Acid hydroxides are inorganic compounds of the hydroxyl group –OH and metal or non-metal with an oxidation state of +5, +6. Another name is oxygen-containing inorganic acids. Their feature is the proton cleavage during dissociation.
Hydroxide Classification
Hydroxides are also called hydroxides and hydroxides. Almost all chemical elements have them, some are widespread in nature, for example, the minerals hydrargillite and brucite are aluminum and magnesium hydroxides, respectively.
The following types of hydroxides are distinguished:
The classification is based on the belonging of the oxide forming the hydroxide to the basic, acid or amphoteric type.
General properties
Of greatest interest are the acid-base properties of oxides and hydroxides, since the possibility of reactions proceeding depends on them. Whether the hydroxide exhibits acidic, basic, or amphoteric properties depends on the strength of the bond between oxygen, hydrogen, and the element.
Strength is affected by the ionic potential, with an increase in which the basic ones weaken and the acidic properties of hydroxides are enhanced.
Higher hydroxides
Higher hydroxides are compounds in which the forming element is in the highest oxidation state. Such are among all types in the class. An example of a base is magnesium hydroxide. Aluminum hydroxide is amphoteric, and perchloric acid can be classified as acid hydroxide.
The change in the characteristics of these substances depending on the forming element can be traced by the periodic system of D. I. Mendeleev. The acidic properties of higher hydroxides are enhanced from left to right, and metal, respectively, weaken in this direction.
Basic hydroxides
In a narrow sense, this type is called the base, since OH anion is cleaved during its dissociation. The most famous of these compounds are alkalis, for example:
- Hydrated lime Ca (OH) 2 , used for whitewashing rooms, tanning leathers, for preparing antifungal fluids, mortars and concrete, softening water, producing sugar, bleach and fertilizers, causticizing sodium and potassium carbonates, neutralizing acidic solutions, detecting carbon dioxide , disinfection, reduction of soil resistivity, as a food additive.
- KOH caustic potash used in photography, oil refining, food, paper and metallurgy, as well as an alkaline battery, acid neutralizer, catalyst, gas scrubber, hydrogen indicator, electrolyte, component of detergents, drilling fluids, dyes, fertilizers, potassium organic and inorganic substances, pesticides, pharmaceuticals for the treatment of warts, soaps, synthetic rubber.
- NaOH caustic soda , necessary for the pulp and paper industry, saponification of fats in the production of detergents, neutralizing acids, making biodiesel, dissolving blockages, degassing toxic substances, treating cotton and wool, washing molds, food production, cosmetology, photography.
Basic hydroxides are formed as a result of interaction with water of the corresponding metal oxides, in the vast majority of cases with an oxidation state of +1 or +2. These include alkaline, alkaline earth and transition elements.
In addition, the bases can be obtained in the following ways:
- the interaction of alkali with a salt of inactive metal;
- a reaction between an alkaline or alkaline earth element and water;
- electrolysis of an aqueous solution of salt.
Acidic and basic hydroxides interact with each other with the formation of salt and water. Such a reaction is called neutralization and is of great importance for titrimetric analysis. In addition, it is used in everyday life. When spilling acid, a hazardous reagent can be neutralized with soda, and vinegar is used for alkali.
In addition, basic hydroxides shift the ionic equilibrium during dissociation in solution, which manifests itself in a change in the colors of the indicators, and enter into metabolic reactions.
When heated, insoluble compounds decompose into oxide and water, and alkalis melt. Basic hydroxide and acid oxide form a salt.
Amphoteric hydroxides
Some elements, depending on conditions, exhibit either basic or acidic properties. Hydroxides based on them are called amphoteric. They can easily be determined by the constituent metal having an oxidation state of +3, +4. For example, a white gelatinous substance - aluminum hydroxide Al (OH) 3 , used in water treatment due to its high adsorption ability, the manufacture of vaccines as a substance that enhances the immune response in medicine for the treatment of acid-dependent diseases of the gastrointestinal tract. It is also often included in the composition of plastics to suppress combustion and acts as a carrier for catalysts.
But there are exceptions when the value of the oxidation state of the element is +2. This is characteristic of beryllium, tin, lead and zinc. The hydroxide of the latter metal Zn (OH) 2 is widely used in chemical industries, primarily for the synthesis of various compounds.
