How to make a cement-sand mortar with your own hands? Solutions of percentage concentration How to make a solution for

Cement mortar today is indispensable in construction. It is used for brick and stone masonry, interior decoration, pouring foundations and plastering. Often, people without building experience have a question - how to make a mortar of cement and sand at home. It is no secret that the consistency and composition of the cement mortar, depending on the purpose of use, will be different. For example, to create a strong foundation, you need to add to the mixture, in addition to and, also heavy crushed stone. The process of preparing the solution is an important and crucial stage, because the strength and durability of the entire structure ultimately depends on its quality.

Varieties of cement mortar

For self-preparation of a cement-sand mixture, it is necessary to initially determine its purpose. Today, classifications are divided into groups of solutions into lean, normal and fatty. Each of them has its own advantages and disadvantages. For example, the proportion of cement in a normal solution does not exceed the norm, while fatty ones contain a lot of cement. Such a building mixture, after setting, quickly cracks. Lean mortars contain more sand than cement, which reduces their strength characteristics. In addition to classification by the amount of cement in the building mixture, there is also such a gradation as the grades of cement and mortar.

cement mortar for various kinds works:

• grades M150 and M200 are usually used for screeding;
• grades M50, M100, M150, M75, M200 and M125 are best suited for masonry;
• grades M10, M50 and M25 - for plastering and interior decoration.

The brand of mortar is an indicator of the strength of the structure erected with its use. The ratio of ingredients depends on the purpose of the cement mortar. In the instructions for ready-made building mixtures, the manufacturer on the packaging indicates information on the preparation, composition and purpose of a particular product. Today it is not difficult to purchase a ready-made mass of the required brand (dry mixes for foundations, plastering and finishing types of work or screeds are quite available, to which you only need to add water). However, significant money savings can be achieved if you do the mixing yourself.

The mortar grades determine its compressive strength after hardening. To prepare cement mortar manually, it is necessary to take into account the types of work. For masonry and plastering, M100 or M150 is usually used.

Stages of creating a cement mortar

The creation of a cement slurry consists of the following processes:

• competent selection of the brand of mixture and cement powder;
• preparation of the remaining ingredients - water, sand and necessary additives;
• direct mixing.

Sometimes in the course of work it is necessary to determine the brand of the resulting solution. To do this, you just need to divide the brand name of dry cement by the number of buckets of sand. For example, when using the main component of brand 400 and four buckets of sand, a solution of brand 100 was obtained. At the first stage, the choice of cement powder is made. The brand will determine the quality of the finished material. The higher its value, the stronger the mixture and, in general, the whole structure will turn out.

Noteworthy is the fact that for one solution it is possible to use different brands cement. The difference lies in the difference in the volume of cement used. Therefore, the higher the grade of dry powder, the less it needs to be added to the mixture. Ideally, if the brand of the mixture matches the brand of the material (this is especially important in the production of plastering and masonry work). In this case, the entire structure will have the same margin of safety.

Methods for preparing cement mixtures

Before you make a cement mortar at home, you need to decide on optimal way production - mechanical or manual. Using the first method involves the use of a concrete mixer. Mixing the solution with your own hands will require specific physical effort, since all the ingredients will need to be mixed in a spacious container with a bayonet shovel. To facilitate efforts, you first need to pour water into the bath or trough, and then add sand with cement. The whole mass will need to be stirred until smooth, add crushed stone and mix everything well again.

A step-by-step video shows the entire kneading process:

A concrete mixer will allow you to knead a mass of a more uniform consistency without much physical effort. First, some water is poured into the concrete mixer. Then liquid is added there. detergent or other additives. For better dissolution, it is necessary to withstand from 3 to 5 minutes, and then add half the sand.

On the next step the entire volume of cement powder is laid. The mixture must be thoroughly mixed, and then pour the rest of the sand. To obtain high-quality liquid cement, you need to accurately calculate the proportion of the main components. The preparation of a grade 100 mortar from M500 cement powder will require a ratio of one part of cement to five parts of sand. In practice, this means that five buckets of sand are needed for one bucket of dry cement powder.

In the case of using cement grade 400, the required ratio will be one to four. The preparation of a mixture of M200 from the same components will require a proportional ratio of parts one to two (if cement 400 is used). Water is added as you mix until the desired consistency is obtained.

Self-preparation of a solution for different types works

To fill the foundation of the building, the sand-cement mass must be maintained in the classical ratio, i.e. one part cement to three parts sand. Crushed stone is also added to it, and in this case concrete is obtained in such a ratio - three parts of crushed stone with sand to one part of Portland cement. Of great importance here is the ratio of the amount of water to other components. A solution in which the amount of water is a quarter of the total volume becomes ideal, but such a mass is difficult to manage. Therefore, during kneading, water in portions until the consistency of thick sour cream is reached.

The optimal ratio of components for plastering and leveling walls is a mixture of two parts of sand with one part of cement.

