The presence of iron ions in drinking water can cause discoloration of the water, a change in taste, darkening of prepared foods, and, in some cases health problems. A slow and uniform precipitation of iron, as Fe(OH)3 can be used as a gravimetric analysis technique. This can be facilitated when the precipitating OH- is generated within the solution using urea decomposition: H2NCONH + H2O CO2 + 2 NH3 The NH3 generated converts to OH- via this reaction: H2O + NH3 NH4+ + OH-
(A) A solution containing 1.80 x 10-3 M Fe3+ is treated with urea to precipitate the Fe3+ as Fe(OH)3. What molarity of urea is needed to precipitate the iron if a 30% excess of urea is desired? ______ M urea
(B) The Fe(OH)3 produced by the process described above is gelatinous so is ignited to convert it to Fe2O3. What is the percent of iron in a solution if 100.0 grams of the solution yielded, upon proper treatment, 0.715 grams of Fe2O3? Note first determine the gravimetric factor for this precipitation.
Gravimetric factor = _______
Mass percent Fe = _______%