Qualitative tests can detect a particular ion, chemical or functional group.
To carry out qualitative reactions requires appropriate reagents, indicators, in some cases - the burner flame.
Qualitative reaction cations and anions
To determine the silver cation, you need to spendreaction with any chloride. Interaction Ag (+) and Cl (-) results in a white precipitate of AgCl ?. Barium Ba2 + cations are detected by reaction with sulfates: Ba (2 +) + SO4 (2 -) = BaSO4? (White precipitate). Equally true: to find a solution of chloride ions or sulfate ions, it is necessary to perform the reaction, respectively, with the silver and barium salts.
To determine cations Fe (2+) usinghexacyanoferrate (III) K3 Potassium [Fe (CN) 6], and more specifically, the complex ion [Fe (CN) 6] (3). The resulting dark blue precipitate Fe3 [Fe (CN) 6] 2 is called the "Turnbull's blue." To identify the cations of iron (III) hexacyanoferrate has taken (II) K4 potassium [Fe (CN) 6], which gives by reaction with Fe (3+) dark blue precipitate Fe4 [Fe (CN) 6] 3 - "Prussian Blue" . Detect Fe (3+) can also be reacted with ammonium thiocyanate NH4CNS. The result is a malodissotsiiruyuschy thiocyanate iron (III) - Fe (CNS) the third solution turned blood red.
Excess hydrogen cations H + creates an acidicenvironment in which the indicator color changes accordingly: orange methyl orange and purple litmus turns red. At the same excess of hydroxide ions OH- (alkaline medium) litmus paper turns blue, methyl orange - yellow and colorless in neutral and acidic environments phenolphthalein becomes crimson stain.
To understand whether there is a solution of ammonium cationNH4 +, you need to add alkali. A reversible interaction with hydroxide ions NH4 + gives ammonia NH3? and water. Ammonia has a characteristic odor and wet litmus paper turns blue in such a solution.
In response to the high-quality ammonia reagent used HCl. During the formation of ammonia and hydrogen chloride from ammonium chloride HN4Cl white smoke can be seen.
The carbonate and bicarbonate ions CO3 (2-) and HCO3 (-)It can be detected by adding acid. The interaction of these ions with hydrogen cations produces carbon dioxide and water is formed. By passing the resulting gas through lime water Ca (OH) 2 solution was cloudy, since the formed insoluble compound - calcium carbonate, CaCO3 ?. With further passage of carbon dioxide formed acid salt - soluble calcium bicarbonate already Ca (HCO3) 2.
Reagent for the detection of sulfide ions S (2-) - soluble lead salt, giving a reaction with S (2-) black precipitate PbS ?.
Detection of the ions by a burner
The salts of certain metals when making the flameBurner stain it. This property is used in a qualitative assay for the detection of cations of these elements. Thus, Ca (2+) in the flame stains brick red color, Ba (2+) - yellow-green. potassium salts Burning is accompanied by the violet flame, lithium - bright red, sodium - yellow, strontium - carmine red.
Qualitative reactions in organic chemistry
Compounds with double and triple bonds (alkenesalkadienes, alkynes) decolorized red-brown bromine water and Br2 pink solution of potassium permanganate, KMnO4. Substances with two or more gidroksogrupp -OH (polyhydric alcohols, monosaccharides, disaccharides) was dissolved in a freshly prepared alkaline medium blue precipitate Cu (OH) 2 to form a bright blue colored solution. With hydroxide Copper (II) react as aldehydes and reducing disaccharide aldose (aldehyde group), but falls here already precipitate Cu2O? brick-red color.
Phenol solution of ferric chloride (III) formscomplexed with FeCl3 gives violet staining. Compounds containing an aldehyde group, the reaction yield of "silver mirror" with an ammoniacal solution of silver oxide. A solution of iodine when incorporated in it becomes violet starch, and peptide bonds of proteins found in the reaction with a saturated copper sulfate solution and concentrated sodium hydroxide solution.