Editing Qualitative inorganic analysis (section)

==Detecting anions==

=== 1st analytical group of anions ===
The ''1st group of anions'' consist of [[Carbonate|CO{{su|b=3|p=2&minus;}}]], [[Bicarbonate|HCO{{su|b=3|p=&minus;}}]], [[Acetate|CH<sub>3</sub>COO<sup>&minus;</sup>]], [[Sulfide|S<sup>2&minus;</sup>]], [[Sulfite|SO{{su|b=3|p=2&minus;}}]], [[Thiosulfate|{{chem|S|2|O}}{{su|b=3|p=2&minus;}}]] and [[Nitrite|NO{{su|b=2|p=&minus;}}]]. The reagent for Group 1 anions is dilute hydrochloric acid (HCl) or dilute sulfuric acid (H<sub>2</sub>SO<sub>4</sub>).

* Carbonates give a brisk effervescence with dilute H<sub>2</sub>SO<sub>4</sub> due to the release of CO<sub>2</sub>, a colorless gas which turns [[limewater]] milky due to formation of CaCO<sub>3</sub> ([[carbonatation]]). The milkiness disappears on passing an excess of the gas through the lime water, due to formation of Ca(HCO<sub>3</sub>)<sub>2</sub>.
* Acetates give the vinegar-like smell of CH<sub>3</sub>COOH when treated with dilute H<sub>2</sub>SO<sub>4</sub> and heated. A blood red colouration is produced upon addition of yellow FeCl<sub>3</sub>, due to formation of [[iron(III) acetate]].
* Sulfides give the rotten egg smell of H<sub>2</sub>S when treated with dilute H<sub>2</sub>SO<sub>4</sub>. The presence of sulfide is confirmed by adding [[lead(II) acetate]] paper, which turns black due to the formation of PbS. Sulfides also turn solutions of red [[sodium nitroprusside]] purple.
* Sulfites produce SO<sub>2</sub> gas, which smells of burning sulfur, when treated with dilute acid. They turn acidified K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> from orange to green.
* Thiosulfates produce SO<sub>2</sub> gas when treated with dilute acid. In addition, they form a cloudy precipitate of [[sulfur]].
* Nitrites give reddish-brown fumes of NO<sub>2</sub> when treated with dilute H<sub>2</sub>SO<sub>4</sub>. These fumes cause a solution of [[potassium iodide]] (KI) and [[starch]] to turn blue.

=== 2nd analytical group of anions ===
The ''2nd group of anions'' consist of [[Chloride|Cl<sup>&minus;</sup>]], [[Bromide|Br<sup>&minus;</sup>]], [[Iodide|I<sup>&minus;</sup>]], [[Nitrate|NO{{su|b=3|p=&minus;}}]] and [[Oxalate|C{{su|b=2}}O{{su|b=4|p=2&minus;}}]]. The group reagent for Group 2 anion is concentrated sulfuric acid (H<sub>2</sub>SO<sub>4</sub>).

After addition of the acid, chlorides, bromides and iodides will form precipitates with [[silver nitrate]]. The precipitates are white, pale yellow, and yellow, respectively. The silver halides formed are completely soluble, partially soluble, or not soluble at all, respectively, in aqueous ammonia solution.

Chlorides are confirmed by the ''[[chromyl chloride]] test''. When the salt is heated with K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> and concentrated H<sub>2</sub>SO<sub>4</sub>, red vapours of chromyl chloride (CrO<sub>2</sub>Cl<sub>2</sub>) are produced. Passing this gas through a solution of NaOH produces a yellow solution of [[sodium chromate|Na<sub>2</sub>CrO<sub>4</sub>]]. The acidified solution of Na<sub>2</sub>CrO<sub>4</sub> gives a yellow precipitate with the addition of [[lead(II) acetate|(CH<sub>3</sub>COO)<sub>2</sub>Pb]].

Bromides and iodides are confirmed by the ''layer test''. A sodium carbonate extract is made from the solution containing bromide or iodide, and [[chloroform|CHCl<sub>3</sub>]] or [[carbon disulfide|{{chem|CS|2}}]] is added to the solution, which separates into two layers: an orange colour in the {{chem|CHCl|3}} or {{chem|CS|2}} layer indicates the presence of Br<sup>&minus;</sup>, and a violet colour indicates the presence of I<sup>&minus;</sup>.

Nitrates give brown fumes with concentrated H<sub>2</sub>SO<sub>4</sub> due to formation of NO<sub>2</sub>. This is intensified upon adding copper turnings. Nitrate ion is confirmed by adding an aqueous solution of the salt to FeSO<sub>4</sub> and pouring concentrated H<sub>2</sub>SO<sub>4</sub> slowly along the sides of the test tube, which produces a brown ring around the walls of the tube, at the junction of the two liquids caused by the formation of {{chem|Fe(NO)|2+}}.<ref>{{cite book
| title = University Chemistry, Volume 1
| author = C. Parameshwara Murthy
| publisher = New Age International
| year = 2008
| isbn = 978-81-224-0742-6
| page = 133
}}</ref>

Upon treatment with concentrated sulfuric acid, oxalates yield colourless CO<sub>2</sub> and CO gases. These gases burn with a bluish flame and turn lime water milky. Oxalates also decolourise KMnO<sub>4</sub> and give a white precipitate with CaCl<sub>2</sub>.

=== 3rd analytical group of anions ===
The ''3rd group of anions'' consist of [[Sulfates|SO{{su|b=4|p=2&minus;}}]], [[Phosphates|PO{{su|b=4|p=3&minus;}}]] and [[Borates|BO{{su|b=3|p=3&minus;}}]]. They react neither with concentrated nor diluted H<sub>2</sub>SO<sub>4</sub>.

* Sulfates give a white precipitate of BaSO<sub>4</sub> with BaCl<sub>2</sub> which is insoluble in any acid or base.
* Phosphates give a yellow crystalline precipitate upon addition of HNO<sub>3</sub> and [[ammonium heptamolybdate|ammonium molybdate]] and heating the solution.
* Borates give a green flame characteristic of [[triethyl borate|ethyl borate]] when ignited with concentrated H<sub>2</sub>SO<sub>4</sub> and ethanol.