CHEM122L Lab Report III - Analysis of Group II Cations Kristine Cecille C Isidro Author Abstract This laboratory activity aims to observe a series of

CHEM122L Lab Report III - Analysis of Group II Cations...

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Analysis of Group II Cations Kristine Cecille C. Isidro Author Abstract: This laboratory activity aims to observe a series of precipitation reactions to determine and confirm the presence of Group II cations Pb 2+ , Cu 2+ , Hg 2+ , Sn 2+ , and Bi 3+ using a qualitative analysis scheme. A solution containing all five (5) Group II cations was prepared and treated to deduce and yield some of the properties of the said cations, leading to the determination of each. The solution was first treated with 4M nitric acid and heated gently over until an adequate amount remained. The residue was cooled down and added with 10 drops of water. It was then made basic by adding 1M aqueous ammonia and later made acidic with 6M hydrochloric acid. Moreover, it was treated with 5% thioacetamide solution and placed in a hot bath for ten (10) minutes to get complete precipitation with Group II sulfides. The mixture was then decanted and the precipitate was further treated with 4M sodium hydroxide and 5% thioacetamide solution and again placed in a hot bath for another five (5) minutes. The resulting mixture was then centrifuged and decanted. The precipitate and the solution were then treated and made to react within a series of procedures to identify and determine the presence of + , Cu 2+ , Hg 2+ , Sn 2+ , and Bi 3+ . Keywords: Group II cations, precipitation reaction, precipitate, supernatant, decant, qualitative analysis scheme, solubility, thioacetamide solution Introduction: One of the wide-scope fields of a chemist is the determination and analysis of substances for composition, particularly those involved in precipitation reactions. However, with hundreds of elements and compounds, as well as thousands of probable combinations, it can be a very difficult task. Observations and knowledge upon the identity of the “unknown” is therefore important, and qualitative analysis provides a starting point in the analysis and determination of the presence of certain substances. I. Preparation of the setup A test tube containing the Group II cations Pb 2+ , Cu 2+ , Hg 2+ , Sn 2+ , and Bi 3+ was prepared, added with five (5) drops of 4M nitric acid and heated directly over a low flame. It was then cooled down and added with ten (10) drops of water. 1M aqueous ammonia was then added drop by drop until it was basic to litmus. It was later made acidic by treatment with 6M hydrochloric acid. Moreover, it was treated with 5% thioacetamide solution and placed in a hot bath for ten (10) minutes. Afterwards, one (1) mL of water was added and placed in a hot bath for another five (5) minutes. The mixture was then decanted and the precipitate was saved.
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II. Treatment of the precipitate from Procedure I The precipitate containing Pb 2+ , Cu 2+ , Hg 2+ , Sn 2+ , and Bi 3+ cations was treated with twelve (12) drops of 4M sodium hydroxide, four (4) drops of thioacetamide solution, and placed in a hot bath for five (5) minutes. Through centrifugation, the precipitate was thoroughly separated from the solution and both were placed in separate test tubes. The precipitate was again added with twelve (12) drops of 4M sodium
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