Caustic soda- the most common alkali, the volume of production and consumption of which per year is up to 57 million.
Pure sodium hydroxide NaOH is a white, opaque mass that greedily absorbs water vapor and carbon dioxide from the air.
There are two modifications of anhydrous sodium hydroxide - α-NaOH with rhombic crystals and β-NaOH with cubic crystals. With water, NaOH forms a series of crystalline hydrates: NaOH * H 2 O, where n \u003d 1, 2, 2.5, 3.5, 4, 5.25 and 7.
Melting point = 323 gr. C, boiling point = 1403 gr. WITH.
Density = 2.02 g/cm 3 .
Aqueous solutions of NaOH have a strong alkaline reaction (pH 1% solution = 13).
This is very strong chemical base, enters into reactions characteristic of typical bases.
Interacts with various substances in any state of aggregation, from solutions and gases to solids - neutralization reactions. It reacts with acids, with amphoteric oxides (in solution and melt), with acid oxides - with the formation of salts.
For instance:
2NaOH + 2HCl = 2NaCl + H 2 O
ZnO + 2NaOH (melt) = Na 2 ZnO 2 + H 2 O
ZnO + 2NaOH (solution) + H 2 O = Na 2 + H 2
2NaOH + CO 2 \u003d Na 2 CO 3 + H 2 O (with an excess of NaOH)
Interaction with acid oxides is used to clean industrial emissions from acid gases (for example: CO 2 , SO 2 and H 2 S).
How strong alkali NaOH displaces weaker bases from salts:
2NaOH + CoCl 2 = 2NaCl + Co(OH) 2
This property is used to precipitate metal hydroxides with caustic soda.
For example, in this way water is purified from small suspensions (gel-like aluminum hydroxide is obtained by acting with sodium hydroxide on aluminum sulfate in an aqueous solution).
6NaOH + Al 2 (SO 4) 3 \u003d 2Al (OH) 3 + 3Na 2 SO 4.
Sodium hydroxide also reacts with non-metals:
3S + 6NaOH → 2Na 2 S + Na 2 SO 3 + 3H 2 O
2NaOH + Cl 2 \u003d NaClO + NaCl + H 2 O
and metals(having a high electrochemical potential):
2Al + 2NaOH + 6H 2 O = 3H 2 + 2Na
So alcohols forms alcoholates:
HO-CH 2 -CH 2 OH + 2NaOH → NaO-CH 2 -CH 2 -ONa + 2H 2 O
Participates in reactions hydrolysis(reaction with esters, amides and alkyl halides):
ROOR 1 + NaOH = ROONa + R 1 OH (ether + sodium hydroxide = sodium carboxylate + alcohol)
This property of alkali is widely used in industry, in the production of solid soap (in the case of interaction of sodium hydroxide with soap ( saponification) the reaction is irreversible):
(C 17 H 35 COO) 3 C 3 H 5 + 3NaOH \u003d C 3 H 5 (OH) 3 + 3C 17 H 35 COONa
The product is very aggressive! It destroys glass and porcelain by interacting with the silicon dioxide they contain ( silicate leaching): 2NaOH + SiO 2 = Na 2 SiO 3 + H 2 O, as well as materials of organic origin (paper, leather, etc.).
Hazard Class
Caustic soda is a corrosive substance. Causes chemical burns on skin, and prolonged exposure can cause ulcers and eczema. Strong effect on mucous membranes. It is dangerous to get caustic soda into the eyes. Maximum Permissible Concentration aerosol of caustic soda in the air of the working area of industrial premises (MPC) - 0.5 mg/m3.
Caustic soda is fire and explosion-proof, belongs to hazardous substances of the 2nd hazard class according to GOST 12.1.007.
Packing, transportation, storage
Technical caustic soda is transported by rail, road, water transport in covered vehicles in packaging and in bulk in rail and road tanks in accordance with the rules for the carriage of goods in force for this type of transport.
By rail, the product is transported in barrels, drums, boxes per carload.
Technical caustic soda intended for the medical industry and the production of artificial fibers, at the request of the consumer, is transported in railway tanks with stainless steel or gummed boilers belonging to the consumer or manufacturer.
