Qualitative Analysis: Group I General Chemistry 101/102Laboratory ManualUniversity of North Carolina at Wilmington
Safety Considerations • Pb2+ and Hg22+ ions are very toxic. • Wash your hands thoroughly after this experiment. • Place all waste solids and solutions in the appropriately labeled containers in the hood. Qualitative Analysis: Group I • Purpose • To study the chemical properties of Ag+, Pb2+, and Hg22+ ions and the compounds they form. • Use the chemical properties of these ions to identify their presence in an unknown mixture.
General Procedures • Use clean glassware and deionized water to avoid contaminating your sample. • Distinguish between clear, cloudy, colored, and colorless in your descriptions. cloudy yellow clear yellow clear colorless white solid Qualitative Analysis: Group I
Qualitative Analysis: Group I • General Procedures • Exercise caution when using the centrifuge. Use a counterbalance tube. counterbalance sample
General Procedures • Pay attention to whether you are to keep or discard the precipitate and/or supernatant. supernatant precipitate • Use a water bath to heat all mixtures. Qualitative Analysis: Group I
Qualitative Analysis: Group I • Background • Ag+, Pb2+, and Hg22+ ions all form white precipitates with Cl - at room temperature. 6 M HCl AgCl, PbCl2, Hg2Cl2
Pb2+ ions can be precipitated with K2CrO4. PbCrO4 is insoluble in hot and cold water. PbCrO4 Qualitative Analysis: Group I • Background • PbCl2 is insoluble in cold water but soluble in hot water. PbCl2 can be separated from AgCl and Hg2Cl2 by heating the mixture.
Ag+ ions can be precipitated as AgCl by the addition of HNO3. Qualitative Analysis: Group I • Background • When NH3(aq) is added to a mixture of AgCl and Hg2Cl2, the AgCl dissolves and a gray-black mixture of Hg and HgNH2Cl is formed.