How to prepare a cement mortar for the foundation. Methods for preparing mortars How to make a cement mortar with your own hands

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Until now, no construction or repair is complete without the use of cement. Deciding how to cook cement mortar, you must first consider that used for brickwork, floor screed or finishing walls and ceilings can differ significantly both in composition and in the method of preparation.

In the manufacture of a concrete mixture, cement serves as an astringent that ensures its solidification.

The main components of cement mortar

There are two types of mortar - cement and concrete. Despite the similarity in the components (in addition to the three common components, crushed stone or gravel is additionally added to concrete) and the method of preparation, these are two completely different products designed to solve different construction problems.

A classic cement mortar consists of only three components mixed together in a certain proportion: cement, sand and water. The cement must be dry and free from hard lumps. It is best to use river sand, although in practice they often take ordinary, quarry sand, but they pre-screen it to separate debris and impurities.

To mix the mixture, it is better to use clean water at room temperature or slightly warmer - 21-23 ° C.

The optimal proportions are: 1 part cement to 3 parts sand. Water is added to the prepared cement mortar as needed, its amount can vary from 80 to 95% of the volume of cement used (i.e., 8 to 9.5 liters of water should be consumed per 10 liters of cement).

With such a solution, you can both expel brickwork and perform plastering work. However, it has a number of disadvantages - excessive rigidity and limited time (1-1.5 hours) for using the prepared solution, which makes it difficult to work with it.

Therefore, professional builders prefer to add various substances to its composition when preparing a cement mortar, making it more plastic and extending its hardening time by 2-3 times. The most common way to improve such a mixture is to add milk of lime to its composition.

Such a mixture has almost the same binding abilities as a pure cement mortar, but its use time increases to 3-4 hours.

The second option is to prepare a cement solution with the addition of a small amount of detergent - at the rate of 50-100 g for every 10 liters of the mixture (depending on the quality of the detergent).

This additive can significantly increase its plasticity.

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Mortar grades and their use

Like the vast majority building materials, the prepared cement mortar also has its own marking. There are solutions M10, M25, M50, M75, M100, M125, M150, M200, M250, M300, but in private construction grades from M75 to M150 are usually used.

The marking of the finished mortar does not depend directly on the brand of cement used for its preparation, as most non-professionals mistakenly believe. In fact, a mixture of one brand can be prepared from different brands cement.

For example, a mixture of M100 can be obtained from cement M300, M400, M500, and in all cases the amount of cement used for its preparation will be the same. But the amount of sand changes: when using cement M300, the ratio of sand and cement will be 3:1; when using M400 - 4: 1; and when using the M500 - 5: 1.

When using cement mortar, professional builders advise using the composition of the same brand as the material used for construction. Those. if a concrete mortar M75 is used to pour the foundation, then a cement mixture of the same brand must be used to screed the basement. If brick M100 is used to extrude walls, then the mixture for masonry must correspond to this brand.

But in practice this is not always possible. For example, using an M300 brick when distilling walls, it makes no sense to take a solution of the same brand for laying it - it is difficult to work with such a solution, and the financial costs for its manufacture are very large. Quite suitable for the operation of the brand in the range from M100 to M150. In practice, such masonry is most often performed using a mixture of sand and cement M400 in a ratio of 3.5: 1, i.e. approximately M115.

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How to make a cement mortar

There are several ways to prepare a quality cement mixture. But, regardless of the method chosen, tools will be needed for its preparation:

• container for mixing components;
• shovel;
• trowel;
• buckets.

The most common classical method of preparing a mixture is that cement and sand are first mixed dry until a homogeneous composition is obtained, and then this mixture is diluted to the desired consistency with water. Water should not be added all at once, but 80-85% of the required amount, and already in the process of preparing the mixture, gradually add it to the composition, achieving the desired density.

Especially this rule should be observed if not a pure cement-sand mixture is being prepared, but a cement-lime mixture. In this case, you first need to prepare liquid lime by diluting the lime dough with water to a state of thin sour cream. Then the solution is prepared in the same way as in the first variant, but instead of the missing water, final stage milk of lime is added to it.

The second method was invented by craftsmen for preparing the solution by hand. In fact, it is almost a mirror image of the first: first, water is poured into the container (approximately 4/5 of the required amount), then liquid soap or other detergent. After that, the water must be vigorously shaken for 4-5 minutes so that the detergent is completely dissolved in it and forms the maximum amount of foam.

