Question

A solution is found to be 0.0678% by weight FeCl2. What is the concentration of the Cl1- ion expressed in ppm?

Answer 1

Molar mass of FeCl₂ = 126.751 g/mol
Assume that 0.0678 g of FeCl₂ present in 100 grams of solution and that the density is 1 g/ml, so it is100 mL of solution.
So, the weight of water = 100-.0.0678 = 99.9322 g H2O

.Number of moles of FeCl₂ = 0.0678 g/ 126.751 g/mol = 5.35 x 10^-4 moles of FeCl₂

5.35 x 10^-4 moles of FeCl₂ 2 x 5.35 x 10^-4 moles of of Cl^- ions = 1.07 x 10^-3 moles of Cl^- ions​

1.07 x 10^-3 moles of Cl^- ions​ = 1.07 x 10^-3 x 35.5 g of Cl^- ions = 0.038 g Cl^- ions

0.038 g Cl^- ions = 38 mg Cl^- ions

Concentration of Cl^- ion in the solution, C = m/v where m is the mass of Cl^- ions in mg and v is in L because it is ppm
C = 38 mg / 0.1 L = 380 ppm