Physical properties of acetic acid, formula

The usual bottle of food vinegar, which can be found in the kitchen of any housewife, has many other acids and vitamins. Adding a couple of drops of the product to cooked food, salads causes a natural enhancement of taste. But very few of us seriously thought about the properties and real scales of application of the main component - acetic acid.

What is this substance?

The formula of acetic acid CH ₃ COOH, which relates it to a number of fatty carboxylic acids. The presence of one carboxyl group (COOH) refers to monobasic acids. The substance is found on the globe in organic form and is obtained synthetically in laboratories. Acid is the simplest, but no less important representative of its series. Easily soluble in water, hygroscopic.

The physical properties of acetic acid and density vary depending on the temperature regime. At room temperature, at 20 ° C, the acid is in the liquid state and has a density of 1.05 g / cm ³ . Has a specific smell and sour taste. The solution of the substance without impurities hardens and passes into crystals at a temperature below 17 ° C. The process of boiling acetic acid begins at a temperature above 117 ° C. The methyl group (CH ₃ ) of the acetic acid formula is obtained by the interaction of alcohols with oxygen: fermentation of alcohol substances and carbohydrates, Souring of wine.

A bit of history

The discovery of vinegar was one of the first in a series of acids and was carried out in stages. At first, acetic acid began to be extracted by distillation of Arab scientists of the 8th century. However, even in ancient Rome, this substance, derived from sour wine, was used as a universal sauce. The name itself from Ancient Greek is translated as "sour". In the 17th century, scientists in Europe managed to extract a pure substance of matter. At that time, they withdrew the formula and found an unusual ability - acetic acid in the vapor state was ignited by blue fire.

Until the 19th century, scientists found the presence of acetic acid only in organic form - as part of the compounds of salts and ethers. In the composition of plants and their fruits: apples, grapes. In the body of humans and animals: sweat secretions, bile. At the beginning of the 20th century, Russian scientists accidentally extracted acetic aldehyde from the reaction of acetylene with mercury oxide. For today, the consumption of acetic acid is so great that its main production only occurs in a synthetic way on a huge scale.

Methods of extraction

Will there be pure acetic acid or with the presence of impurities in the solution Depends on the method of extraction. Food acetic acid is obtained by a biochemical method in the process of ethanol fermentation. In industry, several ways of extracting acid are isolated. As a rule, reactions are accompanied by a high temperature and the presence of catalysts:

• Methanol in reaction with carbon (carbonylation).
• Oxidation of the oil fraction with oxygen.
• Pyrolysis of wood.
• Oxidation of acetaldehyde with oxygen.

The industrial method is more efficient and economical than biochemical. Thanks to the industrial method, the volume of production of acetic acid in the 20-th and 21-st century has grown hundreds of times, compared with the 19th century. Today, the synthesis of acetic acid by carbonylation of methanol gives more than 50% of the total volume produced.

The physical properties of acetic acid and its effect on the indicator

In liquid state, acetic acid is colorless. The acidity level of pH 2,4 is easily checked with a litmus test. Acetic acid when it hits the indicator stains it red. The physical properties of acetic acid vary visually. When the temperature drops below 16 ° C, the substance takes a solid form and resembles small ice crystals. It dissolves easily in water and interacts with a wide range of solvents, except hydrogen sulfide. Acetic acid reduces the total volume of the liquid when diluted with water. Independently describe the physical properties of acetic acid, its color and consistency, which you observe in the following image.

The substance ignites at a temperature of 455 ° C with a heat release of 876 kJ / mol. The molar mass is 60.05 g / mol. The physical properties of acetic acid as an electrolyte in reactions are weak. The permittivity is 6.15 at room temperature. Pressure, like density, is a variable physical property of acetic acid. At a pressure of 40 mm. Gt; Art. And a temperature of 42 ° C., the boiling process will begin. But already at a pressure of 100 mm. Gt; Art. Boiling occurs only at 62 ^o C.

Chemical properties

Reacting with metals and oxides, the substance shows its acid properties. Perfectly dissolving more complex compounds, the acid forms salts, which are called acetates: magnesium, lead, potassium, etc. The pK acid value is 4.75.

When interacting with gases, vinegar enters a substitution reaction with subsequent displacement and formation of more complex acids: chloroacetic acid, iodoacetic acid. Dissolving in water, the acid dissociates with the release of acetate ions and hydrogen protons. The degree of dissociation is 0.4 percent.

