How alkalis are produced in industry. Alkali: formula, properties, application. Industrial applications of alkali

The word "acid" comes from the Latin word for "sour". Some products from our table, for example, vinegar or lemon juice, - acids. A base is a compound that is chemically opposite to an acid, and when reacted with an acid, it gives a neutral compound -. Water-soluble bases are called alkalis. Citrus fruits - grapefruits, oranges, lemons - contain citric and ascorbic acids. Bee venom is an acid. You can neutralize it with a base. 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 the article ""). It is ions that give acids their properties, but they can only exist in solution. Consequently, the properties of acids appear exclusively in solutions. The sulfuric acid molecule (H 2 SO 4) consists 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 an acid is measured by the pH number - pH indicator. Strong acids are very aggressive; once on the surface of an object or on the skin, they burn through it. Containers with strong acids are marked with the symbols accepted all over the world, 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 acid with an unpleasant taste that repels predators. All acids are characterized by similar behavior in. For example, when acids react with bases, a neutral compound is formed - salt and water. Reactions of acids with most give salt and hydrogen. Reacting with carbonates, acids give salt, carbon dioxide and water. Known to culinary experts, baking powder 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 to rise.

Bases and alkalis

A base is a compound chemically opposite to an acid. An alkali is a base that is soluble in water. When mixed with an acid, the base neutralizes its properties, and the reaction product is a salt. Toothpaste- a base that neutralizes the acid left in the mouth after eating. Household liquid cleaners contain alkalis that dissolve dirt. Gastric 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. An oxide ion (O 2-) and a hydroxide ion (OH -) can combine with hydrogen ions in an acid. Hence, metal oxides, such as magnesium oxide, and metal hydroxides, such as sodium hydroxide (caustic soda), are bases. Sodium hydroxide (NaOH) consists 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 tree resin and frees the cellulose fibers from which paper is made. Sodium hydroxide (caustic soda) is used in cleaning fluids and (like potassium hydroxide) in soap making. Soap is a salt formed by the reaction of alkalis with acids of vegetable fats. The wasp's sting releases an alkali that 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 less than 7 is an acid. Orange juice has a pH of 4, which means it's an acid. Substances with a pH = 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 using an indicator. An indicator is a substance that changes color when it comes into contact with an acid or base. So litmus turns red in acid and blue in alkali. Acid turns blue litmus paper red, and 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 purple 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 manufacture 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 releases 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 heat. It is a powerful oxidizing agent, i.e. during oxidation reactions, it gives oxygen to other substances. Sulfuric acid is also a drying agent, i.e. takes in water bound to another substance. When sugar (C 12 H 22 O 11) is dissolved in concentrated sulfuric acid, the acid takes water from the sugar, and a foaming mass of black coal remains 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. Acid rain also increases acidity. For agriculture, neutral or slightly acidic soils are best suited, with a pH of 6.5 to 7. Decaying, dead leaves form organic humic acid and increase the acidity of the soil. Where soils are too acidic, crushed limestone or slaked lime (calcium hydroxide) is added to them, i.e. bases that neutralize soil acids. Plants such as rhododendrons and azaleas grow well in acidic soils. Hydrangea flowers are blue in acidic soil and pink in alkaline soil. Hydrangea is a natural indicator. Its flowers are blue in acidic soils and pink in alkaline soils.

Hello, friends. Today we will deal with the following topic: acids and alkalis. To be more precise, then "how Are alkalis different from acids? Let's think a little about chemistry. In general, acids and bases 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 cannot cause burns. But this will be only with the correct proportion of acid and alkali (sometimes phenolphthalein is used for fidelity, it colors the alkali in a slightly purple color).
Acid and alkali are like two opposites. But they are very important in the manufacture of such things as: fertilizers, plastics, soaps, detergents, paints, paper and even explosives. This is not the whole list.
Acid - this is something sour, it is characterized by a sour taste. Acid is found in vinegar - acetic acid, in lemon - citric acid, in milk - lactic acid, in the stomach - hydrochloric acid, etc. But it's all so-called weak acids, in addition to them, there are acids with a higher concentration (sulfuric acid, etc.). They are much more dangerous for a person and it is not recommended for anyone to try them. They can corrode clothing, skin, cause severe burns on the skin, 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 are highly soluble 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 it is much “soapier” to the touch, that is, slippery. In general, alkalis are not far behind acids in terms of corrosiveness and strength. They can also easily corrode wood, plastic, clothing, and the like.
By the way, soap, glass, paper, fabric are made from alkalis, and this is not the whole list. Alkali can be found in your kitchen, well, or in a store called baking soda. By the way, baking soda is very good helper to all housewives.

Acids and alkalis are distinguished by their pH values ​​(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 lye. But what is the middle between these numbers? Maybe 5, maybe 7, maybe 10? The middle is considered to be the number 7 (neutral position). That is, numbers up to 7 are all acids, and more than 7 are alkalis.

Acidity index of pH solutions, mechanism of action

It is for this scale that special indicators have been developed. - litmus. This is an ordinary strip that reacts to the environment. In an acid environment, it turns 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, then 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 there is more or less, then the fish will not feel comfortable, and may even die. It's the same with aquarium plants...

Working with acids and alkalis requires great care and caution. After all, when it comes into contact with the skin, they cause severe burns. Try to work in a ventilated area. Inhaling vapors of alkalis and acids is also not recommended. For personal safety, you should use glasses, gloves and special clothing so as not to damage your eyes, hands and 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 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 should be to add a little alkali (i.e. alkali to water - right!). In addition, it is forbidden to use glassware, porcelain or special dishes are recommended.
At chemical treatment metals (oxidation, anodizing, etching, etc.), the product should be immersed in the solution and removed 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

Instruction

Stock up on 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 soda solution in the cauldron (you can immediately dissolve the soda in the cauldron for cooking). Heat the liquid to 60°C.

