How alkalis are obtained in industry. Alkali: formula, properties, application. Industrial use of alkali

The word "acid" comes from the Latin word for "sour". Some foods from our table, for example, vinegar or lemon juice, - acids. A base is a compound chemically opposite to an acid, and upon reaction with an acid gives a neutral compound -. Bases that are soluble in water are called alkalis. Citrus fruits - grapefruits, oranges and lemons - contain citric and ascorbic acids. Bee venom is acid. You can neutralize it with a foundation. Citrus fruits - grapefruits, oranges, lemons - contain citric and ascorbic acids.

Acids

Acids are compounds that contain and form hydrogen ions (H +) when dissolved in. Ions are particles with an electric charge (see article ""). It is ions that give acids their properties, but they can exist only in solution. Consequently, the properties of acids appear exclusively in solutions. The sulfuric acid molecule (H 2 SO 4) is composed of hydrogen, sulfur and oxygen. Hydrochloric acid (HCl) contains hydrogen and chlorine. An acid is considered strong if most of its molecules disintegrate in solution, releasing hydrogen ions. Hydrochloric, sulfuric, nitric acids are strong. The strength of the acid is measured by the number of pH - hydrogen index... Strong acids are very aggressive; hitting the surface of an object or skin, they burn it. Containers with strong acids are labeled with globally accepted symbols meaning “dangerous” and “high activity”.

Acids such as citric or acetic, i.e. produced by living organisms are called organic... Acids are widely used in the chemical and medical industries, in the production of food and synthetic fibers. Grape vinegar contains a weak acid called acetic acid. Tomatoes contain organic salicylic acid. The colored spots on the skin of sea snails contain an unpleasant tasting acid that repels predators. All acids are characterized by a similar behavior in. For example, when acids react with bases, a neutral compound is formed - salt and water. Reactions of acids with the majority give salt and hydrogen. Acids react with carbonates to produce salt, carbon dioxide and water. The baking powder known to culinary experts contains sodium bicarbonate and tartaric acid. When water is added to flour containing baking powder, the acid and carbonate of the powder react, carbon dioxide starts to bubble out and this helps the dough rise.

Bases and alkalis

A base is a compound chemically opposite to acid. Alkali is a base that is soluble in water. Mixing with the acid, the base neutralizes its properties, and the salt is the reaction product. Toothpaste - a base that neutralizes the acid left in the mouth after eating. Household liquid cleaners contain alkalis that dissolve dirt. Stomach tablets contain alkalis that neutralize the acid that circulates during indigestion. From the point of view of chemistry, bases are substances capable of attaching hydrogen ions (H +) from an acid. Oxide ion (O 2-) and hydroxide ion (OH -) can combine with hydrogen ions in acid. This means that metal oxides, such as magnesium oxide, and metal hydroxides, such as sodium hydroxide (sodium hydroxide), are bases. Sodium hydroxide (NaOH) is composed of sodium, oxygen and hydrogen. Magnesium hydroxide (Mg (OH) 2) consists of magnesium, oxygen and hydrogen.

Many bases and alkalis are very caustic substances and therefore dangerous: they corrode living things. Liquid cleaners contain alkalis that dissolve dirt. In the paper industry, sodium hydroxide dissolves the tar and releases the cellulose fibers from which the paper is made. Sodium hydroxide (sodium hydroxide) is used in cleaning fluids and (like potassium hydroxide) to make soaps. Soap is a salt formed by the reaction of alkalis with acids from vegetable fats. The wasp's sting releases alkali, which can be neutralized with an acid such as vinegar.

pH and indicators

The strength of acids and bases is determined by the pH number. It is a measure of the concentration of hydrogen ions in a solution. The pH number varies from 0 to 14. The lower the pH, the higher the concentration of hydrogen ions. A solution with a pH of less than 7 is acid. Orange juice has a pH of 4, which means it is acid. Substances with pH \u003d 7 are neutral, and substances with a pH greater than 7 are bases or alkalis. The pH of an acid or alkali can be determined with an indicator. An indicator is a substance that changes color on contact with an acid or alkali. So litmus turns red in acid and turns blue in alkali. The acid turns the blue litmus paper red, and the red litmus paper turns blue or purple in alkali. Litmus is obtained from primitive plants called lichens... Other plants such as hydrangea and red cabbage are also natural indicators.