For a conventional screed, the same ratio of components is used as for creating concrete, only crushed stone replaces screenings here. In terms of composition, this is one part of Portland cement M400 or M500 and two parts each of screenings and sand, respectively. Adding fifty to one hundred grams of liquid detergent to the solution will help improve plasticity. Before mixing, to improve the quality of the solution, all materials must be sieved to avoid the ingress of foreign impurities and to saturate the mixture with oxygen. This will help improve the process of mixing the solution and will promote the chemical interaction of the components of the mixture.

Preparing cement mortar for construction work on your own is an affordable task for any person. It is only necessary to adhere to a clear sequence in the production of work, to take a responsible attitude to the quality and preparation of raw materials.

Any construction is not complete without cement.

Preparation of cement mortar - milestone, since the strength of the structure, the strength of the masonry, and the durability of the structure as a whole directly depend on it.

Before you start mixing, you need to understand how to properly make a cement mortar of the required quality.

Therefore, every self-respecting builder should know how to prepare cement correctly, what grades should be used, what consistency should be, the sequence of mixing elements and proportions. Make accepted from:

• cement;
• sand;
• water;
• additives and plasticizers.

First you need to mix the dry ingredients - cement and sand in a concrete mixer in a ratio of 1: 3.

Depending on the latter, it is customary to distinguish sulfate-resistant, hydrophobic, quick-hardening, plasticized, white or colored, pozzolanic, building and other cements. In addition, the material is produced in different grades, from M100 to M600. The higher the brand, the stronger and stronger the solution will be. However, it is not at all necessary to purchase M200 cement in order to make M200. In construction, the technology of mixing cement and sand is used. Different proportions of the components will help to make different grades of the mixture.

The brand is defined as the brand of cement, which must be divided by the amount of sand. For example, there is cement M400. If you mix a bucket of such material with 4 buckets of sand (proportion 1: 4), then the grade of the prepared solution is determined as 400/4=100 (grade of cement/amount of sand=grade of the mixture). To make a cement composition of the same brand from M500 cement, you will need 5 buckets of sand (500/5 \u003d 100). This formula allows you to correctly determine the initial proportions of the cement mixture for various grades. Now the question arises: what brand of mortar is used in construction? You can answer it correctly only taking into account several factors: brands of building materials and the functional purpose of the mixture.

The use of mixtures

If you add too much water, the cement mortar will turn out to be liquid, respectively, the strength will be lower than that of a thick one.

As a standard, the brand of building materials is equal to the brand of cement mortar. That is, for M100 bricks, a cement composition M100 is required. This combination will allow you to make almost monolithic masonry. But there are also nuances. For example, there is a front masonry made of M350 bricks. The corresponding mortar will simply become a senseless waste of materials and funds, since for facing masonry it is quite enough to make the M115 composition, mix cement and sand in a ratio of 2: 7. Such a mixture, if prepared correctly, is able to provide sufficient resistance to precipitation and wind, which most affect facade structures. At the same time, the M115 solution is quite durable and suitable for seams, you can even drive nails into it.

If the walls have to be made from different blocks, the M100 compound is most suitable for joining. For backfill masonry, when brick M75 is used, it is correct to make mortar M75 (1 bucket of cement is mixed with 5.3 buckets of sand). It is important to observe the proportions as accurately as possible, otherwise the lack of sand is fraught with the rapid drying of the mixture, and the excess - shedding. Water is not excreted in a separate proportion, but is also very important in consistency and characteristics. Depending on its quantity, there are:

Table with cooking instructions

• fatty composition - there is too little water in it, the solution quickly hardens, but after drying it cracks, short-lived;
• normal - all components are mixed correctly, the proportions are observed, it does not freeze quickly, but cracks do not appear in it, very strong and reliable,
• skinny - too much water, this one will not grab.

Water is usually taken in half the volume of cement, but this value is conditional. You need to add water in small portions, gradually, constantly monitoring the consistency of the mixture. The difference between good and bad is only 2% of water. Therefore, it is very important to do everything gradually, without haste and according to technology, because the quality and reliability of the structure directly depends on the cement mortar.

Today, instead of additives and plasticizers, many builders prefer to use conventional detergent. Adding 50-100 g makes the composition more plastic and easy to use. So, having decided on the brand of the mixture, components and proportions, it's time to proceed to the most important thing - preparing the solution.

Preparation of the cement composition

Mobility device

You can make the mixture both manually and in a concrete mixer. The second method is much more convenient, faster and more efficient, especially when it comes to large volumes. It is extremely important to thoroughly mix the components in order to achieve complete homogeneity, with a stirrer it is much easier to do this. The classic recipe involves pouring water into the machine (about half the mixture), if necessary, it is added later. Detergent is added to the water. Then cement and sand are poured into the mixer. There should be enough water to ensure that the solution is evenly mixed. It seems most convenient to first make it thinner so that it mixes well, gradually adding components to it. Proportions must be strictly observed.

