Lye

Alkaline solutions or colloquially bases are aqueous solutions of metal hydroxides such as sodium hydroxide ( caustic soda) or potassium hydroxide ( caustic potash ). These metal hydroxides are among the alkali metal hydroxides. In a broader sense we use the term for any solution of bases. These include ammonia (ammonia water) and organic compounds such as amines. Alkaline solutions in the broadest sense may also be non-aqueous solutions.

Aqueous solutions are alkaline, when the concentration of hydroxide ion OH - to the oxonium ion H3O excess. The pH is greater than 7 then strongly alkaline aqueous solutions having a pH greater than 10, for example, has a normal sodium hydroxide solution, a pH of 14

Properties

Acids and alkaline solutions have some common characteristics. These solutions arise with indicators characteristic colorations and feel slippery on the skin. The solutions are corrosive, so must when working with alkaline solutions always wear safety glasses. They also show electrical conductivity, so it must be freely movable ions.

Strong alkaline solutions are extremely corrosive: You can metals, such as aluminum, and proteins dissolve, so skin contact should be avoided with them. When dealing with highly alkaline solutions should therefore gloves and safety goggles. You can - especially with long exposure in the heat - also attack glass surfaces. This can lead for example to a turbidity of glasses. The handling of caustic soda etc. in glass vessels such as Erlenmeyer flask is of course still possible as long as no ground-glass stoppers from glass are used, since they settle on prolonged storage.

Use

Alkaline solutions are used, among other things, to cure and preserve food so as to thereby make them more durable. Furthermore liquors are also used in baking pretzels or pretzel roll. In the chemical production of liquors can also be used to neutralize acids.

Production of alkaline solutions

Preparation of aqueous alkali metal hydroxide solutions

The following reactions, each led by example, lead to the formation of aqueous solutions of alkali metal hydroxides:

Solve the corresponding hydroxide in water

This is the simplest way for the practical use of the solutions in the laboratory. However, the heat development while solving (exothermic reaction) can be so strong that the water begins to boil, sprinkle with the alkaline solution and can cause burns. example:

Reaction of an alkali metal with water

It forms upon addition of a stoichiometric amount of water -resistant material suitable alkali metal hydroxide, with the addition of water in excess of one alkali metal hydroxide solution. The dissolution process described in Production Variant 1 takes place with the formed in the reaction of lithium hydroxide. example:

Reacting an alkali metal with water

As with the second production variant also the added material amount of water is crucial for the creation or designation of the product. example:

On addition of water in excess of the dissolution process of the sodium hydroxide from production variant occurs first, depending on the alkali metal used and the experimental procedure, the resulting hydrogen ignited by the released heat of reaction.

An important variant is the industrial production of sodium hydroxide by the reaction of water with sodium amalgam, which is obtained from the chlor-alkali electrolysis with mercury electrodes.

Electrolysis of alkali metal halide salt solutions

By the electrolysis of sodium chloride solution on a large scale caustic soda is produced, one by a porous barrier ( diaphragm) largely prevents the brine and caustic soda mix. Thus, a continuous electrolysis is possible:

Lye