If you were given an unknown solution, write the steps that would be needed to prove that a solution contained phosphate.
This really is too general (too open ended). If the solution may contain any anion, one must assure that arsenate and arsenite are not present, then test with ammonium molybdate. If arsenate or arsenite are present, arsenate must be reduced with sodium sulfite, then pptd as As2S3 with H2S. After the excess H2S gas is expelled, perform the ammonium molybdate test.
To prove the presence of phosphate in an unknown solution, you can follow these steps:
1. Start by preparing a set of reagents:
a. Ammonium molybdate solution: Dissolve 10 g of ammonium molybdate tetrahydrate in 100 ml of distilled water.
b. Nitric acid solution: Mix equal parts of concentrated nitric acid and distilled water.
c. Ammonium hydroxide solution: Dilute concentrated ammonium hydroxide with distilled water.
2. Take a small sample of the unknown solution in a test tube.
3. Add a few drops of nitric acid to the solution in the test tube. This step helps in preventing the formation of any interfering substances.
4. Heat the test tube gently over a Bunsen burner or a heating source to evaporate any excess liquid. This step is crucial to ensure that the final result is reliable.
5. Once the solution has evaporated or reduced down to a smaller volume, allow it to cool.
6. Add a few milliliters of ammonium molybdate solution to the cooled sample in the test tube. Ensure that the solution covers the entire sample.
7. Mix the contents of the test tube well by shaking it gently.
8. Slowly add a few milliliters of ammonium hydroxide solution drop by drop into the test tube while continuously shaking. This step helps to reduce any excess acidity.
9. Observe the solution in the test tube. If a yellow precipitate forms, it indicates the presence of phosphate in the unknown solution. The yellow precipitate is ammonium phosphomolybdate, a characteristic indicator of phosphate ions.
10. To confirm the presence of phosphate, filter the solution to separate the precipitate. Wash the precipitate with distilled water to remove any impurities.
11. Evaporate the filtered solution to dryness to obtain the pure ammonium phosphomolybdate precipitate.
12. Finally, perform further confirmatory tests, such as spectroscopic analysis or elemental analysis, to identify the compound as phosphate.
Remember to handle all chemicals and laboratory equipment with care, use appropriate protective measures, and follow safety protocols while conducting experiments.