The so-called universal indicator is a mixture of several colors. It changes color depending on the pH of the substance. It turns red, orange or yellow in acids, green or yellow in neutral solutions, and blue or violet in alkalis.

Sulfuric acid

Sulfuric acid plays an important role in industry, primarily in the production of fertilizers based on superphosphates and ammonium sulfate. It is also used in the production of synthetic fibers, dyes, plastics, drugs, explosives, detergents, car batteries... Sulfuric acid was once called mineral acid, since it was obtained from sulfur - a substance found in the earth's crust in the form of a mineral. Sulfuric acid is very active and aggressive. When dissolved in water, it emits a lot of heat, so it must be poured into water, but not vice versa - then the acid will dissolve and the water will absorb the heat. She is a powerful oxidizing agent, i.e. during oxidation reactions, it gives up oxygen to other substances. Sulfuric acid is also a desiccant, i.e. takes away water associated with another substance. When sugar (C 12 H 22 O 11) dissolves in concentrated sulfuric acid, the acid takes water from the sugar, leaving a foaming mass of black coal from the sugar.

Acids in the soil

The acidity of the soil depends on the nature of the rocks that formed it and on the plants growing on it. On chalk and limestone rocks, the soil is usually alkaline, while in meadows, in sandy and wooded areas, it is more acidic. Acidity is also increased by acid rain. For agriculture, neutral or slightly acidic soils are best suited, the pH of which is from 6.5 to 7. When decomposed, dead leaves form organic humic acid and increase the acidity of the soil. Where the soils are too acidic, crushed limestone or hydrated lime (calcium hydroxide) is added to them, i.e. bases that neutralize soil acids. Plants such as rhododendrons and azaleas thrive on acidic soils. Hydrangea flowers are blue on acidic soil and pink on alkaline soil. Hydrangea is a natural indicator. On acidic soils, its flowers are blue, and on alkaline soils, pink.

Hello, friends. Today we will deal with this topic: acids and alkalis. To be more precise, then "than are alkalis different from acids? " Let's remember a little about chemistry. In general, acids and alkalis are such chemical elements that, when combined with each other (in the correct amount), create a process neutralization. This process eventually gives us water and salt.
And the result is a substance that does not belong to either acids or alkalis. It is not capable of causing burns. But this will only be with the correct proportion of acid and alkali (sometimes phenolphthalein is used for fidelity, it stains the alkali a slightly purple color).
Acid and alkali are like two opposites. But they are very important in the manufacture of things such as fertilizers, plastic, soaps, detergents, paints, paper and even explosives. This is not the entire list.
Acid - it is something sour, it is characterized by a sour taste. The acid is contained in vinegar - acetic acid, lemon - citric acid, milk - lactic acid, stomach - hydrochloric acid, etc. But these are all so-called weak acids, in addition to them, there are acids with a higher concentration (sulfuric acid, etc.). They are much more dangerous to humans and are not recommended for anyone to try. They can corrode clothing, skin, cause severe burns on the skin, and corrode concrete and other substances. For example, we need hydrochloric acid so that the stomach digests food faster, as well as to destroy most of the harmful bacteria that come with food.
Alkali - these are substances that dissolve well in water. In this case, the reaction is accompanied by the release of heat, with an increase in temperature. If alkali is compared with acid, then to the touch it is much more "soapy", that is, slippery. In general, alkalis are not far behind acids in terms of corrosion and strength. They can also easily eat wood, plastic, clothing and the like.
By the way, soap, glass, paper, fabric are made from alkalis, and this is not the whole list. Alkaline can be found in your kitchen, well, or in a store called baking soda. By the way, baking soda is a very good helper for all housewives.