Please note that the detergent should be completely dissolved in water and form a foam, evenly distributed throughout the mixture. Sand and cement are best mixed in liquid state, therefore, it seems most reasonable to pour detergent, cement, half the sand and about the same amount of water into the mixer, adjusting the density at the end of the batch. Water with detergent is mixed for 3-5 minutes, until a homogeneous foamy mass is formed. Half of the sand and all of the cement are mixed for another 1-3 minutes. Add the remaining sand, adjust the water. The last batch lasts another 3-5 minutes. As practice shows, builders can pour components into the mixer in a different order, in principle of great importance has no order. The main thing is that the mixture is homogeneous, without lumps, seals and air bubbles.

Cement in bags varies by type and each of them is labeled.

When mixing by hand, sand and cement come first, they are mixed in a dry state. When the mixture becomes even gray color, the whole mass is raked into one bed, at the top of which a recess is made. Water is added to it in small portions, the mixture is scooped up from the edges and kneaded. The operation is repeated several times until the solution reaches the desired consistency. It is best to mix the composition on a board or iron sheet, but not on the ground, so that foreign components do not get into the mixture. A high-quality cement composition resembles sour cream in consistency, not liquid, but not thick either. The trace on the surface of such a mixture from a hand or a shovel remains clear, not blurry.

Cement mortars are divided into the following categories:

• for laying bricks, arranging floor screeds, plastering walls and other construction work;
• for pouring concrete foundations.

Each type of cement causes a different strength and is designated by a specific brand.

The classic "recipe" for building mixtures includes cement, sand and water. An additional component is introduced into the composition of mixtures for foundations - crushed stone.

How to make a solution? To do this, you need to use only high-quality components, as well as mix them in strictly defined proportions. This is all the more important if the owner intends to build a house on his own, without resorting to the services of specialists.

Main characteristics of cement

These include:

• frost resistance;
• sulfate resistance;
• water resistance;
• fineness of grinding;
• strength.

Frost resistance is responsible for the ability of a material to endure repeated freeze-thaw cycles without consequences. It is determined by the brand of cement and increased by introducing special additives - mylonaphth (sodium naphthenate) and SSB - sulfite-alcohol stillage (residual product obtained by evaporating liquor). These substances are introduced in small quantities into the solution at the stage of its preparation: PRS concentrates - 0.15-0.2% of the total volume of dry matter, soap naphtha - 0.05-0.1%.

Sulfate resistance ensures that the material is resistant to the constant corrosive effects of sea water rich in sulfate ions. Waterproof cement is used for sealing joints in concrete structures that are in the water. The fineness of grinding determines the setting time of the mixture, and also positively affects its strength. However, too fine grinding can provoke excessive water absorption, thereby significantly reducing the quality of concrete.

The grades of cement that are best suited for most construction work and the production of concrete mixtures are M 400 and M 500. Marking means that this type of material can withstand loads of up to 400 and 500 kg per cm², respectively. These Construction Materials differ in optimum indicators of frost resistance, water resistance and durability.

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What else you need to know about the components

It is better to purchase cement right before pouring the foundation or other construction work from trusted manufacturers. It is preferable to buy it in bags, not loose. You can determine the quality by scooping a little and sifting through your fingers. Poor-quality stale cement will form lumps. It should be stored exclusively in a dry room with good ventilation, however, it should be remembered that even under ideal storage conditions, it loses about a third of its strength in a year.

The sand must be clean, sifted by hand or mechanically sieved and free of clay. River or quarry sand is used (ideally quartz sand). Another important component is added to the cement mortar for pouring foundations - crushed stone of medium fractions with grain sizes of 25-40 mm. The gravel should also be washed well before use. To increase the strength of the foundations, gravel or granite screenings are added to the cement mortar: they take 2 parts of the screening instead of 1 part of sand and 1 part of crushed stone.

The water used to prepare the cement mortar must be absolutely clean, without foreign impurities and oils. Cooled water is used in summer and heated water in winter. In the case of preparing foundation mixtures, the water consumption per 1 m³ of concrete is approximately 125 liters. Add water with great care, as the cement will absorb as much water as it needs - no more and no less. Excess moisture will remain in the finished concrete, forming voids and cavities, turning into ice in winter and thereby reducing the strength of the foundation.

To obtain a cement mortar of the highest quality, plasticizers are used that increase the mobility and elasticity of mixtures. Waterproofers are used to create waterproof concrete screeds, plastering and masonry mixtures. Additional reinforcing additives are placed in the foundation mixtures - reinforcing polypropylene fiber. To color the solution, organic and mineral pigments are used - special powder dyes. They are mainly used for painting the masonry joints of stoves and fireplaces.

