Question

A chemist prepares a solution of iron chloride by measuring out of into a volumetric flask and filling to the mark with distilled water. Calculate the molarity of anions in the chemist's solution.

Answer 1

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