Phosphate Radical - Phosphate Test

Theoretical Background / Context

Qualitative Chemical Analysis: 

• Branch of chemistry that deals with the identification of elements or grouping of elements present in a sample.
• The techniques employed in qualitative analysis vary in complexity, depending on the nature of the sample. 
• In some cases, it is necessary only to verify the presence of certain elements or groups for which specific tests applicable directly to the sample (e.g., flame tests, spot tests in inorganic analysis) may be available. 
• More often the sample is a complex mixture, and a systematic analysis must be made in order that all the constituents may be identified. 
• It is customary to classify the methods into two classes: 

1. qualitative inorganic analysis 
2. qualitative organic analysis.

• The sample is commonly dissolved in water for the determination of anionic constituents (i.e., negatively charged elements or groupings of elements) and cationic constituents (i.e., positively charged elements or groupings of elements). 
• The procedure followed is based on the principle of treating the solution with a succession of reagents so that each reagent separates a group of constituents. 
• The groups are then treated successively with reagents that divide a large group into subgroups or separate the constituents singly. 
• When a constituent has been separated it is further examined to confirm its presence and to establish the amount present (quantitative analysis). 
• Portions of the material are dissolved separately, and different procedures are used for each to detect the cationic and anionic constituents.
• Some phosphate rock is used to make calcium phosphate nutritional supplements for animals. 
• Pure phosphorus is used to make chemicals for use in industry. 
• The most important use of phosphate rock, though, is in the production of phosphate fertilizers for agriculture.

Principle of Work

• The purpose of the phosphate test experiment is the identification of phosphate through the following steps:

1) Physical examination

2) Solubility testing.

3) Reaction with barium chloride (Phosphate precipitation test).

4) Confirmatory test with silver nitrate.

5) Phosphate confirmatory test with ferric chloride.

6) Confirmatory test with ammonium molybdate (ammonium molybdate phosphate test).

7) Confirmatory test with magnesia mixture.

• These sequential steps provide a reliable phosphate analysis