Tanks are filled with caustic soda to full capacity, taking into account the volumetric expansion of the product with a possible temperature difference along the route.
Before filling tanks with the residue of sodium hydroxide solution, the residue shall be analyzed for compliance with the requirements of this standard. If the analysis of the residue is in accordance with the requirements of this standard, then the tank is filled with the product; if the analysis of the residue does not comply with the requirements of this standard, then the residue is removed and the tank washed.
Technical caustic soda, packed in specialized containers, is transported only by road.
The product packed in barrels, drums and boxes is transported in packaged form in accordance with GOST 26663, GOST 24957, GOST 21650, GOST 21140, on pallets in accordance with GOST 9557 and GOST 26381.
A solution of technical caustic soda is stored in closed containers made of a material resistant to alkalis.
The packaged product is stored in unheated warehouses.
Application
Caustic soda is widely used in a wide variety of industries and for domestic needs.
- In the chemical and petrochemical industry (they account for about 57% of the total Russian consumption of NaOH) - for the neutralization of acids and acid oxides, as a reagent or catalyst in chemical reactions, in chemical analysis for titration, for etching aluminum and in the production of pure metals , in oil refining - for the production of oils.
- Caustic is used in the pulp and paper industry for the delignification (sulphate process) of cellulose, in the production of paper, cardboard, artificial fibers, wood fiber boards.,
- For saponification of fats in the production of soap, shampoo and other detergents.
- In the production of biodiesel fuel derived from vegetable oils and used to replace conventional diesel fuel.
- As an agent for dissolving blockages in sewer pipes, in the form of dry granules or as part of gels. Sodium hydroxide disaggregates the blockage and facilitates its easy movement further down the pipe.
- Degassing and neutralization of toxic substances, including sarin, in rebreathers (isolated breathing apparatus (IDA), for cleaning exhaled air from carbon dioxide.
- In the food industry: for washing and peeling fruits and vegetables, in the production of chocolate and cocoa, drinks, ice cream, caramel coloring, for softening olives and in the production of bakery products. Registered as food additive E524.
- In non-ferrous metallurgy, energy, in the textile industry, for the regeneration of rubber.
RECEIVING
At the beginning of the 19th century, the production of caustic soda (NaOH) was closely connected with the development of the production of soda ash. This relationship was due to the fact that soda ash served as a raw material for the chemical method of obtaining NaOH, which was causticized with lime milk in the form of a soda solution. At the end of the 19th century, electrochemical methods for obtaining NaOH by electrolysis of aqueous solutions of NaCl began to develop rapidly. With the electrochemical method of production, simultaneously with NaOH, chlorine is obtained, which is widely used in the heavy organic synthesis industry and in other industries, which explains the rapid development of the electrochemical production of NaOH.
Today, caustic soda is produced either by electrolysis of a sodium chloride (NaCl) solution to form sodium hydroxide and chlorine, or, more rarely, by an older process based on the interaction of a soda ash solution with slaked lime. A large amount of soda ash produced in the world is used to produce caustic soda.
Interaction of soda ash solution with slaked lime.
Caustic soda is obtained from soda ash in a batch or continuous plant. The process is usually carried out at moderate temperatures in reactors equipped with agitators. The caustic soda formation reaction is an exchange reaction between sodium carbonate and calcium hydroxide:
Na 2 CO 3 + Ca (OH) 2 \u003d CaCO 3 + 2NaOH
The calcium carbonate precipitates and the sodium hydroxide solution is discharged into a collector.
electrolysis methods.
On an industrial scale, sodium hydroxide is obtained by electrolysis of solutions of halite (rock salt NaCl) with the simultaneous production of hydrogen and chlorine:
2NaCl + 2H 2 O \u003d H 2 + Cl 2 + 2NaOH
When a concentrated solution of sodium chloride is electrolyzed, chlorine and sodium hydroxide are formed, but they react with each other to form sodium hypochlorite, a bleaching agent. This product, in turn, especially in acidic solutions at elevated temperatures, is oxidized in the electrolysis chamber to sodium perchlorate. To avoid these undesirable reactions, electrolytic chlorine must be spatially separated from sodium hydroxide.