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Proportions of foundation, masonry and building mixtures

For pouring the foundations of private residential buildings, concrete M 300 and M 400 are used. The ratio of the various components that are needed to make the mortar is determined by the brand of cement:

• for concrete M 300: 1 hour of cement M 400, 1.9 hours of sand, 3.7 hours of crushed stone;
• for concrete M 400: 1 hour of cement M 400, 1.2 hours of sand, 2.7 hours of crushed stone;
• for concrete M 300: 1 hour of cement M 500, 2.4 hours of sand, 4.3 crushed stone;
• for concrete M 400: 1 hour of cement M 500, 1.6 hours of sand, 3.2 crushed stone.

As in the case of foundation mortars, the ratio of components in masonry and building mixtures determined by the brand of cement:

• for mortar M 100: 1 hour of cement M 400, 4 hours of sand;
• for mortar M 100: 1 hour of cement M 500, 5 hours of sand;
• for mortar M 200: 1 hour of cement M 400, 2 hours of sand;
• for mortar M 200: 1 hour of cement M 500, 3 hours of sand.

Lime is introduced into the compositions for plastering. Such solutions are used for finishing rooms with high humidity. The proportions of the ingredients are:

• 1 hour of cement M 400, 3 hours of sand, 0.1 hours of lime.

For laying tiles in order to better adhere to the surface, "lean" solutions are used, which are characterized by a high content of sand. Here the proportions will be as follows: for cement M 400, 4 parts of sand are taken, for M 500 - 6 parts.

Solutions are homogeneous systems formed by two or a large number components. The component whose content in the solution predominates is usually called the solvent; the component with the lower content is called the solute.

Methods for expressing the concentration of solutions

The quantitative content of a solution component, related to a certain mass or to a certain volume of a solution or solvent, is called the concentration of this component. The solute content is usually expressed in units of mass, in moles or in equivalents.

Percent concentration (by mass) is the number of mass units of a solute contained in 100 mass units of a solution. (Below, the percentage concentration is denoted C%.) Thus, 20% water solution KOH contains 20 mass units of KOH and 80 mass units of water.

Molar concentration (molarity) is expressed as the number of moles of a solute in 1 liter of solution and is denoted by the letter M or Cm.

A mole is a unit of quantity of a substance. A mole is the amount of matter in a system that contains that many molecules, atoms, ions, electrons, or other structural units how many atoms are contained in 0.012 kg of the carbon isotope 12C (6.022 * 10 in 23). The mass of a substance contained in 1 mole of a given simple or complex substance is called the molar mass. The molar mass of a substance, expressed in grams per mole, has the same numerical value as its relative molecular mass.

The number of moles of a simple or complex substance n is found from the ratio of the mass m of this substance in the system under consideration to its molar mass M:

The product of the volume of the solution, expressed in milliliters, and its molarity is equal to the number of millimoles of the solute.

Equivalent concentration (normality) is expressed as the number of equivalents of a solute in 1 liter of solution and is denoted by the letters N, n. or sn.

The equivalent of a substance is such a quantity of it that in this reaction is equivalent (equivalent) to 1 mole of hydrogen atoms (1.0079 g). The mass of 1 equivalent is called the equivalent mass.

Expressing the concentration of solutions in units of normality greatly simplifies the calculation of the volumes of solutions of substances that quantitatively react with each other. These volumes are inversely proportional to their concentrations expressed in units of normality:

The product of the volume of the solution, expressed in milliliters, and its normality is equal to the number of milliequivalents of the solute.

The concentration of solutions is also expressed through the titer, i.e., by the mass (in g or mg) of the substance contained in 1 ml of the solution, and is denoted by the letter T. The value found is called the titer of the dissolved (working) substance. In analytical practice, the titer of the analyte is also used, i.e., the mass (in g or mg) of the analyte, equivalent to the amount of the reagent contained in 1 ml of the solution.

For example, the titer of 0.1 N H2SO4 (equivalent mass of H2SO4 = 49.04 g/mol) is:

When titrated with this NaOH solution, the titer of H2SO4, expressed in terms of the analyte NaOH (equivalent mass of NaOH = 40.01 g/mol) is:

The concentration of solutions is often expressed in units of molality - the number of moles of a substance dissolved in 1 kg of solvent. Molality is denoted by the letter m.

Formulas for the transition from some expressions of the concentration of solutions to others

We accept the following conventions for concentration:

C% - percentage concentration by weight;
A is the number of mass units of the solute per 100 mass units of the solvent;
B is the mass of the dissolved substance in 1 liter of solution;
Сн is the number of equivalents of a solute in 1 liter of solution (normality);
Cm is the number of moles of a solute in 1 liter of solution (molarity);
m is the number of moles of a solute per 1000 g of solvent (molality);
E is the equivalent mass of the solute, g/mol;
M is the molar mass of the solute, g/mol;
d - relative density.

Solubility

Solubility is a value that characterizes the ability of a substance to form a homogeneous system with a given solvent. Quantitatively, the solubility of a gas, liquid, or solid in a liquid solvent is measured by the concentration of a saturated solution at a given temperature.