Acids and alkalis are distinguished by their pH values \u200b\u200b(pH scale). Below you see a picture - this is a special scale on which there are numbers from 0 to 14. Zero denotes the most strong acids, and fourteen - the strongest alkali. But what is the middle between these numbers? Maybe 5, maybe 7, or maybe 10? The number 7 (neutral position) is considered to be the middle. That is, numbers up to 7 are all acids, and more than 7 are alkalis.

PH solution acidity index, mechanism of action

It is for this scale that special indicators have been developed. - litmus... This is a common strip that reacts to the environment. In an acidic environment, it stains in red, and in an alkaline environment - in blue. It is necessary not only in chemistry, but also in everyday life.

For example, if you have an aquarium, the acidity of the water plays an important role. The whole life of the aquarium depends on it. For example, the acidity index of water for aquarium fish ranges from 5 to 9 pH. If it is more or less, then the fish will feel uncomfortable, and may even die. Everything is the same with plants for aquariums ...

Working with acids and alkalis requires great care and attention. Indeed, when in contact with the skin, they cause severe burns. Try to work in a ventilated area. It is also not recommended to inhale vapors of alkalis and acids. For personal safety, you should use glasses, gloves and special clothing so as not to damage your eyes, hands and your favorite clothes)))
When working with acids it should be remembered that the acid is first poured into the solution (water), and not vice versa. Otherwise, a violent reaction will occur, which is accompanied by splashes. And the process of adding acid to the solution itself should be done very slowly, while controlling the degree of heating of the vessel and be sure to add acid along the walls of the vessel.
When working with alkalis the first one should add a little alkali (i.e. alkali to the water - right!). In addition, it is forbidden to use glassware, porcelain or special dishes are recommended.
When chemical processing metals (oxidation, anodizing, etching, etc.), immerse in the solution and remove the product from the solution using special devices or tools, but not with your hands, even if they are wearing rubber gloves. By the way, alkali is part of some

Instructions

Stock up on the starting materials for the preparation of alkali - caustic soda. For 1 kg of soda, take 0.9 kg of slaked lime. Prepare a solution of soda, for which dissolve 1 kg of soda in 4.5 liters of water.

Place the baking soda solution in the boiler (you can immediately dissolve the baking soda in the cooking pot). Heat the liquid to 60 ° C.

Pour slaked lime ("milk of lime") mixed with water into the boiler in small portions. Since the solution foams and can go over the edge, load the boiler two-thirds of it. Stir the liquid well during cooking; the more thoroughly the liquid is mixed, the better the quality of ordinary soda will be in caustic soda.

Heat the resulting mixture for an hour, then let it settle. Drain the clear solution from the sediment. This liquid is a sodium hydroxide solution or sodium hydroxide, the most common alkali (chemical formula NaOH). The sediment is undissolved lime, chalk and some impurities.

After removing the clear solution, add water to the remaining sediment and boil several times, and then let stand. Then again drain the clear liquid, which is a caustic soda solution, but of a lesser strength.

If a stronger alkali is needed to saponify the fat in order to make soap, the resulting solution should be evaporated. After the water evaporates, the alkali solution will become stronger. Accordingly, if for your needs an alkali of a lesser strength is needed, dilute the solution with water. With the described method homemade caustic soda from 1 kg of soda ash is about 0.8 kg of the final product.

Sources:

• How to prepare a potassium alkali solution

Alkalis are hydroxides of alkali, alkaline earth metals and ammonium. These include bases that are perfectly soluble in water. Anions OH− and a metal cation are formed during the dissociation of alkalis.

In the periodic system, alkalis include metal hydroxides of subgroups Ia and IIa (starting with calcium), for example, Ba (OH) 2 (caustic barite), KOH (caustic potassium), NaOH (caustic soda), which are commonly called “caustic alkalis”. Caustic alkalis are sodium hydroxides NaOH, lithium LiOH, rubidium RbOH, KOH and CsOH. They are solid and very hygroscopic substances. Alkalis with bases that dissolve well in water with significant heat release during the reaction. Water solubility and base strength increase with increasing cation radius in each group periodic system... The strongest alkalis are cesium hydroxide in group Ia and hydroxide in group IIa. An aqueous solution of ammonia gas, called ammonia Is weak alkali... Slaked lime is also sodium alkali... In addition, caustic alkalis can dissolve in methanol and ethanol. All solid alkalis absorb water and carbon dioxide from the air (and in solution), gradually converting to carbonates. When important chemical property - the ability to form salts in reaction with alkali acids are widely used in industry. They can conduct electric current, therefore they are also called electrolytes. Alkalis can be obtained by the action of water on alkali metal oxides or by electrolysis of chlorides. Properties of alkalis: dissolve fat, some of them can dissolve animal and plant tissues, destroy clothing and irritate the skin, can interact with some metals (aluminum), protect steel from corrosion. Alkalis and acids are dangerous, they must be stored only in special containers marked with labels, and never in drinking containers. Wear protective goggles when working.

