Complete Question:
A chemist prepares a solution of iron chloride by measuring out 0.10 g of FeCl2 into a 50. mL volumetric flask and filling to the mark with distilled water. Calculate the molarity of anions in the chemist's solution.
Answer:
[Fe+] = 0.0156 M
[Cl-] = 0.0316 M
Explanation:
The molar mass of iron chloride is 126.75 g/mol, thus, the number of moles presented in 0.10 g of it is:
n = mass/molar mass
n = 0.10/126.75
n = 7.89x10⁻⁴ mol
In a solution, it will dissociate to form:
FeCl2 -> Fe+ + 2Cl-
So, the stoichiometry is 1:1:2, and the number of moles of the ions formed are:
nFe+ = 7.89x10⁻⁴ mol
nCl- = 2*7.89x10⁻⁴ = 1.58x10⁻³ mol
The molarity is the number of moles divided by the solution volume, in L (50.0 mL = 0.05 L):
[Fe+] = 7.89x10⁻⁴/0.05 = 0.0156 M
[Cl-] = 1.58x10⁻³/0.05 = 0.0316 M
