In Gravimetric Analysis the mass of a product in a chemical reaction is used to calculate the amount of the original analyte.
A 25.00 mL solution containing Br – was treated with excess PbSO4 to precipitate 0.7550 g of PbBr2. What was the molarity of the Br – in the unknown?
PbSO4 (s) + 2 Br – (aq) → PbBr2 (s) +SO42– (aq)
Example #2: The Fe in a 1.1530 g sample of iron ore is precipitated as Fe2O3 * x H2O by the addition of NH3. The residue is ignited at high temperatures to give 0.6310 g of pure Fe2O3. Calculate the weight percent of Fe in the ore.
2 Fe3+ (aq) + 6 OH– (aq) → Fe2O3 * x H2O
Fe2O3 * xH2O + heat → Fe2O3 + 6 x H2O
Example #3: The reaction between piperazine and acetic acid creates an adduct product known as piperazine diacetate.
A 7.50 g sample of impure piperazine contained 83.01% piperazine. How many grams of piperazine diacetate would be formed in the process?
Example #4: The amount of iron within an ore sample was determined by an oxidation-reduction titration using potassium permanganate, KMnO4, as the titrant. A 0.5600 g sample of the ore was placed into acid and the newly freed Fe3+ was then reduced to Fe2+. The titration of this solution required 39.82 mL of 0.0315 M KMnO4 to reach the end-point. Determine the mass percent of Fe2O3 in the sample.
MnO4– +5 Fe2+ + 8 H+ → Mn2+ + 5 Fe3+ + 4 H2O