Approximate solutions. The most common alkali solutions in laboratory practice are sodium hydroxide solutions NaOH. Potassium hydroxide solutions KOH are rarely prepared, while ammonia solutions are almost always bought ready-made.

Caustic soda (or caustic potassium) available on sale in the form of preparations: technical, pure and chemically pure. The difference between them lies in the percentage of NaOH (or KOH) 1 and, therefore, impurities. Technical * NaOH contains significant amounts of NaCl, Na2CO3, Na2SiO3, Fe2O3, etc. A pure reagent contains a minimum amount of these impurities, while a chemically pure reagent contains only traces of them.

Technical caustic soda is sold as cast in iron barrels, pure - in lamellar pieces, and chemically pure - in the form of sticks or tablets.

When the alkali dissolves, strong heating occurs, especially in those places where its pieces lie. To dissolve faster, the solution should be stirred all the time with a glass rod.

It is not recommended to use glassware when dissolving alkali, because it can easily break and the worker may be injured, as the concentrated alkali solution corrodes skin, shoes and clothes. If you have to prepare small amounts of alkali, you can dissolve it in glassware.

Pieces of alkali cannot be taken with bare hands, they should be taken with crucible tongs, special tweezers or, in extreme cases, with your hands, but always wearing rubber gloves.

* In the technique, caustic soda is often called caustic soda.

alkalis, many impurities do not dissolve and, when the solution settles, settle to the bottom. The settling of a concentrated alkali solution lasts for several days (at least two) *. The settled solution is carefully poured, best of all with a siphon, into another vessel, and the precipitate is thrown away or used for washing dishes.

If in the laboratory it is necessary to prepare alkali solutions often and in large quantities, then the following technique is used. First, the alkali is completely dissolved in a porcelain cup, and when the solution cools down a little (to 40-50 ° C), it is poured through a funnel into a glass bottle of a suitable container. The bottle is well closed with a rubber stopper equipped with an opening into which a calcium chloride tube filled with soda lime is inserted (to absorb carbon dioxide). When the alkali has settled and a sharply delimited layer of sediment forms at the bottom (1-2 cm from the bottom), the upper layer of the solution is poured into another bottle. Two tubes are inserted into the rubber stopper of the latter, one of which should enter approximately 1/3 of the height of the bottle, and the other should be 1-2 cm below the stopper (Fig. 350).

A rubber tube with a glass end is placed on the outer end of a long glass tube, which is lowered into a bottle with settled alkali. The lower end of this tube should be bent as shown in fig. 350. This end prevents sediment from being captured from the bottom of the bottle even if the end of the tube touches the sediment. The short tube is connected to a vacuum pump. By turning on the pump, the settled solution is quickly and safely pumped into another bottle. When pouring alkali, it is necessary to ensure that the tube, lowered into a vessel with settled alkali, does not pick up the sediment from the bottom. Therefore, at the beginning of the transfusion, it is kept high enough above the sediment, gradually lowering it towards the end of the transfusion.

After that, the density of the solution is determined with a hydrometer and the percentage of alkali is found from the table. If it is necessary to prepare a more dilute solution, then the dilution is carried out using the calculation methods described above.

* Naturally, the caustic soda solution must settle without carbon dioxide access to it. Concentrated alkali solutions strongly leach the glass of bottles, therefore the inside of the bottle must be covered with paraffin or a mixture of ceresin and petroleum jelly, or an alloy of paraffin with polyethylene (see chapter 3 “Stoppers and their handling”).

