Question

I did a EDTA titration in lab. I need to find the amount of zinc in a cough drop which was dissolved in 0.05L of acetate buffer (pH 5.5). It took 0.0235L of EDTA to reach the endpoint. EDTA was 3.78g/L. How do I find the mg of zince in the cough drop?

Answer 1

EDTA reacts with Zn²⁺ in 1:1 ratio, hence the chemical reaction will be as follow,

EDTA + Zn²⁺Zn(EDTA)

No. of moles of EDTA used in titration = No. of moles of Zn²⁺ ions in cough drop

Strength of EDTA = 3.78g in 1L

Strength = Molarity x molecular mass

Molecular mass of EDTA = 292.24g/mol

Molarity of EDTA = Strength / Molecular mass = 3.78/292.24 = 0.012M

No. of moles of EDTA = molarity x volume of solution used = 0.012 x 0.0235 = 0.3 x 10^-3

Mass of Zn in cough drop = 0.3 x 10-3 x 65.38 = 0.0198g