In most industrial plants used to produce electrolytic caustic soda, this is done using a diaphragm ( diaphragm method) placed near the anode where chlorine is formed. There are two types of installations: with a submerged or non-immersed diaphragm. The chamber of the installation with a submerged diaphragm is completely filled with electrolyte. The brine flows into the anode compartment, where chlorine is released from it, and the caustic soda solution fills the cathode compartment. In an unimmersed diaphragm plant, the caustic soda solution is removed from the cathode compartment as it forms, so that the chamber is empty. In some non-immersed diaphragm installations, steam is forced into the empty cathode compartment to facilitate removal of the caustic soda and raise the temperature.
Diaphragm plants produce a solution containing both caustic soda and salt. Most of the salt crystallizes out when the concentration of caustic soda in the solution is brought to the standard value of 50%. This "standard" electrolysis solution contains 1% sodium chloride. The electrolysis product is suitable for many applications, such as the production of soap and cleaning products. However, the production of artificial fiber and film requires highly purified caustic soda containing less than 1% sodium chloride (salt). "Standard" liquid caustic can be properly purified by crystallization and precipitation methods.
Membrane method- similar to diaphragm, but the anode and cathode spaces are separated by a cation exchange membrane. Membrane electrolysis provides the purest caustic.
Continuous separation of chlorine and caustic can also be carried out in a mercury cathode unit ( mercury electrolysis). Metallic sodium forms an amalgam with mercury, which is discharged into the second chamber, where sodium is released and reacts with water, forming caustic and hydrogen. Although the concentration and purity of the brine is more important for a mercury cathode plant than for a diaphragm plant, the former produces caustic soda suitable for man-made fiber production. Its concentration in solution is 50–70%. The higher cost of a mercury cathode plant is justified by the benefits.
Literature:
GOST 2263-79: Technical caustic soda. Specifications. - M., IPK Publishing house of standards, 2001; Popular library of chemical elements. - M., Nauka, 1977; Technology of inorganic substances and mineral fertilizers: a course of lectures. - Department of Chemistry and Ecology of NovSU, 2007; Fundamentals of General Chemistry, v. 3, B. V. Nekrasov. - M., Chemistry, 1970; General chemical technology. Furmer I. E., Zaitsev V. N. - M., Higher School, 1978
Introduction
You came to the store looking 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, they chose the right one, but while looking at the various compositions of the soap, they noticed a strange trend - on almost all the bottles it was written: "Soap contains sodium hydroxide in the structure." This is the standard history of most people's acquaintance with sodium hydroxide. Some half of the people will "spit and forget", and some will want to know more about him. So for them today I will tell you what kind of substance it 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 various sources, it can be called sodium hydroxide, caustic soda, caustic, caustic soda or caustic alkali. Although the name "caustic alkali" can be applied to all substances in this group. Only in the XVIII century they were given separate names. There is also an "inverted" name of the substance described now - sodium hydroxide, usually used in Ukrainian translations.
Properties
As I 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 will “rush” and “jump” along its surface with a hiss (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 are lowered into it - phenolphthalein or methyl orange. Phenolphthalein in it acquires a crimson color, and methyl orange - yellow. Sodium hydroxide, like all alkalis, contains hydroxide ions. The more of them in the solution, the brighter the color of the indicators and the stronger the alkali.
Receipt
There are two ways to obtain sodium hydroxide: chemical and electrochemical. Let's consider each of them in more detail.
Application
The delignification of cellulose, the production of cardboard, paper, fibreboard and artificial fibers cannot do without sodium hydroxide. And when it reacts with fats, soap, shampoos and other detergents are obtained. In chemistry, it is used as a reactant or catalyst in many reactions. Sodium hydroxide is also known as food additive E524. And this is not all areas of its application.
Conclusion
Now you know everything about sodium hydroxide. As you can see, it brings a lot of benefits to a person - both in industry and in everyday life.
With a chemical compound called caustic soda, a person encounters daily. Sodium hydroxide, the chemical formula of which is designated NaOH, belongs to the category of caustic and strong alkalis that are dangerous to the skin and mucous membranes of a person. At the same time, it is actively used by the food industry, cosmetology, and pharmaceuticals. No personal care product is complete without the addition of this compound. The chemical properties of the substance have made it the most popular acidity regulator and consistency agent.
