Analytical Chem istry - DePauw University

Chapter 8 Gravimetric Methods373Table 8.1 Selected Precipitation Gravimetric Methods for InorganicCations and Anions (Arranged by Precipitant)Analyte Precipitant Precipitate Formed Precipitate WeighedBa 2+ (NH 4 ) 2 CrO 4 BaCrO 4 BaCrO 4Pb 2+ K 2 CrO 4 PbCrO 4 PbCrO 4Ag + HCl AgCl AgCl2+Hg 2 HCl Hg 2 Cl 2 Hg 2 Cl 2Al 3+ NH 3 Al(OH) 3 Al 2 O 3Be 2+ NH 3 Be(OH) 2 BeOFe 3+ NH 3 Fe(OH) 3 Fe 2 O 3Ca 2+ (NH 4 ) 2 C 2 O 4 CaC 2 O 4 CaCO 3 or CaOSb 3+ H 2 S Sb 2 S 3 Sb 2 S 3As 3+ H 2 S As 2 S 3 As 2 S 3Hg 2+ H 2 S HgS HgSBa 2+ H 2 SO 4 BaSO 4 BaSO 4Pb 2+ H 2 SO 4 PbSO 4 PbSO 4Sr 2+ H 2 SO 4 SrSO 4 SrSO 4Be 3+ (NH 4 ) 2 HPO 4 NH 4 BePO 4 Be 2 P 2 O 7Mg 2+ (NH 4 ) 2 HPO 4 NH 4 MgPO 4 Mg 2 P 2 O 7Zn 2+ (NH 4 ) 2 HPO 4 NH 4 ZnPO 4 Zn 2 P 2 O 7Sr 2+ KH 2 PO 4 SrHPO 4 Sr 2 P 2 O 7CN – AgNO 3 AgCN AgCNI – AgNO 3 AgI AgIBr – AgNO 3 AgBr AgBrCl – AgNO 3 AgCl AgCl–ClO 3 FeSO 4 /AgNO 3 AgCl AgClSCN – SO 2 /CuSO 4 CuSCN CuSCN2–SO 4 BaCl 2 BaSO 4 BaSO 4Or g a n i c An a l y s i sSeveral organic functional groups or heteroatoms can be determined usingprecipitation gravimetric methods. Table 8.4 provides a summary of severalrepresentative examples. Note that the procedure for the determination ofalkoxy functional groups is an indirect analysis.Qu a n t i t a t i ve Ca l c u l at i o n sThe stoichiometry of a precipitation reaction provides a mathematical relationshipbetween the analyte and the precipitate. Because a precipitationgravimetric method may involve several chemical reactions before the precipitationreaction, knowing the stoichiometry of the precipitation reaction