Acid hydroxides are inorganic compounds of the hydroxyl group –OH and a metal or non-metal with an oxidation state of +5, +6. Another name is oxygen-containing inorganic acids. Their feature is the elimination of a proton during dissociation.
Classification of hydroxides
Hydroxides are also called hydroxides and vodoxides. Almost all chemical elements have them, some are widely distributed in nature, for example, the minerals hydrargillite and brucite are aluminum and magnesium hydroxides, respectively.
The following types of hydroxides are distinguished:
- basic;
- amphoteric;
- acid.
Classification is based on whether the oxide forming the hydroxide is basic, acidic, or amphoteric.
General Properties
The most interesting are the acid-base properties of oxides and hydroxides, since the possibility of reactions depends on them. Whether the hydroxide will be acidic, basic, or amphoteric depends on the strength of the bond between oxygen, hydrogen, and the element.
Ion strength is affectedpotential, with an increase in which the basic properties of hydroxides weaken and the acidic properties of hydroxides increase.
Higher hydroxides
Higher hydroxides are compounds in which the forming element is in the highest oxidation state. These are among all types in the class. An example of a base is magnesium hydroxide. Aluminum hydroxide is amphoteric, while perchloric acid can be classified as an acidic hydroxide.
Change in the characteristics of these substances depending on the forming element can be traced according to the periodic system of D. I. Mendeleev. The acidic properties of higher hydroxides increase from left to right, while the metallic properties, respectively, weaken in this direction.
Basic hydroxides
In a narrow sense, this type is called a base, since the OH anion is split off during its dissociation. The most famous of these compounds are alkalis, for example:
- Slaked lime Ca(OH)2 used for whitewashing rooms, tanning leather, preparing antifungal liquids, mortars and concrete, softening water, producing sugar, bleach and fertilizer, causticization of sodium and potassium carbonates, neutralization of acidic solutions, detection of carbon dioxide, disinfection, reduction of soil resistivity, as a food additive.
- KOH caustic potash used in photography, oil refining, food, paper and metallurgical industries, as well as an alkaline battery, acid neutralizer, catalyst, gas purifier, pH regulator, electrolyte,component of detergents, drilling fluids, dyes, fertilizers, potash organic and inorganic substances, pesticides, pharmaceutical preparations for the treatment of warts, soaps, synthetic rubber.
- Caustic soda NaOH, required for pulp and paper industry, saponification of fats in the production of detergents, acid neutralization, biodiesel production, blockage dissolving, degassing of toxic substances, cotton and wool processing, mold washing, 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, bases can be obtained in the following ways:
- interaction of alkali with a s alt of a low-active metal;
- reaction between an alkaline or alkaline earth element and water;
- by electrolysis of an aqueous solution of s alt.
Acidic and basic hydroxides interact with each other to form s alt and water. This reaction is called neutralization and is of great importance for titrimetric analysis. In addition, it is used in everyday life. When acid is spilled, a dangerous reagent can be neutralized with soda, and vinegar is used for alkali.
In addition, basic hydroxides shift the ionic equilibrium when dissociated in solution, which is manifested in a change in the colors of the indicators, and enter into exchange reactions.
When heated, insoluble compounds decompose into oxide and water, and alkalis melt. A basic hydroxide and an acidic oxide form a s alt.
Amphoteric hydroxides
Some elements, depending on the conditions, exhibit either basic or acidic properties. Hydroxides based on them are called amphoteric. They are easy to identify by the metal included in the composition, which has an oxidation state of +3, +4. For example, a white gelatinous substance - aluminum hydroxide Al(OH)3, used in water purification due to its high adsorbing capacity, in the manufacture of vaccines as a substance that enhances the immune response, in medicine for the treatment of acid-dependent diseases gastrointestinal tract. It is also often incorporated into flame retardant plastics 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 typical for beryllium, tin, lead and zinc. Hydroxide of the last metal Zn(OH)2 is widely used in chemical industries, primarily for the synthesis of various compounds.
You can get amphoteric hydroxide by reacting a solution of a transition metal s alt with dilute alkali.
Amphoteric hydroxide and acid oxide, alkali or acid form a s alt when interacting. Heating hydroxide leads to its decomposition into water and metahydroxide, which, upon further heating, is converted into oxide.
Amphoteric andacidic hydroxides behave in the same way in an alkaline environment. When interacting with acids, amphoteric hydroxides act as bases.
Acid hydroxides
This type is characterized by the presence of an element in the oxidation state from +4 to +7. In solution, they are able to donate a hydrogen cation or accept an electron pair and form a covalent bond. Most often they have a state of aggregation of a liquid, but there are also solids among them.
Forms a hydroxide acidic oxide capable of s alt formation and containing a non-metal or transition metal in its composition. The oxide is obtained as a result of the oxidation of a non-metal, the decomposition of an acid or a s alt.
The acidic properties of hydroxides are manifested in their ability to color indicators, dissolve active metals with hydrogen evolution, react with bases and basic oxides. Their distinctive feature is participation in redox reactions. During the chemical process, they attach negatively charged elementary particles to themselves. The ability to act as an electron acceptor is weakened by dilution and conversion to s alts.
Thus, it is possible to distinguish not only the acid-base properties of hydroxides, but also the oxidizing ones.
