Qualitative analysis, a branch of analytical chemistry, deals with the identity of a substance found in a given sample, and not the amount of substance in it. It only concerns the substances present or absent in a given sample. Qualitative analysis is therefore used to determine unknown ions present in chemical samples by observing and analyzing results from various reactions of the sample with chemicals.
Qualitative analysis is done through a series of steps. It is usually divided into two parts, namely: the preliminary and confirmatory tests. Preliminary tests are done to eliminate ion choices, while confirmatory tests are done to confirm the actual ions present in the sample.
Qualitative analysis was done to identify the ions present in a given unknown solution. In this experiment, the qualitative traits of chemicals and their corresponding chemical reactions with other chemicals were more evident and familiar. Five preliminary tests were used to infer possible ions: two for cations, namely, precipitation reactions with hydroxide (OH-) and ammonia (NH3) respectively; and two for anions, namely, precipitation reactions with barium nitrate (Ba(NO3)2), and non-precipitation reactions involving ferric chloride (FeCl3) and potassium permanganate (KMnO4) respectively. Confirmatory tests for all possible ions were also used to confirm the suspected ions from the preliminary tests. The experimentation was repeated thrice. Observed changes were recorded and compared to controlled results from previous studies.
Results of the preliminary and confirmatory tests have shown that the solution contained calcium (Ca2+), ammonium (NH4+) and thiocyanate (SCN-) in all replications.
Keywords: unknown analysis, cations, anions, calcium, ammonium, thiocyanate, preliminary tests, confirmatory tests
Analytical chemistry has two divisions, namely: qualitative analysis and quantitative analysis. Qualitative analysis concerns the identity of a substance found in a given sample (i.e. ion composition of a substance in a sample). Quantitative analysis concerns the amount of substance present in a given sample. (Larson, 2008)
Qualitative analysis is used to identify unknown substances (i.e. cations and anions) by observing and analyzing results from various reactions of the sample with other chemicals. These results can be compared to controlled results from previous studies. Qualitative analysis is done through a step-by-step reaction process, with each notable change in each step affecting which step to go next. It is usually done in two parts, namely, the preliminary tests and confirmatory tests.
Preliminary tests are primarily conducted to eliminate possible ion choices that do not have characteristic traits for the specific reaction conducted. Confirmatory tests, on the other hand, are conducted after eliminating ion choices. These tests are used to confirm the specific ions present in the given solution.
Preliminary Tests for Cations
Two (2) test tubes were prepared for the preliminary tests for cations. Five (5) drops of the given sample were placed in each test tube. One (1) drop of 1M sodium hydroxide (NaOH) was added in a test tube containing the sample. Changes in color and precipitate were recorded. Excess sodium hydroxide (NaOH) was added into the same test tube. Dissolution of precipitate and color change were noted.
In another test tube prepared, One (1) drop of 1M ammonia (NH3) was added. Changes in color and precipitate were recorded. Excess ammonia (NH3) was added into the same test tube. Dissolution of precipitate and color change were noted.
Confirmatory Tests for Cations
Five (5) test tubes were prepared for the confirmatory tests for cations. five (5) drops of the given sample were placed in each test tube. In order to determine if Iron (III) ions (Fe3+) were present in the sample, two (2) test were done. First, two (2) drops of 0.1 M potassium...
References: Larson, L. (2008). Introduction to Qualitative Analysis. Retrieved August 27, 2012 from http://www.foothill.edu/attach/psme/sinha.QualDiscussion.pdf.
UP Chemistry Alumni Foundation. (2006). General Chemistry Laboratory Manual. 5th ed. p. 51-55.
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