Using sodium hydroxide solutions. Caustic soda: formula, properties, application

Sodium hydroxide is the well-known caustic soda, the most common alkali in the world. Chemical formula NaOH. Has others traditional names– caustic, caustic alkali, caustic soda, sodium hydroxide, sodium alkali.

Sodium hydroxide- This solid white or yellowish color, slightly slippery to the touch, which is obtained by electrolysis from sodium chloride. Sodium hydroxide is strong alkali, which is capable of destroying organic matter: paper, wood, and also human skin, causing burns varying degrees gravity.

Properties of sodium hydroxide

The industry produces sodium hydroxide in the form of a white, odorless, crumbly powder. Technical caustic soda can be supplied in the form various solutions: mercury, chemical, diaphragm. Usually it is a colorless or slightly colored liquid, hermetically sealed in an alkali-resistant container. Granular sodium hydroxide is also produced, which serves various technical needs.

Caustic is a water-soluble substance that, upon contact with water, releases a large number of warmth. The sodium lye solution is slightly slippery to the touch, reminiscent of liquid soap.

Other properties of sodium hydroxide

Insoluble in acetone, ethers;
It dissolves well in glycerin, ethanol and methanol (alcohol solutions);
Caustic is very hygroscopic, so soda must be packaged in a waterproof container and stored in a dry place;
Non-flammable, melting point - 318°C;
Boiling point - 1390°C;
The dangerous property of sodium hydroxide is its violent reaction upon contact with metals such as aluminum, zinc, lead, and tin. Being strong foundation, caustic soda can form explosive flammable gas(hydrogen);
A fire hazard also arises when sodium alkali comes into contact with ammonia;
When molten, it can destroy porcelain and glass.

On an industrial scale, this substance should be used carefully, since failure to comply with safety measures is dangerous for humans.

Applications of sodium hydroxide

IN Food Industry sodium alkali is known as food supplement– acidity regulator E-524. It is used in the production of cocoa, caramel, ice cream, chocolate and lemonade. Caustic soda is also added to bakery products and baked goods for a more fluffy consistency, and treating the products with caustic soda solution before baking helps to acquire a crispy, golden brown crust.

The use of sodium hydroxide is advisable to obtain a delicate and soft consistency of products. For example, soaking fish in alkaline solution allows you to obtain a jelly-like mass from which lutefisk is prepared - a traditional Scandinavian dish. The same method is used to soften olives.

Sodium hydroxide is used quite widely in the cosmetics industry. In the production of personal care products (soaps, shampoos, creams), as well as detergents, sodium hydroxide is necessary for saponification of fats and is present as an emulsifying alkaline additive.

Other uses of sodium hydroxide:

In the pulp and paper industry;
For the production of oils and the production of biodiesel in the oil refining industry;
For disinfection and sanitization premises, since caustic soda has the property of neutralizing substances in the air that are harmful to humans;
In everyday life for cleaning clogged pipes, as well as for eliminating contamination from various surfaces(tiles, enamel, etc.).

Why is caustic soda dangerous?

When it comes into contact with human skin, mucous membranes or eyes, sodium hydroxide causes quite severe chemical burns. It is necessary to immediately wash the affected area of the body big amount water.

If accidentally swallowed, it causes damage (chemical burns) to the larynx, oral cavity, stomach and esophagus. As first aid, you can give the victim a drink of water or milk.

Important Features of Sodium Hydroxide

It is important to know them so that working with this reagent is safe and that its use brings the expected results.

“Like other alkalis, this chemical is a strong base, which is known to dissolve well in water, which is accompanied by a strong release of heat.
— Sodium hydroxide can literally dissolve when exposed to air, as it is incredibly hygroscopic and absorbs moisture from environment. This means that it must be stored in a tightly sealed container and in a dry place. Sometimes it is stored as a solution in water, ethyl or methanol.
— It is not advisable to place a hot solution or molten reagent in containers made of glass or porcelain - this can damage them, since the caustic reacts with the silica in their composition. It is better to buy a container made of polyethylene, polyvinyl chloride or rubber for sodium hydroxide.

Main applications of caustic soda

— Soap making, production of paper and cardboard, cosmetics, solvents, biodiesel fuel and mineral oils.
— Wood processing, neutralization of toxic gases and acids.
— In medicine: removal of keratinized skin and papillomas, treatment of warts.
— As a cleaning and disinfectant, in chemical industry as a catalyst.
— In the food industry, in particular to give dark color and softness to olives, to obtain a crispy crust in baked goods, and in the production of cocoa.