Amphoteric hydroxide can be obtained by conducting a reaction between a solution of a salt of a transition metal and dilute alkali.
Amphoteric hydroxide and acid oxide, alkali or acid form a salt upon reaction. Heating of the hydroxide leads to its decomposition into water and metahydroxide, which, when heated further, is converted to oxide.
Amphoteric and acidic hydroxides behave identically in an alkaline environment. When interacting with acids, amphoteric hydroxides act as bases.
Acid hydroxides
This type is characterized by the presence in the composition of the element in the oxidation state from +4 to +7. In solution, they are able to give off a hydrogen cation or take an electron pair and form a covalent bond. Most often, they have the state of aggregation of the liquid, but there are also solid substances among them.
Forms a hydroxide acid oxide, capable of salt formation and containing non-metal or transition metal. The oxide is obtained as a result of the oxidation of non-metal, the decomposition of an acid or salt.
The acidic properties of hydroxides are manifested in their ability to color indicators, dissolve active metals with the release of hydrogen, react with bases and basic oxides. Their distinctive feature is participation in redox reactions. During the chemical process, they attach to themselves negatively charged elementary particles. The ability to act as an electron acceptor weakens when diluted and converted into salts.
Thus, it is possible to distinguish not only the acid-base properties of hydroxides, but also oxidative ones.
Nitric acid
HNO 3 is considered a strong monobasic acid. She is very poisonous, leaves ulcers on the skin with yellow staining of the integument, and her fumes instantly irritate the mucous membrane of the respiratory tract. The outdated name is strong vodka. It refers to acid hydroxides; in aqueous solutions it completely dissociates into ions. Outwardly, it looks like a colorless, smoking liquid in the air. Concentrated is an aqueous solution, which includes 60 - 70% of the substance, and if the content exceeds 95%, it is called fuming nitric acid.
The higher the concentration, the darker the liquid looks. It may even have a brown color due to decomposition into oxide, oxygen and water in the light or with little heat, so it should be stored in a dark glass container in a cool place.
The chemical properties of acid hydroxide are such that it can be distilled without decomposition only under reduced pressure. All metals except gold, some representatives of the platinum group and tantalum react with it, but the final product depends on the concentration of acid.
For example, a 60% substance, when reacted with zinc, gives nitrogen dioxide as the predominant by-product, 30% gives monoxide, 20% gives diazot oxide (laughing gas). Even lower concentrations of 10% and 3% give the simple substance nitrogen in the form of gas and ammonium nitrate, respectively. Thus, based on the acid, various nitro compounds can be obtained. As can be seen from the example, the lower the concentration, the deeper the restoration of nitrogen. It also affects the activity of the metal.
A substance can dissolve gold or platinum only as a part of aqua regia - a mixture of three parts of hydrochloric and one nitric acid. Glass and polytetrafluoroethylene are resistant to it.
In addition to metals, the substance reacts with basic and amphoteric oxides, bases, weak acids. In all cases, the result is salts; with non-metals, acids. Not all reactions occur safely; for example, amines and turpentine self-ignite upon contact with the hydroxide in a concentrated state.
Salts are called nitrates. When heated, they decompose or exhibit oxidizing properties. In practice, they are used as fertilizers. Almost never occur in nature due to high solubility, therefore, all salts except potassium and sodium are obtained artificially.
The acid itself is obtained from synthesized ammonia and, if necessary, concentrated in several ways:
- a shift in equilibrium by increasing pressure;
- heating in the presence of sulfuric acid;
- by distillation.
Further, it is used in the production of mineral fertilizers, dyes and medicines, the military industry, easel graphics, jewelry, organic synthesis. Occasionally, dilute acid is used in photography to acidify tinted solutions.
Sulfuric acid
H 2 SO 4 is a strong dibasic acid. It looks like a colorless heavy oily liquid, has no smell. The outdated name is vitriol (aqueous solution) or vitriol oil (a mixture with sulfur dioxide). This name was given due to the fact that at the beginning of the XIX century sulfur was produced in vitriol plants. In tribute to tradition, sulfate crystalline hydrates are still called vitriol.
