Summary of "Brown ring test for nitrate ions NO3- . Formation of [Fe(H2O)5(NO)]SO4"
Summary of the Brown Ring Test for Nitrate Ions (NO3⁻) and Formation of [Fe(H2O)5(NO)]SO4
The Brown Ring Test is a qualitative chemical test used to detect the presence of nitrate ions (NO3⁻) in a solution by forming a distinctive brown ring complex.
Main Ideas and Concepts
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Purpose: To test for nitrate ions using the Brown Ring Test.
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Chemicals Used:
- Sodium nitrate (source of nitrate ions)
- Ferrous sulfate (FeSO4)
- Concentrated sulfuric acid (H2SO4)
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Procedure:
- Mix sodium nitrate with ferrous sulfate solution.
- The test is very sensitive; even diluted mixtures with 1–2 cm³ of water still give positive results.
- Carefully add concentrated sulfuric acid down the side of the test tube to form a separate, denser layer at the bottom without mixing.
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Chemical Reaction:
- In the acidic environment provided by concentrated sulfuric acid, nitrate ions act as oxidizing agents.
- Ferrous ions (Fe²⁺) act as reducing agents, reducing nitrate ions to nitrogen monoxide (NO).
- Ferrous ions also act as indicators by forming a brown complex with nitrogen monoxide.
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Observation:
- A brown ring forms at the interface between the acid and the solution layers.
- The brown complex is identified as pentaaquanitril iron(II) sulfate, [Fe(H2O)5(NO)]SO4.
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Additional Notes:
- The brown ring may be difficult to see initially; adjusting the test tube vertically and shaking gently helps visualize it clearly.
- The reaction involves removal of spectator ions to simplify the ionic equation.
Detailed Methodology / Instructions
- Take a solution containing nitrate ions (e.g., sodium nitrate).
- Add ferrous sulfate solution to the nitrate solution.
- Optionally dilute the mixture with 1–2 cm³ of water if needed; the test remains sensitive.
- Carefully add concentrated sulfuric acid along the side of the test tube to form a separate bottom layer.
- Observe the formation of a brown ring at the interface between the acid and the solution.
- Tilt the test tube vertically and gently shake if the ring is not immediately visible.
- Confirm the presence of nitrate ions by the formation of the brown complex [Fe(H2O)5(NO)]SO4.
Speakers / Sources
- Serg (the presenter of the chemistry tutorial)
Category
Educational
