Q1:
Calculate the percentage of iron (MW 55.85) in an unknown sample when 0.2101 g of the sample was dissolved and iron was precipitated as a hydroxide, which upon further ignition and weighing, gave a mass of 0.1107 g as ferric oxide (Fe2O3, MW 159.69).
The reactions are provided below:
Precipitation of iron as a hydroxide: Fe3+ + OH- ? Fe(OH)3 + xH2O
Ignition of hydroxide to form oxide: 2Fe(OH)3-xH2O > Fe2O3 + (x+3)H2O