Pour slaked lime (milk of lime) mixed with water into the cauldron in small portions. Since the solution foams and may overflow, load the boiler two-thirds of it. Stir the liquid well while cooking; the more thoroughly the liquid is mixed, the better the ordinary soda will turn into caustic soda.

Heat the resulting mixture for an hour, then let it settle. Drain the clear solution from the sediment. This liquid is 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 solution of caustic soda, but of a lower strength.

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

Sources:

• How to prepare a potassium lye solution

Alkalis are hydroxides of alkali, alkaline earth metals and ammonium. These include bases that are highly 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 potash), NaOH (caustic soda), bearing the philistine name "caustic alkalis". Caustic alkalis are sodium hydroxides NaOH, lithium LiOH, rubidium RbOH, KOH and CsOH. They are solid and very hygroscopic substances. Alkalis are 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 alkalis in the solid state absorb water and carbon dioxide from the air (and in the state of solution), gradually turning into carbonates. With important chemical property– the ability to form salts in reaction with alkali acids is widely used in industry. They can conduct electric current, so they are also called electrolytes. Alkalis can be obtained by exposing alkali metal oxides to water or by electrolyzing chlorides. Properties of alkalis: dissolve fat, some of them can dissolve animal and plant tissues, destroy clothes 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 in no case in drinking containers. Protective goggles should be worn when working.

approximate solutions. The most commonly used alkali solutions in laboratory practice are sodium hydroxide solutions NaOH. Solutions of caustic potash KOH are rarely prepared, but ammonia solutions are almost always bought ready-made.

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

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

When alkali is dissolved, strong heating occurs, especially in those places where pieces of it lie. To make the dissolution go 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 can be injured, since a concentrated solution of alkali corrodes skin, shoes and clothes. If you have to prepare small amounts of alkali, then you can dissolve it in glassware.

Chunks of lye with bare hands you can’t take them, they should be taken with crucible tongs, special tweezers or, in extreme cases, with your hands, but always with rubber gloves.

* In engineering, caustic soda is often called caustic soda.

alkalis, many impurities do not dissolve and, when the solution is settled, settle to the bottom. The settling of a concentrated alkali solution lasts several days (at least two) *. The settled solution is carefully drained, preferably by a siphon, into another vessel, and the precipitate is discarded or used for washing dishes.

If in the laboratory it is often necessary to prepare alkali solutions in large quantities, then the following method is used. First, the alkali is completely dissolved in a porcelain cup, and when the solution cools down a bit (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 provided with a hole into which a calcium chloride tube filled with soda lime (to absorb carbon dioxide) is inserted. When the alkali settles and a sharply demarcated layer of sediment forms at the bottom (1-2 cm from the bottom), the top 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. Such an end prevents the sediment from being captured from the bottom of the bottle, even if the end of the tube touches the sediment. A short tube is connected to a vacuum pump. Turning on the pump, the settled solution is quickly and safely pumped into another bottle. When transfusing alkali, care must be taken to ensure that the tube lowered into the vessel with settled alkali does not raise sediment from the bottom. Therefore, at the beginning of the transfusion, it is kept high enough above the sediment, gradually lowering 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 be settled without access to carbon dioxide. Strong alkali solutions strongly leach the glass of bottles, so the inside of the bottle must be coated with paraffin or a mixture of ceresin and vaseline, or an alloy of paraffin with polyethylene (see Ch. 3 "Clocks 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 gas burner (carefully) to 60-8O0C When the paraffin melts, turn the bottle and spread the melted mass in a thin layer over the entire inner surface.

A paraffin or ceresin layer can be applied by 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 inside with paraffin. 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 vapors are completely expelled. Then the bottle is rinsed once or twice with water. Only after that it can be filled with alkali or other liquid.

Treatment of alkali storage bottles is especially important for analytical laboratories, as it prevents contamination of titrated solutions by glass leaching products.

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

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

Sales 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 equal to 126.0665, then 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 it must be taken for 1 liter of solution:

But to set the titer, such an 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 test portions for setting the titer, often try to weigh out the exact amount of the substance indicated in the manual (in our case, 0.6303 g). In no case should this be done, since such weighing inevitably requires repeated

* Since caustic soda easily absorbs carbon dioxide, sodium carbonate is always present in alkali.. Having prepared a solution of caustic soda, its concentration must be determined by titrating solutions of accurate weights of organic acids, such as oxalic, malic, etc. Therefore, there is no need to dilute the concentrated solution in a volumetric flask with bringing the level of the solution exactly to the mark; you can pour it into the bottle where it will be stored, 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 may come into contact with air is highly desirable, pouring and pouring the substance into the container. As a result, part of the substance falls on the scales and on outer wall containers and accurately weighed amount of the substance cannot be completely transferred to the volumetric flask. Therefore, the prepared solution will be inaccurate. Finally, very many substances change in the air (lose water of crystallization or, as they say, “weather”, absorb carbon dioxide from the air, etc.). Therefore, the longer the weighing continues; the greater the potential for contamination. Therefore, first, a sample is taken on a technochemical balance that converges with the required one in the first two decimal places, and then the exact mass is determined on an analytical balance. The sample is dissolved in the 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 more 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 faint pink color appears.

Example. 22.05 ml of alkali solution was used for titration. Calculate its titer and normality.

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

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