Question

5. Extensive heating of 245.2 g of FeCl3 • xH2O produces 137.2 g of FeCl3. a. Calculate the mass of water lost b. Calculate the number of moles of water lost c. Calculate the number of moles of anhydrous salt d. Calculate the mole : mole ratio of salt to water e. Determine the formula for the hydrated salt

Answer 1

5.

a)

mass of water lost = initial mass - final mass = (245.2 - 137.2) g  = 108 g

b)

number of moles of water lost

= mass of water $\times$$\frac{1}{molar\, mass}$

= 108 $\times$$\frac{1}{18(g/mol)}$

= 6

c.

mass of anhydrous salt = 137.2 g

molar mass of FeCl₃ = 56 + 3  $\times$ 35. 5 = 162.5 g/mol

moles of anhydrous salt = 137.2 $\times$_{$\frac{1}{162.5(g/mol)}$} = 0.844

d.

mole ratio of salt to water

= 0.844 : 6

= 1 : 7

e)

Hence formula of the hydrated salt is

FeCl₃ . 7 H₂O