Nitric acid
HNO3 is considered a strong monobasic acid. It is very poisonous, leaves ulcers on the skin with yellow staining of the integument, and its vapors instantly irritate the respiratory mucosa. The old name is strong vodka. It refers to acid hydroxides, in aqueous solutionscompletely dissociates into ions. Outwardly, it looks like a colorless liquid fuming in air. A concentrated aqueous solution is considered to be 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 appears. It may even have a brown color due to decomposition into oxide, oxygen and water in the light or with slight heating, 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 only be distilled without decomposition under reduced pressure. All metals react with it except gold, some representatives of the platinum group and tantalum, but the final product depends on the concentration of the acid.
For example, a 60% substance, when interacting with zinc, gives nitrogen dioxide as the predominant by-product, 30% - monoxide, 20% - dinitrogen oxide (laughing gas). Even lower concentrations of 10% and 3% give a simple substance nitrogen in the form of gas and ammonium nitrate, respectively. Thus, various nitro compounds can be obtained from the acid. As can be seen from the example, the lower the concentration, the deeper the reduction of nitrogen. The activity of the metal also affects this.
A substance can dissolve gold or platinum only in the composition of aqua regia - a mixture of three parts of hydrochloric and one nitric acid. Glass and PTFE are resistant to it.
In addition to metals, the substance reacts withbasic and amphoteric oxides, bases, weak acids. In all cases, the result is s alts, with non-metals - acids. Not all reactions occur safely, for example, amines and turpentine spontaneously ignite when in contact with hydroxide in a concentrated state.
S alts are called nitrates. When heated, they decompose or exhibit oxidizing properties. In practice, they are used as fertilizers. They practically do not occur in nature due to high solubility, therefore, all s alts except potassium and sodium are obtained artificially.
The acid itself is obtained from synthesized ammonia and, if necessary, concentrated in several ways:
- shifting balance by increasing pressure;
- by heating in the presence of sulfuric acid;
- distillation.
Then 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 tinting solutions.
Sulfuric acid
Н2SO4 is a strong dibasic acid. It looks like a colorless heavy oily liquid, odorless. The obsolete 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 19th century sulfur was produced at vitriol plants. In tribute to tradition, sulfate hydrates are still called vitriol to this day.
The production of acid is established on an industrial scale andis 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 reacting hydrogen sulfide with copper, silver, lead or mercury sulfate. The resulting concentrated substance is a strong oxidizing agent: it displaces halogens from the corresponding acids, converts carbon and sulfur into acid oxides. The hydroxide is then reduced to sulfur dioxide, hydrogen sulfide or sulfur. A dilute acid usually does not show oxidizing properties and forms medium and acidic s alts or esters.
The substance can be detected and identified by reaction with soluble barium s alts, as a result of which a white precipitate of sulfate precipitates.
The acid is further 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 s alts.
But the use is fraught with certain dangers. Corrosive substance causes chemical burns on 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 allowable concentration of 1 mg per cubic meter is deadly.
You can encounter sulfuric acid fumes not only in specialized industries, but also in the atmosphere of the city. This happens when chemical and metallurgicalenterprises emit sulfur oxides, which then fall as acid rain.
All these dangers have led to the fact that the circulation of sulfuric acid containing more than 45% mass concentration in Russia is limited.
Sulfurous acid
Н2SO3 - weaker acid than sulfuric acid. Its formula differs by only one oxygen atom, but this makes it unstable. It has not been isolated in the free state; it exists only in dilute aqueous solutions. They can be identified by a specific pungent smell, reminiscent of a burnt match. And to confirm the presence of a sulfite ion - by reaction with potassium permanganate, as a result of which the red-violet solution becomes colorless.
A substance under different conditions can act as a reducing agent and an oxidizing agent, form acidic and medium s alts. It is used for food preservation, obtaining cellulose from wood, as well as for delicate bleaching of wool, silk and other materials.
Orthophosphoric acid
H3PO4 is a medium strength acid that looks like colorless crystals. Orthophosphoric acid is also called an 85% solution of these crystals in water. It appears as an odorless, syrupy liquid that is prone to hypothermia. Heating above 210 degrees Celsius causes it to turn into pyrophosphoric acid.
Phosphoric acid dissolves well in water, neutralizes with alkalis and ammonia hydrate, reacts with metals,forms polymer compounds.
You can get the 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;
- by adding hot concentrated nitric acid to phosphine;
- oxidation of phosphine oxygen at 150 degrees;
- exposing tetraphosphorus decaooxide to a temperature of 0 degrees, then gradually increasing it to 20 degrees and a smooth transition to boiling (water is needed at all stages);
- dissolving pentachloride or phosphorus trichloride oxide in water.
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 included in aviation hydraulic fluids, 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
H4R2O7 - an acid characterized as strong in the first stage and weak in others. She melts withoutdecomposition, 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:
- decomposing tetraphosphorus decaoxide in water at zero temperature and then heating it to 20 degrees;
- by heating phosphoric acid to 150 degrees;
- reaction of concentrated phosphoric acid with tetraphosphorus decaoxide at 80-100 degrees.
Used mainly for fertilizer production.
Besides these, there are many other representatives of acidic hydroxides. Each of them has its own characteristics and characteristics, but in general, the acidic properties of oxides and hydroxides lie in their ability to split off hydrogen, decompose, interact with alkalis, s alts and metals.
