Question

A buffer solution containing calcium ion, Ca^2+, was titrated to the endpoint using 38.71mL of 0.2589 M EDTA. how many moles of ca^2+ were present in the solution?

Answer 1

Given the concentration of EDTA = 0.2589 M

volume of EDTA = 38.71 mL = 38.71mL x (1L / 1000 mL) = 0.03871 L

Hence moles of EDTA required for complete titraton = MxV = 0.2589 M x 0.03871 L = 0.0100 mol

The chemcial reaction for the reaction of Ca²⁺ with EDTA is

Ca²⁺(aq) + EDTA^4-(aq) ----- > Ca(EDTA)^2-(aq)

1 mol ------- 1 mol ----------------- 1 mol

Hence equal moles of Ca²⁺(aq) + EDTA react with each other.

Hence moles of Ca²⁺ present in the solution = moles of EDTA reacted = 0.0100 mol (answer)