Safety precautions when working with sodium hydroxide

According to GOST 12.1.007-76, caustic soda belongs to toxicity class II (highly hazardous). May cause severe burns to the skin and mucous membranes and irreversible damage to vision if it gets into the eyes. That is why you need to work with it wearing gloves and safety glasses, and using special vinyl-impregnated or rubberized clothing.

If the substance gets on the mucous membrane, it should be washed as soon as possible with plenty of running water, and the skin should be washed with a weak solution of vinegar.

If the burn surface is large, or if the reagent gets inside or into the eye, you should not only take these measures, but also immediately consult a doctor.

You can buy sodium hydroxide alkali in our store and we hope you will follow safety precautions. The product is sold with delivery, so you can buy alkali in Moscow or another city in Russia and soon receive it in your city.

Introduction

You came to the store, trying to buy unscented soap. Naturally, in order to understand which products from this range have a smell and which do not, you pick up each bottle of soap and read its composition and properties. Finally we chose the right one, but while watching various compositions Soap producers noticed a strange trend - almost all the bottles were written: “The structure of the soap contains sodium hydroxide.” This is the standard story of most people's introduction to sodium hydroxide. Some half of the people will “spit and forget,” and some will want to know more about him. It is for them that today I will tell you what this substance is.

Definition

Sodium hydroxide (formula NaOH) is the most common alkali in the world. For reference: alkali is a base that is highly soluble in water.

Name

IN different sources it may be called sodium hydroxide, caustic soda, caustic soda, caustic soda or caustic alkali. Although the name "caustic alkali" can be applied to all substances in this group. Only in the 18th century were they given separate names. There is also an “inverted” name for the substance now described - sodium hydroxide, usually used in Ukrainian translations.

Properties

As I already said, sodium hydroxide is highly soluble in water. If you put even a small piece of it in a glass of water, after a few seconds it will ignite and hissingly “scurry” and “jump” across its surface (photo). And this will continue until he completely dissolves in it. If, after the reaction is complete, you dip your hand into the resulting solution, it will be soapy to the touch. To find out how strong the alkali is, indicators - phenolphthalein or methyl orange - are dipped into it. Phenolphthalein in it becomes crimson in color, and methyl orange turns yellow. Sodium hydroxide, like all alkalis, contains hydroxide ions. The more of them in solution, the brighter color indicators and stronger alkali.

Receipt

There are two ways to obtain sodium hydroxide: chemical and electrochemical. Let's take a closer look at each of them.

Application

Delignification of cellulose, production of cardboard, paper, fiberboard and man-made fibers cannot be done without sodium hydroxide. And when it reacts with fats, soap, shampoos and other products are obtained. detergents. In chemistry, it is used as a reagent or catalyst in many reactions. Sodium hydroxide is also known as food additive E524. And this is not all the areas of its application.

Conclusion

Now you know everything about sodium hydroxide. As you can see, it brings very great benefits to people - both in industry and in everyday life.

Sodium hydroxide, or caustic soda - inorganic compound, which belongs to the class of bases, or hydroxides. Also in technology and abroad, this substance is called the trivial name - caustic soda - it received because of its strong corrosive effect.

It's solid crystalline substance white, which is hygroscopic, melting at a temperature of 328 degrees. Sodium hydroxide is highly soluble in water and is strong electrolyte. Upon dissociation, it decomposes into a metal cation and hydroxide ions.

When dissolved in water it forms active substance- alkali, - soapy to the touch. This reaction proceeds very violently - with splashing and heat generation. It is the contact of alkali on the skin and mucous membranes that causes severe chemical burns, so when working you need to be careful and protect your hands and eyes. When hit of this substance on the epithelium or in the eyes, mouth, it is necessary to rinse the affected areas as quickly as possible with water and a weak solution of acetic (2%) or boric (3%) acid, and then again with water. After rendering emergency care the victim must be shown to a doctor.

Sodium hydroxide (formula chemical compound- NaOH, structural - Na-O-H) is a chemically active substance that can react with both inorganic and hydroxide ions with various indicators. Thus, the litmus indicator becomes dark blue, methyl orange - yellow, and phenolphthalein - crimson, and the intensity of the color will depend on the concentration of the alkali.

Sodium hydroxide undergoes the following reactions:

1. neutralization with acids and amphoteric compounds. The result of this reaction is the formation of water and salt or hydroxo complex - in the case of interaction with amphoteric bases and oxides;

2. exchange with salts;

3. with metals that are located before hydrogen in the Beketov series and have a low electrochemical potential;

4. with non-metals and halogens;

4. hydrolysis with esters;

5. saponification with fats (soap and glycerin are formed);

6. interactions with alcohols (alcoholates are formed).

