000273 mole ÷ 0.0864 mol/ L

= 3.16 mL

Hence, 3.16 mL of EDTA is required.

For the second part, moles of EDTA are calculated as:

n = 0.008640 × 0.050 = 4.32 ×10⁻⁴

In a 25 mL, sample moles of EDTA are 2.16 × 10⁻⁴ moles.

Excess moles of EDTA in the solution:

0.000432 - 0.000216 = 0.000216 moles

The volume of EDTA is calculated as:

V = 0.000216 ÷ 0.009450

= 0.0228 L

Hence, 22.8 mL of zinc is required.

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