What is sodium hydroxide
This compound is a caustic alkali, which is used not only in the food, pharmaceutical and cosmetic fields, but also in the chemical industry. Sodium hydroxide, or caustic soda, comes in the form of slightly slippery, hard, yellowish or white granules. With a strong NaOH concentration corrodes organic compounds, therefore it can cause a burn. It is used as a food additive E524, necessary to maintain the consistency of products.
Formula
The substance has the chemical formula NaOH. The compound interacts with various substances of any state of aggregation, neutralizing them, with acids, forming salt and water. Reaction with atmospheric oxides and hydroxides produces tetrahydroxozincate or alcoholate. Caustic soda is used to precipitate metals. For example, when reacting with aluminum sulfate, its hydroxide is formed. The precipitate does not dissolve and there is no excess production of alkali. This is true when purifying water from small suspensions.
Properties
The compound is soluble in water. Technical Sodium Hydroxide is aqueous sodium hydroxide solution in an alkali-resistant sealed container. When interacting with water, the caustic releases a large amount of heat. The substance has the following properties:
- during preliminary melting destroys glass, porcelain;
- interaction with ammonia causes a fire hazard;
- boils at 1390°C, melts if the temperature reaches 318°C;
- insoluble in ethers, acetone;
- very hygroscopic (absorbs water vapor from the air), so sodium alkali should be stored in a dry place and sealed packaging;
- soluble in methanol, glycerin, ethanol;
- violently interacts with metals - tin, aluminum hydroxide, lead, zinc, forms hydrogen - an explosive combustible poison;
- absorbs carbon dioxide from the air.
Receipt
Caustic soda is found in brucite mineral. The second largest deposit is concentrated in Russia. Hydroxide, thanks to the research of Nicolas Leblanc, conducted in 1787, is obtained by synthesis from sodium chloride. Later, electrolysis became a popular mining method. Since 1882, scientists have developed a ferritic method for obtaining hydroxide in the laboratory using soda ash. The electrochemical method is now the most popular: sodium ions form its solution of caustic mercury - an amalgam, which dissolves in water.
Application of sodium hydroxide
There is no alkali more common than caustic soda. About 57 million tons are consumed annually. Caustic sodium is used in the production of medicines, phenol, organic dyes, glycerine. Another area of application is the disinfection of a room due to the ability of a chemical compound to neutralize substances harmful to humans in the air. Hydroxides are also widely used to maintain the shape of products (food industry).
In industry
Sodium hydroxide is a strong base for chemical reactions and is actively used by various industries due to its properties:
- Pulp industry - to eliminate sulfate in the composition of wood fibers for softening (delignification). This is necessary in the production of cardboard, paper, artificial fibers.
- Chemical industry - used for the production of oils, neutralization of substances in an acidic environment, in the etching of aluminum, the manufacture of pure metals.
- Sodium hydroxide is used to produce biodiesel fuel based on vegetable oils, as a result of the reaction glycerol is formed.
- The compound is used to wash the molds of automobile tires.
- In civil defense, it is common when neutralizing substances hazardous to health in the air, degassing.
- Used for the illegal production of drugs such as methamphetamines.
Food supplement
Caustic soda peels vegetables and fruits. A substance is used to give the color of caramel. As a food additive E524 (a class of acidity regulators, anti-caking agents along with sodium carbonate) is used in the manufacture of cocoa, ice cream, butter, margarine, chocolate, soft drinks. Olives and black olives soften and turn black.
Food products - bagels and German pretzels (pretzels) - are treated with a caustic solution for a crispy crust. In Scandinavian cuisine there is a fish dish - lutefisk. The preparation technology includes soaking dried cod in a hydroxide solution for 5-6 days until a jelly-like consistency is obtained. In the food industry, soda helps to refine vegetable oil.
In the production of detergents
The ability of the interaction of fats in caustics has been noticed for a long time. Since the 7th century, the Arabs have mastered the production of solid soap with the help of caustic soda and aromatic oils. This technology has remained the same. Caustic soda is added to shampoos, detergents, personal care products. The cosmetic industry uses Na hydroxide to produce anti-grease soaps, nail polish removers, and creams.
