Catatan reaksi perbedaan nitrat dan nitrit, mata kuliah Analisis Kimia Farmasi Kualitatif.

1. Nitrat (NO3
-
)
1. Concentrated sulphuric acid: reddish-brown vapours of nitrogen dioxide, accompanied by pungent acid vapours of
nitric acid which fume in the air, are formed on heating the solid nitrate with the reagent. Dilute sulphuric acid has no
action (difference from nitrite).
4NO3
-
+ 2H2SO4 → 4NO2
-
↑ O2↑ + 2SO42-
+ 2H2O
2. Iron (II) sulphate solution and concentrated sulphuric acid (brown ring test): Add 3 ml freshly prepared saturated
solution of iron(II) sulphate to 2 ml nitrate solution, and pour 3-5 ml concentrated sulphuric acid slowly down the side
of the test-tube so that the acid forms a layer beneath the mixture. A brown ring will form where the liquids meet.
The brown ring is due to the formation of the [Fe(NO)]2+
. On shaking and warming the mixture the brown colour
disappears, nitric oxide is evolved, and a yellow solution of iron(III) ions remains.
2NO3
-
+ 4H2SO4 + 6Fe2+
→ 6Fe3+
+ 2NO↑ + 4SO4
2-
+ 4H2O
Fe2+
+ NO↑ → [Fe(NO)]2+
3. Sulphanilic acid – α-naphthylamine reagent (Reduction to nitrite tes): A Nitrates are reduced to nitrites by metallic
zinc in acetic acid solution ; the nitrite can be readily detected by means of the sulphanilic acid – α-naphthylamine
reagent. Mix on a spot plate a drop of the neutral or acetic acid test solution with a drop of the sulphanilic acid reagent
and a drop of the α-naphthylamine reagent,and add a few milligrams of zinc dust. A red colouration develops.
Nitrit (NO2
-
)
1. Dilute hydrochloric acid: Cautious addition of the acid to a solid nitrite in the cold yields a transient, pale-blue liquid
(due to the presence of free nitrous acid, HNO2 ,or its anhydride, N2O3 ) and the evolution of brown fumes of nitrogen
dioxide, the latter being largely produced by combination of nitric oxide with the oxygen of the air. Similar results are
obtained with the aqueous solution.
NO2
-
+ H+
→ HNO2
(2HNO2 → H2O + N2O3)
3HNO2 → HNO3 + 2NO↑ + H2O
2NO↑ + O2↑ → 2NO2↑
2. Iron(II) sulphate solution (brown ring test): When the nitrite solution is added carefully to a concentrated (25 %)
solution of iron(II) sulphate acidified with dilute acetic acid or with dilute sulphuric acid, a brown ring, due to the
compound [Fe,NO]SO4,is formed at the junction of the two liquids. If the addition has not been made cautiously, a
brown colouration results. This reaction is similar to the brown ring test for nitrates, for which a stronger acid
(concentrated sulphuric acid) must be employed.
NO2- + CH3COOH → HNO2 + CH3COO-
3HNO2 → H2O + HNO3 + 2NO↑
Fe2+ + SO42- + NO↑ → [Fe,NO]SO4
3. Sulphanilic acid – α-naphthylamine reagent: Place a drop of the neutral or acid test solution on a spot plate and mix it
with a drop of the sulphanilic acid reagent, followed by a drop of the a-naphthylamine reagent. A red colour is formed.
Nitrat (NO3
-
) Nitrit (NO2
-
)
1. Hanya bereaksi dengan H2SO4 p. 1. Bereaksidengan H2SO4.
+ H2SO4 p → ↑ merah-kecoklatan. + H2SO4 p → larutan biru-pucat dan ↑ coklat.
2. Harus ditambahkan H2SO4 p. 2. Tidak perlu ditambahkan H2SO4 p
+ H2SO4 p + Fero(II) sulfat → cincin coklat → .+ Fero(II) sulfat → cincin coklat →
(dikocok lebih lanjut) larutan kuning (ditambahkan pereaksi berlebih) larutan coklat
3. Harus ditambahkan serbuk Zn. 3. Tidak perlu serbuk Zn.
+ as. sulfanilat + reagen α-naftilamin + serbuk Zn + as. sulfanilat + reagen α-naftilamin
→ larutan merah → larutan merah

2. Sulfat (SO42-)
1. Sodiumrhodizonate test
2. 8uMercury(II) nitrate solution
Sulfit (SO32-)