When the first portion of 100 mL sample, which is known to contain iron (III) and calcium (II) and whose density is 1.01 g / cm3, is titrated at pH 3.0, 3.5 mL of 0.0100 M EDTA solution is consumed. When the second portion of 100 mL is titrated at pH 10.0, 25.4 mL EDTA solution is consumed. Find the amount of Fe3+ and Ca2+ in this solution as ppm.

Answer 1

Fe.
mols = L x M = 0.003.5 x 0.01 = 0.000035
g Fe = mols Fe x molar mass Fe = 0.000035 x 55.85 = 0.00195 g/100 mL.
That's in 100 mL of 0.1 L so 0.00195/.1 = 0.0195 g/L or 19.5 ppmv(ppm volume)
Since you give a density of the solution I assume you want ppmw (weight/mass) . 19.5 g Fe/101 g soln = 19.3 ppmw.

Ca is done the same way.