Usually, the solubility of solid and liquid substances is expressed by the solubility coefficient, i.e., the mass of a substance that dissolves under given conditions in 100 mass units of the solvent to form a saturated solution. (A saturated solution is one that is in equilibrium with an excess of the solute.)

Each temperature corresponds to a certain solubility of a given substance in a given solvent. Information about solubility is given in reference books.

The solubility of gases in liquids increases with increasing pressure and, in most cases, with decreasing temperature.

The solubility of liquid substances in liquids can be unlimited when the liquid components are mixed with each other in any ratio (ethyl alcohol - water) and limited in the case of immiscible liquids. In the latter case, the separation of the liquid components of the system depends on the temperature; usually the mutual solubility of the components increases with temperature. Above a certain temperature point, called the critical solubility point, the mutual solubility of the components of the system becomes unlimited (there is no separation).

The solubility of solids in liquids can vary widely. It usually increases with temperature. However, some substances do not obey this rule: their solubility either decreases with increasing temperature, or increases only to a certain limit, above which the solubility decreases.

Solution preparation technique

According to the accuracy of expressing the concentration, solutions are divided into approximate, exact and empirical.

Solutions of acids and bases of approximate concentration serve as auxiliary reagents in the performance of analytical, preparative and other works. The concentration of such solutions is calculated either by the degree of dilution of the initial substances (solutions), or by the mass of the substance (weighed on a technical scale) dissolved in a known mass of the solvent. Often the approximate concentration of solutions is determined by the value of the density.

Solutions with precise, predetermined concentrations, called working, standard, or titrated solutions, serve to determine the exact concentration of other solutions.

The concentrations of many solutions of excipients (indicators, specific reagents, etc.) are established empirically and are given in the relevant prescriptions.

Regardless of the concentration accuracy of the solutions, only pure starting materials and water of a high degree of purification should be used, and in some cases (for NaOH, Na2S2O3 solutions) - purified from CO2.

It should be borne in mind that the rate of dissolution of a solid depends on the size of its particles (finely divided dissolves faster).

Some substances are not wetted by water and float on its surface, forming a thin film. To prepare aqueous solutions of such substances, it is recommended to pour the powder first with a small amount of ethyl alcohol (if it is inert with respect to the components of the solution), and only then add water.

Vessels for dissolving and storing base solutions should be equipped with calcium chloride tubes filled with ascarite or soda lime to protect the solution from CO2. In some cases, solutions should be stored under an inert gas atmosphere (N2, CO2). Solutions of substances that decompose under the action of light, such as AgNO3, should be stored in vessels made of brown glass or covered with black lacquer (in extreme cases, wrapped in black paper).

Preparation of aqueous solutions of acids of approximate concentration

Aqueous solutions of acids (H2SO4, HCl, HNO3) are usually prepared by appropriate dilution of the initial chemically pure concentrated acids. Dilution is carried out on a volume basis, since a liquid is always easier to measure than to weigh. To obtain a dilute acid (for example, 1:5), 1 volume of acid is added to 5 volumes of water.

The percentage of concentrated acids is controlled by density, determined for the most part hydrometer. For acid concentration values ​​depending on density, see reference books.

Concentrated acids should be handled with care, as they have a strong effect on the skin, destroy clothes and shoes, spoil floors and tables. Wear rubber gloves and goggles when working with concentrated acids.

When preparing dilute solutions of acids (especially H2SO4), the acid should be poured into water in a thin stream with continuous stirring with a glass rod. If at the same time the mixture is very hot, then it is cooled, after which the next portion of the acid is added.

Acid that has come into contact with shoes or clothing must be immediately washed off with a large volume of water, neutralized with ammonia or NaHCO3 and rinsed again with water. The acid spilled on the table or on the floor is covered with sand, neutralized with Na2CO3, CaO, Ca(OH)2, CaCO3, and only after that they are cleaned.

When preparing dilute solutions from more concentrated ones or by mixing solutions of different concentrations, it is convenient to use the so-called cross or mixing rule to calculate the volume ratio. This rule can be illustrated by a scheme for obtaining a 5% (by mass) solution by diluting a 20% solution:

The rule of the cross also applies to the case when the concentration of mixed aqueous solutions is expressed in terms of density. Let an aqueous solution with a density of 1.57 g/cm3 be given. It is necessary to prepare a solution from it with a density of 1.20 g / cm3. According to the rule of the cross, we draw up a diagram:

hence it follows that 20 cm3 of a solution with p = 1.57 g/cm3 must be mixed with 37 parts by mass of water.

The calculation of the concentration according to the rule of the cross is not accurate, and this method can only be used to prepare solutions of approximate concentration.

Preparation of anhydrous perchloric acid solution

A solution of perchloric acid in anhydrous acetic acid is widely used as a titrant for acid-base titrations in non-aqueous media.

