Question

a 5.49g sample of iron(iii) chloride hydrate was found to contain 2.20g of water. what is the complete formula of the hydrate?

Answer 1

we are given the mass of the hydrate and the mass of the water present. In this case, the mass of anhydrous iron iii chloride is equal to 3.29 grams. This means the mass percent of anhydrous part is 60 percent. The mass ratio of anhydrous to hydrate is equal to 162.2 g / x where x is the molar mass of the hydrate. x then is equal to 270. 66 g/mol. Hence the total molar mass of water is equal to 108. 46 g/mol equal to about 6 moles of H20. The molecular formula hence is FeCl3 - 6H2O

Answer 2

Answer: FeCl₃ . 6H₂O,

Step-by-step explanation:

1) The chemical formula of iron(III) chloride is FeCl₃ (the oxidation number of Fe is 3+, and the oxidation number of Cl is 1-).

2) The formula that you are lookin for the hydrate is of the type FeCl₃ . n H₂O, where n is the number of water molecules per each unit formula of Fe₂O₃.

3) Find the mass of anhydrous FeCl₃ by difference:

mass of FeCl₃ = mass of the sample - mass of the water in the sample

mass of FeCl₃ = 5.49g - 2.20 g = 3.29 g

4) Convert the mass of FeCl₃ in number of moles

number of moles = mass in grams / molar mass

molar mass of FeCl₃ = 55.845 g/mol + 3×35.453 g/mol = 162.204 g/mol

number of moles = 3.29 g / 162.204 g/mol = 0.0203 mol FeCl₃

5) Convert the mass of water in number of moles:

molar mass of water = 18.015 g/mol

number of moles of water = mass in grams / molar mass = 2.20 g / 18.015 g/mol = 0.122 moles H₂O

6) Find the mole ratio of water to iron chloride:

0.122 mol water / 0.0203 mol iron chloride = 6.01 ≈ 6

Therefore, the complete formula of the hydrate is FeCl₃ . 6H₂O,