The physical and chemical properties of acetic acid molecules in a crystalline form create diamers on hydrogen bonds. Also, its properties are needed when creating more complex fatty acids, steroids and sterol biosynthesis.

Laboratory tests

Detect acetic acid in the solution can be due to the discovery of its physical properties, for example, odor. It is enough to add a stronger acid to the solution, which will begin to displace the salts of vinegar with the release of its vapors. By laboratory distillation of CH ₃ COONa and H ₂ SO _4, it is possible to obtain acetic acid in dry form.

We will draw experience from the school program on chemistry of the 8th grade. The physical properties of acetic acid clearly demonstrate the chemical reaction of dissolution. It is enough to add copper oxide into the solution to the substance and lightly heat it. Oxide completely dissolves, making a solution of bluish color.

Derivatives

Qualitative reactions of the substance with many solutions form: esters, amides and salts. However, during the production of other substances, the requirements for the physical properties of acetic acid remain high. It should always have a high degree of dissolution, and therefore, do not have third-party impurities.

Depending on the concentration of acetic acid of the aqueous solution, a number of its derivatives are isolated. Concentration of the substance more than 96% has the name - glacial acetic acid. Acetic acid in 70-80% can be purchased at grocery stores, where it will be called - acetic essence. Table vinegar has a concentration of 3-9%.

Acetic acid and everyday life

In addition to food features, acetic acid has a number of physical properties that humanity has found its use in everyday life. A solution of a substance of low concentration easily removes plaque from metal products, surfaces of mirrors and windows. The ability to absorb moisture also plays good. Vinegar nicely removes odors in musty rooms, removes stains from vegetables and fruits on clothing.

As it turned out, the physical property of acetic acid - to remove fat from the surface - can find application in folk medicine and cosmetology. A weak solution of food vinegar is treated with hair to give them shine. The substance is widely used for the treatment of colds, removal of warts and skin fungi. The use of vinegar as part of cosmetic wraps to fight cellulite is gaining momentum.

Use in production

In compounds of salts and other complex substances, acetic acid is an indispensable element:

• Pharmaceutical industry. To create: aspirin, antiseptic and antibacterial ointments, phenacetin.
• Manufacture of synthetic fibers. Non-combustible films, cellulose acetate.
• Food industry. For successful preservation, preparation of marinades and sauces, as food additive E260.
• Textile industry. It is part of the dyes.
• Manufacture of cosmetics and hygiene products. Aromatic oils, cream to improve skin tone.
• Manufacturing of mordants. Used as an insecticide and mordant against weeds.
• Manufacture of varnishes. Technical solvents, acetone production.

The production of acetic acid increases every year. Today its volume in the world is more than 400 thousand tons per month. The acid is transported in strong steel tanks. Storage in plastic containers at many production facilities in connection with the high physical and chemical activity of acetic acid is prohibited or limited to a period of several months.

Security

Acetic acid of high concentration has a third degree of ignition and releases toxic fumes. It is recommended to wear special gas masks and other personal protective equipment while working with acid. A lethal dose for the human body from 20 ml. At the time of ingestion, the acid first burns the mucous membrane, and then affects the other organs. In such cases, immediate hospitalization is needed.

After getting acid on the exposed areas of the skin, it is recommended to immediately wash them with running water. Surface burn with acid can cause tissue necrosis, which also requires hospitalization.

Interesting Facts

Scientists of physiology have found out, that the person at all is not obligatory acetic acid reception - it is possible to do without food additives. But people with acid intolerance, as well as with stomach problems, the substance is contraindicated.

Acetic acid is used in book printing.

The substance was found in small quantities in honey, bananas and wheat.

Cooling the acetic acid and sharply shaking the container with it, you can observe its sharp congealing.

A small concentration of acetic acid can reduce the pain symptom from an insect bite, as well as minor burns.

Admission to food products with low content of acetic acid reduces the level of cholesterol in the body. The substance stabilizes the level of sugar in diabetics well.

The use of protein and carbohydrate foods together with a small amount of acetic acid increases their digestibility by the body.

If the food is salted, just add a few drops of vinegar to smooth the salty.

Finally

Millennium use of acetic acid has led to the fact that its physical and chemical properties find their application at every step. Hundreds of possible reactions, thousands of useful substances, thanks to which humanity goes further. The main thing is to know all the features of acetic acid, its positive and negative qualities.

Do not forget about the benefits, but always remember what harm can cause careless handling of high-concentration acetic acid. By its peril, it stands next to hydrochloric and sulfuric acid. Always remember about safety when using acid. Properly and gently dilute the essence with water.