Halide

Halides are chemical connections between elements of the seventh main group ( more specifically, the 17 group) of the Periodic Table, halogens as above, and members of other groups. In addition, the singly negatively charged ions of the halogens (F, Cl, Br, I, At ) as the halide ions ( briefly also halides ) refers.

Wherein the compounds are different (depending on the type of chemical bond):

• Salt -like halides, ionic compounds (salts ) made due to the large electronegativity difference between the elements involved in anions and cations and are held together by electrostatic interactions. Examples include sodium chloride (NaCl) and potassium bromide (KBr).

• Covalent halides, covalent compounds in which the electronegativity difference is not as great as in the above mentioned ionic compounds, the compounds, however, have a charge polarity. Examples are hydrogen halides such as hydrogen chloride (HCl) and inter-halogen compounds. And halogenated hydrocarbons such as methylene chloride (dichloromethane, CH2Cl2), and other organic compounds containing halogens, are often referred to as the halides, but does not correspond to the most recent nomenclature.

• Complex halides with halide ions as complexing ligands, such as the tetrachloroplatinate ion [ PtCl 4 ] 2 -.

Oxidation of halides

The halides can be oxidized graded according to the electrochemical series for elementary halogen.

Problem

Halides and halogen-containing compounds are found in the chemical industry often. Thus, for example, chloroform and dichloromethane good organic solvent. Due to its low boiling point, however, also shares get them into the environment and atmosphere. Under the action of sunlight on halides then halogen radicals are formed, which in turn affect the ozone layer (see: ozone hole ).

The aim is therefore to consider the use of halogenated solvents as low as possible. Therefore, CFC-containing substances for spray cans and refrigerators in the 80s and 90s of the 20th century were banned.

Many classified as toxic or hazardous to the environment salt-like halides are attached in some countries in small amounts foods, salt, dental care products or drinking water. These resources include sodium fluoride and sodium iodide.

Detection reactions

Detection with silver nitrate and ammonia

Chloride, bromide and iodide can be precipitated with silver nitrate in a test reaction from aqueous solution after acidification with nitric acid.

For example, in a saline solution:

The Silberhalogenidniederschlag is then further investigated with ammonia water:

• Silver (I ) fluoride ( AgF ) is readily soluble in water as the only silver.
• Silver chloride ( AgCl) forms a white, curdy precipitate, which dissolves again on addition of ammonia to form the colorless Diamminsilber ( I) in a complex formation reaction:

• Silver bromide ( AgBr ) precipitates as a pale yellow, soluble only in concentrated ammonia precipitation.
• Silver iodide ( AgI ) appears as a greenish yellow precipitate which does not dissolve in concentrated ammonia.

All silver halides decompose on exposure to light and dissolve in concentrated sodium thiosulphate ( hypo ).

Proof as elemental bromine and iodine

A further possibility of distinguishing bromine and iodine, the addition of hydrogen chloride, or chloramine T with hydrochloric acid wherein bromide and iodide can be oxidized to halogen by chlorine.

By extraction in an organic solvent, the dyes are particularly well visible. In an oxygen- free solvents such as dichloromethane or n-hexane iodine pink violet, in oxygen-containing solvents such as diethyl ether brown. Bromine colors the solution brown. The subsequent reaction to bromine chloride colored wine yellow solution.

Titration

For quantitative detection of halide ions three titration methods are used, which are also based on the solubility of the silver halides:

• Titration according to Mohr
• Titration according to Volhard
• Titration according to Fajans