Alkaline is a term used in biochemistry and chemistry. Alkaline means basic. If a solution has a pH value of more than 7, it is described as alkaline.

Alkalis are substances that form alkaline solutions (lyes) with water. For this reason, they were previously also referred to as alkali salts. This group of substances, which is not clearly defined, includes in particular the oxides and hydroxides of alkali metals and alkaline earth metals and, to a lesser extent, other metals. Alkalis belong to the group of bases. In 1755, Joseph Black distinguished between the initially unspecific definition of alkalis as oxides or hydroxides on the one hand and carbonates on the other. Today, it is mainly the hydroxides of alkali metals, in particular sodium and potassium hydroxide, that are colloquially referred to as alkalis.

When you add an alkali to a fat, you actually split off the esters of the carboxylic acids. The result is glycerine and the alkali salts of the fatty acids, which are soaps.

The phosphoric acid esters of RNA (but not of DNA) are also cleaved by alkalis, releasing the mononucleotide building blocks from the RNA in the form of ribonucleoside-3′-phosphates and ribonucleoside-2′-phosphates.

Proteins and DNA are denatured by alkalis, but the unfolded peptide chains or DNA single strands remain intact. They dissociate into the corresponding metal ions and hydroxide ions in aqueous solution.

Hydroxide alkalis were previously also referred to as caustic or corrosive alkalis. The hydroxide ions in the solutions cause an alkaline reaction from a concentration of 10-7 M. Concentrations between 10-7 and 10-3 M (pH values between 7 and 11) are referred to as weak alkalis, concentrations of 10-3 to 1 M (pH values between 11 and 14) as strong alkalis.

Alkalis are characterized by

• their solubility in water
• their corrosive aqueous solutions, i.e. their destructive effect on plant and animal substances
• their peculiar pungent tasteref name="Henry Enfield Roscoe" />
• their ability to absorb carbon dioxide from the air, e.g. soda lime
• their ability to combine with acids to form salts
• their ability to form soaps and glycerine with fats and fatty oils: Saponification
• Alkalis dye reddened, moist litmus paper bluish and yellow turmeric dye brown

Alkalis form hydroxide ions (OH-) in solutions.

Alkalis are a type of chemical which, when dissolved in water, break down the esters of carboxylic acids. For this reason, the alkali treatment of fats leads to the formation of glycerine and the alkali salts of fatty acids, the soaps.

The phosphoric acid esters of RNA (but not of DNA) are also cleaved by alkalis, releasing the mononucleotide building blocks from the RNA in the form of ribonucleoside-3′-phosphates and ribonucleoside-2′-phosphates. Proteins and DNA are denatured by alkalis (denaturation), but the unfolded peptide chains or DNA single strands remain intact. They dissociate into the corresponding metal ions and hydroxide ions in aqueous solution.

Alkaline solutions - also known as alkalis - are aqueous solutions in which the concentration of hydroxide ions OH- exceeds that of oxonium ions H3O+, so that the pH value of the solution is greater than 7. In order to make the statements somewhat more precise, graded designations such as weak or very weak alkaline or strongly alkaline are also commonly used, whereby strongly alkaline aqueous solutions generally have a pH value of over 10. For example, a sodium hydroxide solution containing 4 g of sodium hydroxide (NaOH) in 100 ml of water has the highest possible pH value of 14. Such strongly alkaline solutions, which are then also referred to as strong alkalis, can severely damage the skin surface of humans and animals even after brief exposure. However, these strongly alkaline solutions can only be produced from the metal oxides of alkali and alkaline earth metals, which are more or less soluble in water and are therefore also referred to as basic oxides. When these oxides react with water, they form the corresponding metal hydroxides of the alkali and alkaline earth metals.