At home
The main method of application is gel-like hydroxide or its granules. Included in the means to eliminate blockages of sewerage, heating systems. The dirt dissolves, disaggregates and passes further down the pipe. Stainless steel products cleared of oils using caustic soda heated to 50-60°C with the addition of potassium hydroxide. Cosmetology uses a gel based on it to soften keratinized skin, papillomas, warts.
Sodium hydroxide in medicine
The compound is added to medicines against hyperacidity of the stomach, for a laxative effect of strong action. This remedy leads to increased intestinal peristalsis. The use of the substance restores the acid-base balance. It is used in medicine to achieve a sedative effect, suitable for water purification from impurities. Thanks to sodium chloride, indicators of the osmotic pressure of blood plasma remain constant. Do not confuse it with baking soda, table salt.
The harm of sodium hydroxide
The substance belongs to the second hazard class. Due to the hydroxide's ability to corrode organic compounds, the use of caustic must be carried out with all precautions. If alkali gets on the mucous membranes and skin, it causes severe burns, and interaction with the eyes leads to optic atrophy. To neutralize the hydroxide on the skin, a weak solution of vinegar and a large amount of running water are used.
Video
Sodium hydroxide (food additive E524, caustic soda, sodium hydroxide, caustic soda) is a yellowish or white solid fused mass. According to its chemical properties, sodium hydroxide is a strong alkali.
General properties of sodium hydroxide
Caustic soda is usually available as a clear, colorless solution or as a paste.
Caustic soda is highly soluble in water, releasing heat. When interacting with air, this substance blurs, so it goes on sale in a hermetically sealed container. Under natural conditions, sodium hydroxide is part of the mineral brucite. The boiling point of sodium hydroxide is 1390 °C, the melting point is 322 °C.
Obtaining sodium hydroxide
In 1787, the physician Nicolas Leblanc developed a convenient method for obtaining sodium hydroxide from sodium chloride. Later, the Leblanc method was superseded by the electrolytic method for producing caustic soda. In 1882, a ferritic method for producing sodium hydroxide was developed, based on the use of soda ash.
Currently, sodium hydroxide is most often produced by electrolysis of saline solutions. The ferritic method for producing caustic soda is now rarely used.
Application of sodium hydroxide
Sodium hydroxide is an incredibly popular and widely used chemical compound. About seventy million tons of caustic soda are produced annually.
Caustic soda is used in the pharmaceutical, chemical, food, cosmetic and textile industries. Caustic soda is used in the manufacture of synthetic phenol, glycerin, organic dyes, and drugs. This compound can neutralize airborne components harmful to the human body. Therefore, sodium hydroxide solutions are often used for disinfection of premises.
In the food industry, sodium hydroxide is used as an acidity regulator to prevent clumping and caking. Food additive E524 maintains the necessary consistency of products in the production of margarine, chocolate, ice cream, butter, caramel, jelly, jam.
Bakery products are treated with a solution of caustic soda before baking to obtain a dark brown crispy crust. In addition, the food additive E524 is used for refining vegetable oil.
The harm of sodium hydroxide
Caustic soda is a toxic substance that destroys the mucous membrane and skin. Sodium hydroxide burns heal very slowly, leaving scars. Contact with the eye most often results in loss of vision. If alkali gets on the skin, rinse the affected area with a stream of water. When ingested, caustic soda causes burns of the larynx, oral cavity, stomach and esophagus.
All work with sodium hydroxide should be carried out in goggles and overalls.
DEFINITION
Sodium hydroxide forms hard white, very hygroscopic crystals, melting at 322 o C.
Due to the strong corrosive effect on fabrics, skin, paper and other organic substances, it is called caustic soda. In engineering, sodium hydroxide is often referred to as caustic soda.
In water, sodium hydroxide dissolves with the release of a large amount of heat due to the formation of hydrates.
Sodium hydroxide should be stored in well-closed containers, as it easily absorbs carbon dioxide from the air, gradually turning into sodium carbonate.
Rice. 1. Sodium hydroxide. Appearance.
Obtaining sodium hydroxide
The main method for obtaining sodium hydroxide is the electrolysis of an aqueous solution of sodium chloride. During electrolysis, hydrogen ions are discharged at the cathode and simultaneously sodium ions and hydroxide ions accumulate near the cathode, i.e. sodium hydroxide is obtained; chlorine is released at the anode.