The industry produces perchloric acid of various concentrations (from 42 to 70%), most often in the form of a 57% aqueous solution with a density of about 1.50.

Excess water from perchloric acid is removed with acetic anhydride:

Having previously determined the water content in perchloric acid, the latter is dissolved in glacial acetic acid and it is calculated what volume V1 (in ml) of acetic anhydride is necessary to remove excess water from perchloric acid:

where 100 - A - water content in the initial solution of HClO4,%; V is the volume of HClO4 taken to prepare the solution, ml; p is the density of the applied HClO4 solution, g/cm3; p1 - ​​density of acetic anhydride, g/cm3; 102 - molecular weight of acetic anhydride; 18 - molecular weight of water.

A certain volume of HClO4 V is gradually, with continuous stirring, poured into 800 ml of glacial acetic acid, V1 ml of acetic anhydride is added, mixed thoroughly, the volume of the solution is adjusted to 1 liter with glacial acetic acid and mixed again. A day later, the solution is ready.

Preparation of alkali solutions

When dissolving NaOH or KOH, rubber gloves and goggles should be used. Alkalis cause chemical burns to the skin, destroy clothes and shoes. It is forbidden to take solid alkali with your hands.

Aqueous solutions of NaOH and KOH. When solid NaOH and KOH are dissolved in water, strong heating occurs; therefore, saturated solutions of alkalis are prepared in heat-resistant glass or, better, in porcelain dishes, gradually adding solid alkali with stirring to avoid local overheating.

In air, NaOH and KOH absorb water and CO2. The resulting carbonates are slightly soluble in a concentrated solution of alkalis and gradually precipitate out.

Concentrated alkali solutions, when stored in glassware, destroy glass, leaching silicic acid out of it. Therefore, it is better to store them in polyethylene vessels.

From concentrated solutions, dilute alkali solutions are obtained, the concentration of which is controlled by density. The approximate value of the volumes of the dilute solution of alkali and water can also be calculated according to the rule of the cross.

Preparation of a 50% NaOH solution that does not contain carbonates (according to GOST 4517-75) is carried out as follows: 250 g of NaOH in 250 ml of distilled water are dissolved in a porcelain glass with gradual addition and stirring. After cooling, the solution is poured into a polyethylene vessel, closed with a cork and kept for 2-3 weeks, until NaCO3 is completely precipitated. The clear solution is then siphoned with a glass tube and diluted accordingly with CO2-free water.

Alcoholic solution of KOH. The solubility of NaOH and KOH in methanol is higher than in ethyl alcohol. However, since methyl alcohol is highly toxic and flammable, ethanolic solutions of NaOH and KOH are commonly used. The solubility of NaOH in ethyl alcohol at 28 °C is 14.7%, and KOH is 27.9%.

To prepare a KOH solution, rectified ethyl alcohol, previously purified from aldehydes, is used.

The most effective purification method is the following: a solution of 2 g of AgNO3 in 5 ml of distilled water is poured into 1200 ml of ethyl alcohol in a flask with a ground stopper and mixed thoroughly. Separately, 5 g of KOH are dissolved in 25 ml of hot ethyl alcohol, the solution is cooled and poured into alcohol solution AgNO3. A precipitate of Ag2O is formed, which is allowed to settle, filtered, and the alcohol is distilled off. Ethanol, purified in this way, remains colorless for several years.

During storage, an alcoholic solution of KOH often acquires a slightly yellow color due to the resinification of impurities. For the preparation of KOH solutions that do not stain during long-term storage, it is recommended to pre-treat alcohol with aluminum butylate (5 g per 1 liter of alcohol). Mixtures are allowed to stand for 3-4 weeks at room temperature, after which the alcohol is decanted and KOH is dissolved in it.

Preparation of an aqueous solution of ammonia

A commercially available aqueous ammonia solution with a density of 0.901-0.907 g/cm3 at 20°C contains 25-27% NH3. The drug and its dilute solutions are quite suitable for most preparative and auxiliary laboratory work.

Gaseous ammonia causes eye and nasal irritation, nausea and headaches. All work with ammonia must be carried out in a fume hood.

From bottled ammonia. Assemble the installation (Fig. 63). Ammonia bottle 1 is installed and fixed on stand 2. The bottle is connected to an empty intermediate bottle 3, to which two absorption bottles 4 with NaOH solution are attached to absorb CO2. Ammonia, purified from CO2, enters the receiver 5, where there is twice distilled distilled water that does not contain CO2. Saturation with ammonia is carried out until the density of the solution in the receiver reaches 0.907 g/cm3, which corresponds to a 25% ammonia solution.

To obtain a more concentrated solution, the receiver is cooled with ice water in bath 8.

