In the field of chemistry, in general, bases (or hydroxides ) are called substances that, when dissolved in water, release hydroxyl ions (OH – ) and acids that are capable of releasing protons (H + ) .
The concept of bases and acids has been modified a little over time. It was Arrhenius who drew up the first definition, his theory had some limitations, since certain substances such as ammonia behave as bases without having the hydroxyl ion in its molecule. In addition, Arrhenius only considered the aqueous medium, but acid-base reactions also occur in other non-aqueous dissolution media .
Almost forty years later, around 1923, Brönsted and Lowry formulated another theory by stating that acids and bases act as conjugated pairs, so that acid is that substance capable of providing protons and the base is that capable of taking them . Even this theory was not completely complete, since there are several substances that have acidic properties without having ionizable hydrogen atoms in their molecule. That is why, as an additional part of his theory of interatomic covalent bonding , Lewis noted that acid is all that substance.
which can accept a pair of electrons to form a coordinate covalent bond (dative), while a substance is capable of yielding said electronic pair.
According to their tendency to dissociate into ions, acids and bases are classified as strong and weak . Acids lower the pH of the solutions , the bases or alkalis raise it. Strong acids are often corrosive, some substances dissolve better in media that have been slightly acidified or alkalized.
Some well known acids, by way of example:
- sulfuric acid ( H 2 SO 4 ) – is a strong acid with many uses, especially in heavy industry, very corrosive and irritating; when diluted, it releases a lot of heat, so it must be handled (like other strong acids) with great care. Intensely oxidizing
- hydrochloric acid ( HCl ) – although it is a strong acid, it is present in the human body, specifically in the stomach, where it plays an important role in the digestive process. Its excess generates heartburn.
- phosphoric acid ( H 3 PO 3 ) – this acid is a common ingredient in carbonated drinks. The usual consumption of such beverages is discouraged due to the negative impact of this acid on calcium metabolism, which affects bones and teeth especially.
- nitric acid ( HNO 3 ) – recognized strong acid, used to make explosives and nitrogen fertilizers, among other uses.
- Perchloric acid ( H ClO 4 ) – another strong acid that is liquid at room temperature, is one of the most oxidizing.
- Sulfhydric acid ( H 2 S ) – is a gaseous substance with a strong and unpleasant odor, toxic in high concentrations, has numerous industrial applications.
- Ribonucleic acid – is a central component of ribosomes, essential for the complete process of protein synthesis from deoxyribonucleic acid, closely related to it.
- acetylsalicylic acid – is a very important organic acid, with analgesic and anti-inflammatory properties; It is the basis of aspirin.
- lactic acid – comes from the degradation of glucose during anaerobic exercise of high intensity and short duration. In normal conditions that lactic acid is reused, but if it accumulates it causes damage to the muscle fibers, in the form of cramps especially.
- allylic acid – is an acid present in vegetables such as garlic or onion, derived from a precursor also present in such species, allicin. It is germicidal and antioxidant.
- Retinoic acid – applied topically, inhibits keratinization, is used in creams against acne and skin aging. It must be used under medical supervision.
- butyric acid – final product of the fermentation of certain carbohydrates conducted by rumen microorganisms; It is usually part of animal fats in small amounts.
- Propionic acid – food preservative, is used in order to prevent fungal and bacterial deterioration of bakery products and others.
- Benzoic acid – it is used as a preservative added to different products (mayonnaise, canned products), often in the form of salt (sodium benzoate)
- acetic acid – food preservative widely used in the home, based on vinaigrettes and marinades. It is the major component of vinegar.
- hydroiodic acid
- succinic acid
- hydrobromic acid
- citric acid
- oxalic acid
See also: Examples of Acids
Examples of bases
Now, some bases are listed (those of metals are generically known as hydroxides ):
- sodium hydroxide ( caustic soda )
- magnesium hydroxide ( milk of magnesia )
- calcium hydroxide (lime)
- potassium hydroxide
- barium hydroxide
- iron hydroxide
- zinc hydroxide
- copper hydroxide
- zirconium hydroxide
- titanium hydroxide
- aluminum hydroxide (antacid)