To cover the walls of the bottle with paraffin, several pieces of it are placed inside the bottle and the latter is heated in an oven or over electric stove or with a gas burner (carefully) up to 60-8O0C When the paraffin has melted, turn the bottle and spread the melted mass in a thin layer over the entire inner surface.

The wax or ceresin layer can be applied using a solution of these substances in aviation gasoline. Paraffin is first dissolved in gasoline, the resulting solution is poured into a bottle, which must be covered with paraffin inside. The walls of the bottle are washed with the introduced paraffin solution, slowly turning it "about the axis in a horizontal position. When a paraffin film forms on the glass, the bottle is blown with air until the gasoline vapor is completely displaced. Then the bottle is rinsed once or twice with water. Only then can it be filled with alkali or with another liquid.

The treatment of bottles for storing alkalis is especially important for analytical laboratories, as it prevents the contamination of titrated solutions with glass leaching products.

Precise solutions. The preparation of exact solutions differs in that they take chemically pure alkali for them, dissolve it, as indicated above, and determine the alkali content by titration with an exact acid solution.

The titer of a tickling solution (that is, the exact concentration of the solution) is best established by a solution of oxalic acid (C2H2O4 2H2O) *.

Commercial oxalic acid should be recrystallized once or twice and only then used to prepare an accurate solution. It is a dibasic acid and, therefore, its equivalent weight is half the molecular weight. Since the latter is 126.0665, its equivalent weight will be:

Cooking 0.1 and. NaOH solution, we must have a solution of oxalic acid of the same normality, for which we need to take it for 1 liter of solution:

But to set the titer, this amount of solution is not needed; it is enough to prepare 100 ml or a maximum of 250 ml. For this, about 0.63 g (for 100 ml) of recrystallized oxalic acid is weighed on an analytical balance to the fourth decimal place.

Novice workers, when taking samples for setting the titer, often try to weigh the amount of the substance exactly indicated in the manual (in our case, 0.6303 g). In no case should this be done, since such weighing inevitably requires multiple

* Since caustic soda easily absorbs carbon dioxide, sodium carbonate is always present in alkali... Having prepared a solution of caustic soda, it is imperative to set its concentration by titrating solutions of precise weighed amounts of organic acids, such as oxalic, malic, etc. Therefore, there is no need to dilute the concentrated solution in a volumetric flask to bring the solution level exactly to the mark; you can pour it into the bottle where it will be stored and add water with a graduated cylinder. It should be borne in mind that when preparing solutions of caustic alkalis, the main attention should be paid to protecting the solutions from carbon dioxide in the air. Any reduction in operations in which the solution can come into contact with air is highly desirable, pouring and pouring the substance into the container. As a result, a part of the substance falls on the scales and on outer wall containers and an accurately weighed amount of substance cannot be completely transferred into a volumetric flask. Therefore, the prepared solution will be inaccurate. Finally, very many substances change in the air (they lose crystallization water or, as they say, "erode", absorb carbon dioxide from the air, etc.). Therefore, the longer the weighing continues; the greater the possibility of contamination of the substance. Therefore, first, on a technochemical balance, a sample is taken that converges -\u003e the required one in the first two decimal places, and then the exact mass is determined on an analytical balance. The weighed portion is dissolved in an appropriate volume of solvent.

Knowing the mass of the substance taken and the volume of the solution, it is easy to calculate its exact concentration, which in our case will not be equal to 0.1 N, but slightly less. With this method, the calculation is somewhat complicated, but greater accuracy and significant time savings are achieved.

When the solution is ready, take 20 ml from it with a pipette, transfer it to a conical flask, add a few drops of phenolphthalein and titrate with the prepared alkali solution until a weak pink color appears.

Example. The titration consumed 22.05 ml of alkali solution. Calculate its titer and normality.

Oxalic acid was taken 0.6223 g instead of the theoretically calculated amount of 0.6303 g.Consequently, the concentration of its solution is not exactly 0.1 N., but equal

To calculate the normality of an alkali solution, use the ratio N)