Flask 6 - splash catcher; bottle 7 containing the NaOH solution prevents CO2 from entering the receiver from the air.

from aqueous ammonia. 500 ml of aqueous ammonia are placed in a 1-liter round-bottom flask and a freshly prepared slurry of 10 g of CaO and water is carefully added.

The flask is connected to a vertical reflux condenser, the upper end of which is closed with a tube of soda lime, and the solution is left alone for 18-20 hours. Then the installation is assembled (Fig. 64). Flask 2 with aqueous ammonia is placed on water bath 1 so that the refrigerator is directed upward at an angle of 45 °, and its upper end is connected through an intermediate flask 4 with a receiver - a flask 5 containing 300-400 ml of water, and a closed tube with soda lime 6. When heating aqueous ammonia in a water bath gaseous ammonia enters the receiver and is completely absorbed by the water. Saturation with ammonia is carried out until the density of the solution in the receiver reaches 0.907 g/cm3, which corresponds to a 25% ammonia solution.

Preparation of working solutions of exact concentration

Preparation of a solution from a sample of a standard substance. Taken with an accuracy of 0.0002 g, a weighed portion of the dried standard substance, which approximately corresponds to the given concentration calculated to obtain a certain volume of solution, is carefully transferred into a volumetric flask and dissolved in a small volume of distilled water that does not contain CO2. The resulting solution, with periodic shaking, is diluted with water, bringing the volume of the solution in a volumetric flask slightly below the mark. Then the flask with the solution is kept for 15-20 min at 20°C and water is carefully added up to the mark. The flask is stoppered and the contents are shaken for 15-30 minutes.

Knowing the mass of the starting substance and the volume of the solution, calculate its concentration.

To simplify subsequent calculations, it is convenient to use the normality correction (or normality coefficient) K. This correction is the ratio of the normality of the prepared solution to the given normality of the solution, expressed as integers, tenths, or hundredths of normality. For example, the normality of the prepared solution turned out to be 0.1036 N., and the specified one was 0.1 N. In this case

By multiplying the volume of the solution used for titration by this correction K, an equivalent volume of a given concentration is obtained (in this case, 0.1 N).

In table. Table 3 lists some solid standard substances with which the concentration of the most commonly used working solutions can be accurately determined.

Preparation of solutions from fixanals. Fixanals, or standard titers, are precisely weighed amounts of a reagent or its solution sealed in a glass ampoule. As a rule, each ampoule contains 0.1 equivalent of the substance. With the quantitative transfer of the contents of such an ampoule into a 1-liter volumetric flask and bringing the volume of the solution with water to the mark at 20 ° C, exactly 0.1 N is obtained. solutions.

Fixcanals are available HCl, H2SO4, NaOH, KOH, Na2CO3, NaCl, Na2C2O4, H2C2O4-2H2O, K2Cr2O7, K2C2O4, Na2S2O3-5H2O, KMnO4, AgNO3, NH4SCN, KSCN, NaSCN, BaCl2-2H2O, (NH4)2C2O4-H2O, Na2B4O7 -10H2O, KCl, K2CO3, NH4Cl, I2, etc.

at first warm water wash off the inscription on the ampoule and wipe it well with a clean towel. A funnel with a glass striker embedded in it (usually attached to each box of fixanal) is inserted into a volumetric flask with a capacity of 1 liter, the sharp end of which should be turned upwards (Fig. 65). The ampoule with fixanal is allowed to fall freely so that the thin bottom of the ampoule breaks when it hits the sharp end of the striker. After that, the side recess of the ampoule is pierced with another glass striker and the contents are allowed to flow out. Without changing the position of the ampoule, the end of the rinsing tube drawn into the capillary and bent upwards is inserted into the formed upper hole, and the ampoule is washed from the inside with a strong jet. Then, the outer surface of the ampoule and the funnel with a striker are well washed with a jet of water from the washer. After removing the ampoule from the funnel, bring the liquid level in the flask to the mark. Close the flask tightly and mix the solution thoroughly.

When using fixanal 0.1 n. iodine before opening the ampoule must be placed in a volumetric flask 30-40 g KI for complete dissolution of iodine.

Ampoules with fixanals of solids (H2C2O4-2H2O, NaCl, KMnO4, etc.) are opened in the same way as described above, but the funnel must be completely dry. When the ampoule is broken, its contents are poured into the flask by gentle shaking, the ampoule and funnel are thoroughly washed with distilled water.

Fixanal AgNO3 darkens after 2-3 years under normal storage conditions. Fixanals of most other solids and acids can be stored indefinitely.

Fixanals NaOH, KOH are only suitable for 6 months from the date of issue. Turbidity of alkaline solutions is a sign of their deterioration.

Accurate concentration working solutions should be as freshly prepared as possible. The exception is KMnO4 solutions, the titer of which should be set no earlier than 3-4 days after their preparation.

When storing working solutions, their concentration should be checked periodically. Working solutions of alkalis and sodium thiosulfate should be protected from CO2 (calcium chloride tubes with soda lime or ascarite).

