Gravimetric Analysis

Example #1:

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)   +SO₄^2– (aq)

Example #2: The Fe in a 1.1530 g sample of iron ore is precipitated as Fe₂O_{3 *} 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) → Fe₂O_{3 *} x H₂O

Fe₂O_3 * 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