Acid production has been established on an industrial scale and amounts to about 200 million tons per year. It is obtained by oxidizing sulfur dioxide with oxygen or nitrogen dioxide in the presence of water or by the interaction of hydrogen sulfide with sulfate of copper, silver, lead or mercury. The resulting concentrated substance is a strong oxidizing agent: it displaces halogens from the corresponding acids, converts carbon and sulfur to acid oxides. In this case, hydroxide is reduced to sulfur dioxide, hydrogen sulfide or sulfur. Diluted acid usually does not exhibit oxidizing properties and forms medium and acid salts or esters.
The substance can be detected and identified by reaction with soluble barium salts, resulting in a white sulfate precipitate.
In the future, acid is used in the processing of ores, the production of mineral fertilizers, chemical fibers, dyes, smoke and explosives, various industries, organic synthesis, as an electrolyte, to obtain mineral salts.
But the application is fraught with certain dangers. The corrosive substance causes chemical burns in contact with skin or mucous membranes. When inhaled, a cough first appears, and subsequently inflammatory diseases of the larynx, trachea, and bronchi. Exceeding the maximum permissible concentration of 1 mg per cubic meter is deadly.
You can encounter sulfuric acid vapors not only in specialized industries, but also in the atmosphere of the city. This happens when chemical and metallurgical enterprises emit sulfur oxides, which then fall in the form of acid rain.
All these dangers have led to the fact that the circulation of sulfuric acid containing more than 45% of the mass concentration in Russia is limited.
Sulphurous acid
H 2 SO 3 is a weaker acid compared to sulfuric. Its formula differs by only one oxygen atom, but this makes it unstable. In the free state, it is not isolated; it exists only in dilute aqueous solutions. They can be identified by a specific pungent odor reminiscent of a burnt match. And to confirm the presence of sulfite-ion - by reaction with potassium permanganate, as a result of which the red-violet solution becomes discolored.
The substance in various conditions can act as a reducing agent and an oxidizing agent, form acidic and medium salts. It is used for food preservation, the production of cellulose from wood, as well as for the delicate whitening of wool, silk and other materials.
Orthophosphoric acid
H 3 PO 4 is an acid of medium strength that looks like colorless crystals. Also, phosphoric acid is an 85% solution of these crystals in water. It looks like odorless syrupy liquid, prone to hypothermia. Heating above 210 degrees Celsius leads to its conversion to pyrophosphoric acid.
Phosphoric acid is well soluble in water, neutralized by alkalis and ammonia hydrate, reacts with metals, forms polymer compounds.
You can get a substance in different ways:
- dissolving red phosphorus in water under pressure, at a temperature of 700-900 degrees, using platinum, copper, titanium or zirconium;
- boiling red phosphorus in concentrated nitric acid;
- adding hot concentrated nitric acid to phosphine;
- oxidation of phosphine oxygen at 150 degrees;
- exposing the tetrafosphorus to decaoskide at a temperature of 0 degrees, then gradually increasing it to 20 degrees and gradually transition to boiling (water is needed at all stages);
- dissolving pentachloride or phosphorus trichloride in water.
The use of the resulting product is wide. With its help, surface tension is reduced and oxides are removed from surfaces preparing for soldering, metals are cleaned of rust and a protective film is created on their surface that prevents further corrosion. In addition, phosphoric acid is used in industrial freezers and for research in molecular biology.
The compound is also part of aviation hydrofluids, food additives and acidity regulators. It is used in fur farming for the prevention of urolithiasis in minks and in dentistry for manipulations prior to filling.
Pyrophosphoric acid
H 4 P 2 O 7 is an acid characterized as strong in the first step and weak in the rest. It melts without decomposition, since this process requires heating in a vacuum or the presence of strong acids. It is neutralized by alkalis and reacts with hydrogen peroxide. Get it in one of the following ways:
- the decomposition of tetraphosphorus decoxide in water at zero temperature, and then heating it to 20 degrees;
- heating phosphoric acid to 150 degrees;
- the interaction of concentrated phosphoric acid with tetraphosphorus decoxide at 80-100 degrees.
The product is mainly used for the production of fertilizers.
In addition to these, there are many other representatives of acid hydroxides. Each of them has its own characteristics and characteristics, but in general, the acidic properties of oxides and hydroxides are their ability to split off hydrogen, decompose, interact with alkalis, salts and metals.