Vessels containing working solutions should be clearly labeled with substance, normality, correction factor, date of manufacture and date of concentration testing.

The GOST standards prescribe the proportions of cement mortars used for various purposes.

The proportions of the concrete mixture largely depend on the brand, the fillers and additives used, as well as on the type of structure and its location.

In the preparation of a cement mortar for the installation of large-block structures, masonry and other types of work, the ratio of components should be strictly observed.

Varieties of cement mortars:

• masonry,
• plastering,
• facing.

For interlayers and seams, the compositions M150, M300 and M400 are used, for coatings - M200, M300, for screeds it is best to take M150 and M200.

The strength of the masonry and the strength of the structure, as well as the durability of the task as a whole, depend on how well the cement mortar is prepared.

If necessary, the solution may contain additives or be without them, have a thick or liquid consistency.

Cement mortar is produced from the following components:

• cement,
• water,
• sand,
• plasticizers and additives (depending on the requirements for the composition).

With the help of additives, it is possible to obtain quick-hardening, sulfate-resistant, hydrophobic, plasticized, pozzolanic, colored, white and other types of cement mortar. In their production, cement of different grades is used - M100-M600. However, this does not mean at all that in order to obtain a mixture of M400, it is necessary to use cement of the same brand.

In the production of concrete mixtures, the technology of mixing the base material, as well as sand and water in certain proportions, is used.

For example, from cement M400 by adding 4 buckets of sand in a ratio of 1: 4, we will get a brand of mortar M100. To prepare a mortar M100 from M500 cement, instead of 4 buckets of sand, you need to add 5 buckets.

Cement-lime mortar correct proportions

Consider how to prepare a mixture for the construction of ground objects, provided that the relative humidity inside the house is not more than 60%, or for foundations erected on soils containing no a large number of moisture.

With a brand of concrete mortar M10 and cement M150, a proportion of 1: 1.2: 9.5 will be applied (respectively - cement: lime: sand), for mortar M50 and cement M200 - proportions 1: 0.3: 4, subject to the use of cement M400 - 1: 0.9: 8. Obtaining a mixture of M100 (M500) the ratio of components is 1: 0.5,: 5.5, for M150 (from M400) the proportions are 1: 0.2: 3 and for the M200 solution (from M400 cement) - the proportions will be 1: 0 ,1:2.5.

Mortars used in ground structures where relative humidity exceeds 60%, as well as in the construction of foundations on wet soils, will be made taking into account the following proportions:

• M10 from M150 cement - 1: 1: 9, for a mixture of M50 (from M300) the ratio of components is 1: 0.6: 6, for M 100 from M400 - proportions 1: 0.4: 4.5, preparation of a solution of M150 (from cement M500) - 1: 0.3: 4 and for a mixture of M300 (from M400) the proportions will be 1: 0.7: 1.8.

We mix the cement-sand mortar with our own hands

When erecting foundations and other structures below the groundwater level or on soils saturated with moisture, the cement mortar is produced in compliance with the following proportions:

• the brand of mortar M100 from cement M400 and building sand will have proportions - 1: 4.5, for a mixture of M150 (M400) - 1: 3, for a mixture of M300 from M500, the proportions - 1: 2.1.

In more detail, the ratio of the elements of cement mortars is prescribed in tables SP 82-101-98.

It is important to keep the proportions exactly. A lack of sand can lead to a quick solidification of the mixture, and its excess can lead to sprinkling. Water also has a great influence on the characteristics and consistency of the mix.

Depending on the water content in the cement mortar, they are divided into:

• fatty - there is little water in the mixture, so it quickly hardens and cracks after drying;
• skinny - too much water. Such a mixture may not seize;
• normal - when mixing the components, all proportions are observed as accurately as possible. Such a mixture does not harden quickly and after hardening the concrete does not crack, but has the required strength and reliability.

You can introduce water into the mixture in small portions. It is worth remembering that the difference between low-quality and good concrete mortar is all in 2% of water.

Instead of plasticizers and mineral additives many builders prefer regular detergent. It provides the mixture with plasticity and makes it more convenient to use.

However, too much detergent can lead to foaming, the solution will become like cotton wool and lose its properties. For one batch, add 50-100 g.

How to prepare a cement mortar

You can mix the components manually or in a concrete mixer. The second option is much faster, more convenient and more efficient. If you plan to prepare concrete solutions in large quantities, you cannot do without a concrete mixer.

We fill clean water, add detergent and start pouring cement and sand (half of the required amount). After the mixture has become homogeneous, add the remaining sand and stir for 3-5 minutes. The result should be a cement mortar without lumps and air bubbles.

If the components are mixed manually, then initially dry cement and sand should be mixed in a separate container, then a funnel is created in it and water is started to be poured in small portions. Stir the mixture to the consistency of sour cream. A clear trace of a shovel should be visible on the surface of the finished solution.