Question

12 diet supplement pills have a total mass of 16.2g. the pills are ground to a powder dissolved in a suitable aqueous solvent, and precipitated with aqueous ammonia to form iron (II) and iron (III) hydroxides. the precipitate is filtered and ignited in a furnace to form 456mg of Fe2O3. the mean iron content per pill is.?

Answer 1

Ans. Total Fe₂O₃ obtained = 456 mg = 0.456 g                           ; [1 g = 1000 mg]

Moles of Fe₂O₃ = Mass/ Molar mass

                                    = 0.456 g / (159.6922 g/mol)

                                    = 0.0028555 mol

Note that 1 mol Fe₂O₃ has 2 Fe-atoms. Thus, 1 mol Fe₂O₃ is equivalent to 2 mol Fe-atom.

So, moles of Fe-atom = 2 x moles of Fe₂O₃

= 2 x 0.0028555 mol

= 0.005711 mol

Total mass of Fe in 12 pills = Moles x Molar mass

                                    = 0.005711 mol x (55.847 g/mol)

                                    = 0.318942217 g

Mean Fe-content per pill = Total Fe-content / 12 pills

                                    = 0.318942217 g/ 12 pills

                                    = 0.0265785 g/pill

                                    = 26.58 mg/ pill

Thus, mean Fe-content = 26.58 mg/ pill