Also, in molten form, caustic soda can destroy porcelain and glass, and with access to oxygen - noble metal(platinum).

Sodium hydroxide can be obtained in the following ways:

electrolysis of water NaCl solution(diaphragm and membrane method),
chemical (lime and ferrite method).

IN last years methods based on electrolysis are most often used, because they are more profitable.

Caustic soda is very popular and is used in many industries - cosmetics, pulp and paper, chemicals, textiles, food. It is used as an additive E-524, for degassing premises and in the production of biodiesel fuel.

Thus, sodium hydroxide is an alkali that has found widespread use in various industries economic activity humans due to its chemically active nature.

Introduction .

Sodium hydroxide or caustic soda (NaOH), chlorine, hydrochloric acid HC1 and hydrogen are currently produced industrially by the electrolysis of sodium chloride solution.

Caustic soda or sodium hydroxide - a strong alkali, called caustic soda in everyday life, is used in soap making, in the production of alumina - an intermediate product for the production of aluminum metal, in the paint and varnish industry, oil refining industry, in the production of rayon, in industry organic synthesis and other sectors of the national economy.

When working with chlorine, hydrogen chloride, hydrochloric acid and caustic soda, it is necessary to strictly follow safety rules: inhalation of chlorine causes a sharp cough and suffocation, inflammation of the mucous membranes of the respiratory tract, pulmonary edema, and the subsequent formation of inflammatory foci in the lungs.

Hydrogen chloride, even at low levels in the air, causes irritation in the nose and larynx, tingling in the chest, hoarseness and suffocation. At chronic poisoning Low concentrations of it especially affect teeth, the enamel of which is quickly destroyed.

Hydrochloric acid poisoning is very similar With chlorine poisoning.

Chemical methods for producing sodium hydroxide.

TO chemical methods The production of sodium hydroxide includes calcareous and ferritic.

The lime method for producing sodium hydroxide involves reacting a solution of soda with milk of lime at a temperature of about 80°C. This process is called causticization; it is described by the reaction

Na 2 C0 3 + Ca (OH) 2 = 2NaOH + CaC0 3 (1)

solution precipitate

Reaction (1) produces a solution of sodium hydroxide and a precipitate of calcium carbonate. The calcium carbonate is separated from the solution, which is evaporated to produce a molten product containing about 92% NaOH. Molten NaOH is poured into iron drums where it hardens.

The ferritic method is described by two reactions:

Na 2 C0 3 + Fe 2 0 3 = Na 2 0 Fe 2 0 3 + C0 2 (2)

sodium ferrite

Na 2 0 Fe 2 0 3 -f H 2 0 = 2 NaOH + Fe 2 O 3 (3)

solution precipitate

reaction (2) shows the sintering process soda ash with iron oxide at a temperature of 1100-1200°C. In this case, sintered sodium ferrite is formed and carbon dioxide is released. Next, the cake is treated (leached) with water according to reaction (3); a solution of sodium hydroxide and a precipitate of Fe 2 O 3 are obtained, which, after separating it from the solution, is returned to the process. The solution contains about 400 g/l NaOH. It is evaporated to obtain a product containing about 92% NaOH.

Chemical methods for producing sodium hydroxide have significant disadvantages: a large amount of fuel is consumed, the resulting caustic soda is contaminated with impurities, maintenance of the devices is labor-intensive, etc. Currently, these methods are almost completely replaced by the electrochemical production method.

The concept of electrolysis and electrochemical processes.

Electrochemical processes are called chemical processes flowing in aqueous solutions or melts under the influence of constant electric current.

Solutions and molten salts, solutions of acids and alkalis, called electrolytes, belong to the second type of conductors in which the transfer of electric current is carried out by ions. (In conductors of the first kind, for example metals, current is carried by electrons.) When electric current passes through an electrolyte, ions are discharged at the electrodes and the corresponding substances are released. This process is called electrolysis. The apparatus in which electrolysis is carried out is called an electrolyzer or electrolytic bath.

Electrolysis is used to produce a number of chemical products - chlorine, hydrogen, oxygen, alkalis, etc. It should be noted that electrolysis produces chemical products high degree of purity, in some cases unattainable with chemical methods their production.

To the disadvantages electrochemical processes should be attributed to the high energy consumption during electrolysis, which increases the cost of the resulting products. In this regard, it is advisable to carry out electrochemical processes only on the basis of cheap electrical energy.

Raw materials for the production of sodium hydroxide.

