The main objective of this experiment is to carry out qualitative analysis to identify metal cations in unknown solution 1. INTRODUCTION
An unknown material can be determined by using simple chemical tests and separations which is called as inorganic qualitative analysis. The separation of cations depends on the difference in their propensity to form precipitates. Separation scheme is used to classify cation into five groups on the basis of their physical and chemical behavior opposed to some reagents. Classification is based on whether there is formation of precipitates or not when metal cations react with the reagent. The five groups of cations and the characteristics of these groups are as follows: i. Group I
Ag+, Hg+, Pb+
This group I cations form precipitate when reacted with HCl. ii. Group II
As3+, Bi3+, Cd3+, Cu2+, Hg2+, Pb2+, Sn4+
This group II cations form precipitate when reacted with H2S in acidic condition. iii. Group III
Co3+, Fe2+, Mn2+,Ni2+, Zn2+, *Al3+, Cr3+
This group III cations form precipitate when reacted with H2S in basic condition. *Al3+ is separated as Al(OH)3
iv. Group IV
Ba2+, Ca2+, Mg2+, Sr2+
This group IV cations form precipitate when reacted with (NH4)2CO3. v. Group V
This group V cations form soluble salts when reacted with (NH4)2CO3. The principle of periodicity applied to the results of this series of experiments. It helps, in trying to see the periodic pattern, to know the pattern that results when we do a separation and analysis of all metal ions.
1. 2 drops of 6 M HCl was added to 1 ml of the mixture of the metal cations. 2. The suspension was centrifuged for 1 minute as ppt. of chloride was formed. 3. 1 additional drop of 6 M HCl was added to the clear supernatant to check for complete precipitation. 4. The supernatant was centrifuged again for 1 minute as the ppt. was observed again. 5. The supernatant was decanted in a clean test tube.
6. The supernatant was saved for the procedure B.
1. 6 M NH3 was added drop wise to the solution until basic.
2. The sample was placed in a boiling water bath for 2-3 minutes to remove excess NH3. 3. The volume of the solution was adjusted to 2 ml with distilled water and 10 drops of 6 M HCl was added. 4. 12 drops of thioacetamide was added to the solution and stirred. 5. The sample was heated in a boiling water bath for 10 minutes to allow for the hydrolysis of thioacetamide producing H2S. 6. The sample was centrifuged for 2 minutes as the ppt. of sulfide was formed. The supernatant was the decanted to a clean test tube. 7. The supernatant was saved for Procedure C.
1. 3 additional drops of 1 M thioacetamide was added to the supernatant and was reheated for 5 more minutes to test complete precipitation. 2. As the ppt. was formed, the supernatant was centrifuged and decanted into a clean test tube and the ppt. was discarded 3. The volume of the solution was adjusted to 3 ml with distilled water and 10 drops of 6 M HCl and 10 drops of 6 M NH3 was added. 4. 6 M NH3 was added drop wise until the solution became basic. 5. 5 additional drops of 6 M NH3 and 12 drops of 1 M thioacetamide were added and the mixture was stirred thoroughly. 6. The sample was heated in a boiling water bath for 10 minutes. 7. The supernatant was centrifuged and decanted as the ppt. was formed. 8. The supernatant was saved for procedure D.
1. 6 M NH3 was added drop wise until the solution became basic. 2. 10-15 drops of 6 M NH3 was added to buffer the solution.
3. 20-30 drops of (NH4)2CO3 was added to the sample and stirred. 4. The test tube containing the ppt. of carbonate was transferred to a warm water bath of 70-80OC for 2-3 minutes. 5. The mixture was centrifuged and the supernatant was decanted after the sample had been warmed. 6. The ppt. was saved for Procedure D(i).
1. The ppt. was washed with 2 ml of distilled water then the wash water was...
References: 1. Group IV Analysis. (n.d.). Retrieved from Cations Forming Insoluble Carbonates: http://isite.lps.org/mschmid3/web/documents/GroupIVanalysis.pdf
2. Inorganic Chemistry. (n.d.). Retrieved from Classification of the Cations and Anions: http://www.inc.bme.hu/en/subjects/inchem/sillabus/129-145.pdf
3. Leong, O. H. (2009). Qualitative Analysis. In Know Your 'O ' Level Chemistry (pp. 101-103). Singapore: Panpac Education Pte Ltd.
4. William L. Masterton, C. N. (2006). Quaitative Analysis. In Chemistry: Principles and Reactions, Updated Edition (pp. 436-437). Thomson Brooks/ Cole.
5. Wulfsberg, G. (2000). Application of HSAB: The Qualitative Analysis Scheme for Metal Ions. In Inorganic Chemistry (pp. 209-211). Sausalito: University Science Book.
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