2NaCl + 2H 2 O \u003d H 2 + Cl 2 + 2NaOH.
In addition to the electrolytic method for obtaining sodium hydroxide, sometimes the older method is also used - boiling a solution of soda with slaked lime:
Chemical properties of sodium hydroxide
Sodium hydroxide reacts with acids to form salts and water (neutralization reaction):
NaOH + HCl \u003d NaCl + H 2 O;
2NaOH + H 2 SO 4 \u003d Na 2 SO 4 + H 2 O.
A solution of sodium hydroxide changes the color of indicators, so, for example, when litmus, phenolphthalein or methyl orange are added to a solution of this alkali, their color will turn blue, crimson and yellow, respectively.
Sodium hydroxide reacts with salt solutions (if they contain a metal capable of forming an insoluble base) and acid oxides:
Fe 2 (SO 4) 3 + 6NaOH \u003d 2Fe (OH) 3 ↓ + 3Na 2 SO 4;
2NaOH + CO 2 \u003d Na 2 CO 3 + H 2 O.
Application of sodium hydroxide
Sodium hydroxide is one of the most important products of the basic chemical industry. In large quantities, it is consumed to purify oil refinery products; sodium hydroxide is widely used in soap, paper, textile and other industries, as well as in the production of artificial fibers.
Examples of problem solving
EXAMPLE 1
| Exercise | Calculate the mass of sodium hydroxide that can react with a 300 ml concentrated hydrochloric acid solution (HCl mass fraction 34%, density 1.168 kg/l). |
| Solution | Let's write the reaction equation: NaOH + HCl \u003d NaCl + H 2 O. Let's find the mass of the hydrochloric acid solution, as well as the mass of the dissolved substance HCl in it: m solution = V solution × ρ; m solution \u003d 0.3 × 1.168 \u003d 0.3504 kg \u003d 350.4 g. ω = msolute / msolution × 100%; msolute = ω / 100% ×m solution ; msolute (HCl) = ω (HCl) / 100% ×m solution ; msolute (HCl) = 34 / 100% × 350.4 = 11.91 g. Calculate the number of moles of hydrochloric acid (molar mass is 36.5 g / mol): n(HCl) = m(HCl) / M(HCl); n (HCl) = 11.91 / 36.5 = 0.34 mol. According to the reaction equation n (HCl) :n (NaOH) = 1: 1. Hence, n (NaOH) \u003d n (HCl) \u003d 0.34 mol. Then the mass of sodium hydroxide that has entered into the reaction will be equal to (molar mass - 40 g / mol): m (NaOH) = n (NaOH) × M (NaOH); m (NaOH) \u003d 0.34 × 40 \u003d 13.6 g. |
| Answer | The mass of sodium hydroxide is 13.6 g. |
EXAMPLE 2
| Exercise | Calculate the mass of sodium carbonate that will be required to obtain sodium hydroxide by reaction with calcium hydroxide weighing 3.5 g. |
| Solution | Let us write the reaction equation for the interaction of sodium carbonate with calcium hydroxide to form sodium hydroxide: Na 2 CO 3 + Ca (OH) 2 \u003d CaCO 3 ↓ + 2NaOH. Calculate the amount of calcium hydroxide substance (molar mass - 74 g / mol): n (Ca (OH) 2) \u003d m (Ca (OH) 2) / M (Ca (OH) 2); n (Ca (OH) 2) \u003d 3.5 / 74 \u003d 0.05 mol. According to the reaction equation n (Ca (OH) 2): n (Na 2 CO 3) \u003d 1: 1. Then the number of moles of sodium carbonate will be equal to: n (Na 2 CO 3) \u003d n (Ca (OH) 2) \u003d 0.05 mol. Find the mass of sodium carbonate (molar mass - 106 g / mol): m (Na 2 CO 3) \u003d n (Na 2 CO 3) × M (Na 2 CO 3); m (Na 2 CO 3) \u003d 0.05 × 106 \u003d 5.3 g. |
| Answer | The mass of sodium carbonate is 5.3 g. |