To produce sodium hydroxide, chlorine, hydrogen, a solution is used table salt, which is subjected to electrolysis Table salt occurs in nature in the form of underground deposits rock salt, in the waters of lakes and seas and in the form of natural brines or solutions. Rock salt deposits are located in the Donbass, the Urals, Siberia, Transcaucasia and other areas. Some lakes in our country are also rich in salt.

IN summer time Water evaporates from the surface of the lakes, and table salt precipitates in the form of crystals. This type of salt is called self-settling salt. IN sea water contains up to 35 g/l sodium chloride. In places with a hot climate, where intense evaporation of water occurs, concentrated solutions of sodium chloride are formed, from which it crystallizes. In the bowels of the earth, in the layers of salt flow The groundwater, which dissolve NaCl and form underground brines that emerge through boreholes to the surface.

Solutions of table salt, regardless of the route of their production, contain impurities of calcium and magnesium salts and, before they are transferred to the electrolysis workshop, are purified from these salts. Cleaning is necessary because poorly soluble calcium and magnesium hydroxides can be formed during the electrolysis process, which disrupt the normal course of electrolysis.

Cleaning brines is done with a solution of soda and lime milk. Besides chemical cleaning, solutions are freed from mechanical impurities by settling and filtration.

Electrolysis of solutions of table salt is carried out in baths with a solid iron (steel) cathode and with diaphragms and in baths with a liquid mercury cathode. In any case, industrial electrolyzers used to equip modern large chlorine shops must have high performance, a simple design, be compact, operate reliably and steadily.

Electrolysis of sodium chloride solutions in baths with a steel cathode and graphite anode .

Makes it possible to produce sodium hydroxide, chlorine and hydrogen in one apparatus (electrolyzer). When a direct electric current passes through an aqueous solution of sodium chloride, one can expect the release of chlorine:

2CI - - 2eÞ C1 2 (a)

as well as oxygen:

20N - - 2eÞ 1/2O 2 + H 2 O(b)

H 2 0-2eÞ1/2О 2 + 2H +

Normal electrode potential discharge of OH - ions is + 0.41 V, and the normal electrode potential for the discharge of chlorine ions is + 1.36 V. In a neutral saturated solution of sodium chloride, the concentration of hydroxyl ions is about 1 10 - 7 g-eq/l. At 25° C, the equilibrium discharge potential of hydroxyl ions will be

Equilibrium discharge potential, chlorine ions at a NaCl concentration in solution of 4.6 g-eq/l equals

Therefore, oxygen should be discharged first at the anode with low overvoltage.

However, on graphite anodes, the oxygen overvoltage is much higher than the chlorine overvoltage and therefore, mainly the discharge of C1 ions will occur on them - with the release of chlorine gas according to reaction (a).

The release of chlorine is facilitated by increasing the concentration of NaCI in the solution due to a decrease in the value of the equilibrium potential. This is one of the reasons for use in electrolysis concentrated solutions sodium chloride containing 310-315 g/l.

At the cathode in an alkaline solution, water molecules are discharged according to the equation

H 2 0 + e = H + OH - (c)

Hydrogen atoms, after recombination, are released as molecular hydrogen

2Н Þ Н 2 (g)

Discharge of sodium ions from aqueous solutions on a solid cathode is impossible due to their higher discharge potential compared to hydrogen. Therefore, the hydroxide ions remaining in the solution form an alkali solution with sodium ions.

The decomposition process of NaCl can be expressed in this way by the following reactions:

that is, chlorine is formed at the anode, and hydrogen and sodium hydroxide are formed at the cathode.

During electrolysis, along with the main processes described, side processes can also occur, one of which is described by equation (b). In addition, chlorine released at the anode is partially dissolved in the electrolyte and hydrolyzed by the reaction

In the case of diffusion of alkali (OH - ions) to the anode or displacement of cathode and anodic products, hypochlorous and hydrochloric acid neutralized with alkali to form hypochlorite and sodium chloride:

HOC1 + NaOH = NaOCl + H 2 0

HC1 + NaOH = NaCl + H 2 0

ClO - ions at the anode are easily oxidized into ClO 3 -. Consequently, due to side processes during electrolysis, sodium hypochlorite, chloride and sodium chlorate will be formed, which will lead to a decrease in current efficiency and energy efficiency. In an alkaline environment, the release of oxygen at the anode is facilitated, which will also worsen electrolysis performance.

To reduce the occurrence of side reactions, conditions should be created that prevent the mixing of cathodic and anodic products. These include separation of the cathode and anode spaces by a diaphragm and filtration of the electrolyte through the diaphragm in the direction opposite movement OH - ions to the anode. Such diaphragms are called filter diaphragms and are made of asbestos.