Question

49.00 ml solution involve Ca2+ is and it is titrated with 0.0149 M of EDTA, which need 12.70 mL of EDTA to hit the end point.

1. find the concentration of Ca²⁺ in ppm
2. For this titration find an reasonable pH condition with explanation.
3. Advise a method to find out the end point of this titration.

Answer 1

Volume of Ca2+(V2) = 49.0 mL

Volume of EDTA (V1) = 12.70 mL

Molarity of EDTA (M1) = 0.0149M

Molarity of Ca2+ (M2) =?

To find the concentration of Ca2+, we use the relation,

M1V1 = M2V2

M2 = (M1V1) / V2

M2 = (12.70 × 0.0149) / 49

=  0.00386 M

= 0.00386 × 1000 ppm

= 3.86 ppm

This titration is carried in a pH of 10, in a buffer of NH3-NH4+(NH4-NH4 is used as a buffer to maintain constant pH) , which keep the EDTA in half neutralized form. It prevents the reaction of impurity cations like Fe2+ in water and readily allow to react with Ca2+ (group llA ions)

Titration :-

Pipette a 10 mL of the sample solution into a conical flask. Add 40 mL of distilled water and 4ml of 8 mol /L sodium hydroxyde solution and allow solution to stand for about 5 minutes with occasional swirling a small of magnesium hydroxide may precipitate during this time. Add 0.1 gram of Patton-Reader indicator and swirl the solution dissolve the indicator. Titration the sample with EDTA solution. The end point is a colour change from pink to blue. Repeat the titration with further samples to get concordant results.