Brown-ring

By the brown ring test with iron(II) sulphate and cold concentrated sulphuric acid. 

When concentrated sulphuric acid is added to a nitrate in the presence of aqueous iron(II) sulphate, the nitrogen oxide liberated forms a brown complex [Fe(H20)5N0] which appears as a brown ring at the acid-aqueous interface (test for a nitrate, p 243). 

C. Further warming to 65°C forms white iron sulfate monohydrate [17375-41 -6], FeSO H2O, which is stable to 300°C. Strong beating results in decomposition with loss of sulfur dioxide. Solutions of iron(II) sulfate reduce nitrate and nitrite to nitric oxide, whereupon the highly colored [Fe(H20) (N0)] ion is formed. This reaction is the basis of the brown ring text for the quaUtative deterrnination of nitrate or nitrite. 

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

FIGURE 46-7 Kayser-Fleischer ring in a young boy with Wilson s disease. The brown ring at the edge of the cornea is due to cornea] copper deposition. Courtesy of Dr Jorge Juncos (Emory University). 

A few drops of the reaction mixture are added to a dilute solution of sodium iodide in glacial acetic acid if a brown ring is not formed, all peroxides have reacted. 

Iron(II) sulfate is a reducing agent. In an aqueous solution, it reduces nitrate and nitrite ions forming a brown ring of Fe(N0)S04. This reaction is applied for qualitative detection of nitrate and nitrite ion in the solution. 

Nitric oxide forms a brown ring in cold ferrous sulfate solution (brown ring test for nitrates). Tbe reaction involves the replacement of a water molecule by nitric oxide in bydrated ferrous ion ... 

Nitrous oxide can be analyzed by GC on a molecular sieve column using a thermal conductivity detector and helium as carrier gas. It may be identified by GC/MS from its mass spectra. The molecular ion is 44. Also, it can be oxidized to NO and identified by the brown-ring test, using FeS04 solution, (see Nitric Oxide.)... 

Certain of the salts in solution have a stronger colour than the acid, and in some cases are more stable thus, a deep blue solution of the copper salt may be obtained by the reduction of nitrosulphonic acid (in sulphuric acid) by mercury in the presence of copper. A suggestion has been made7 that the colour in the brown ring test for a nitrate is due to the formation of the ferrous salt of purple acid, but this is improbable.8... 

The brown-ring test for nitrates involves the formation of a dark-brown unstable complex of nitric oxide and hydrated ferrous ion. The composition of the complex19 is probably [Fe(OH2)8NO]"f+. Let us... 

Acetates may be detected by formation of foul-smelling cacodyl (poisonous) on heating with dry arsenic tiioxide. Other tests for acetate are the lanthanum nitrate test in which a blue or bluish-brown ring forms... 

NC, NG, DEGDN, etc)(Ref 27, pp l347-48)(See also Ref 18a and Charts A B given further in this section). A blue ring test, which is similar to brown ring test described under Reagent G may be used... 

Special test 1. Add iron (II) sulfate, shake, and then add concentrated sulfuric acid produces brown ring 2. White precipitate is formed upon addition of nitron reagent (C20H16N4) test is not specific to only nitrates, however see table of precipitation reagents... 

Silver nitrate Iron (II) sulfate solution (25%, acidified with either acetic or sulfuric acid) White precipitate of silver nitrite A brown ring forms at the junction of the two liquids due to the formation of a complex... 

A sensitive test for nitric oxide is based upon its coordination with Fe2+ ion, giving a dark brown cation Fe(NO)2 f. This cation is the ion which appears in the well-known brown ring test for nitrate after the latter is reduced with excess Fe2+. Nitric oxide forms a large number of coordination compounds, but its behavior does not fit into the same pattern as do the common coordinating agents. Thus, the chemistry of the complexes of... 

Nitrate Add 2 mL of sulfuric acid to 2 mL of a 1 50 aqueous solution, cool, and superimpose 2 mL of ferrous sulfate TS. No brown ring forms at the junction of the two layers. pH of a 1 100 Solution Determine as directed under pH... 

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