Then half of the required volume of sand and the entire volume of cement are poured into the container. After that, all components are mixed with each other. Special care in mixing at this stage is not yet required, the main thing is that as a result the mixture is more or less homogeneous in composition. Then the missing sand is added to the mixture, and here negligence in mixing is already unacceptable - you need to knead until the mixture becomes homogeneous. The presence in it of areas of clean, without cement, sand is unacceptable.

The main advantage of this method is that in the liquid state sand and cement are mixed much faster and better than in the dry state. But in order to properly make a cement mortar, at the end of preparation, you need to gradually add the missing water, bringing the solution to the desired density.

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Little tricks when preparing the solution

Despite the apparent simplicity of the process, even experienced builders are not always able to immediately prepare the cement mortar correctly. Therefore, the prepared solution is divided into 3 types:

• skinny;
• normal;
• fatty.

To determine the type of prepared mixture, no special tools are needed. It is enough to pull out the shovel used for mixing from it or (in the case of a concrete mixer) slightly stir the finished mixture with a trowel. If the working surface of the tool remains almost clean, then the prepared mixture is lean, because it lacks a binder - cement. If the entire surface of the tool is hidden under a layer of the prepared mixture, then there is too much cement in the latter, it is greasy.

Only a normal solution is suitable for work, in which the proportions of cement, sand and water are correctly maintained. If the solution turned out to be lean, then cement should be poured into it, and if it is greasy, add sand and water, bringing it to a normal state. It is necessary to add the components little by little, otherwise it costs nothing to turn a lean solution into a greasy one and vice versa.

Initially, water should always be poured a little less than the norm.

The fact is that its amount depends on the absorbency of sand - dry sand absorbs water much more than wet sand. Therefore, pouring it according to the norm and filling it with slightly damp sand, you risk getting a liquid solution.

Cement mortars are divided into the following categories:

• for laying bricks, arranging floor screeds, plastering walls and other construction works;
• 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 used for grouting concrete structures located 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.

Cement grades optimally suited for most construction and manufacturing applications concrete mixtures, - M 400 and M 500. Marking means that this type of material is able to withstand loads up to 400 and 500 kg per cm², respectively. These building materials are distinguished by optimal indicators of frost resistance, water resistance and strength.

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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, plaster 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 is 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.

Cement-sand mortar is the basis for both the foundation and the laying of walls. Very often, due to poor-quality mortar, the building begins to collapse in a matter of years under the influence of deformations. Now we will talk about how to properly make a mortar for the foundation with our own hands, as well as consider the requirements for the components of the mortar.

Requirements for the components of the cement-sand mortar

The main components of the cement-sand mortar are water, cement (binder) and sand (aggregate). Also, depending on various conditions, in which the cement-sand mortar is made, it is recommended to add all kinds of hardeners and other auxiliary additives. In order for the solution to be durable and of high quality, the first step is to choose its main components correctly.

First, water. It should be clean, tap water will do. The water should be free of oil and acid impurities, construction debris and other pollutants.

As for sand, special requirements are also imposed on it. Sand should not be mixed with clay or other rocks. It is best to use river sand.

Cement must be selected based on the purpose of the solution. If in the future it will serve for pouring the foundation, then it is recommended to choose cement not lower than the M300, or even M400 grade. Cement in paper bags does not have a bad reputation, which is why it is recommended to use it. A very important requirement for cement is to buy it 1-2 weeks before the start of construction, because. with long periods of storage, it begins to harden and becomes unusable. If you still buy cement for a long time before the start of construction, it must be carefully wrapped in plastic wrap to prevent the influence of moist air on the material.

If you decide to make not a cement-sand, but a concrete mortar with your own hands, then you need to add another important component to it - crushed stone. The purpose of crushed stone is another mortar filler, which will not only significantly save cement consumption, but also make the mortar more durable. The following requirement is imposed on crushed stone - particle sizes should not be too small, but not too large. The most ideal option is particles with a diameter of 2.5 - 3.5 cm.

For example, in order to make the solution more elastic, a detergent of a not very high price is added.

Also one of the popular additives in the cement-sand mortar for masonry walls are dyes. Their purpose is to make the seam darker or lighter, at the request of the owner of the building. Soot is used as the simplest additive, but you need to be careful with it, because. its excessive amount reduces the strength of the cement slurry.

We have provided you with the most important requirements for the components of the cement-sand mortar, now let's move on to what proportions of the cement-sand mortar are most suitable.

The most suitable proportions of cement-sand mortar

In order for the cement-sand mortar to be durable, it is necessary to choose and calculate its proportions correctly. For laying walls, it is necessary to create a brand of cement mortar M100. To do this, you can take cement brand M400 and make the proportion of cement with sand 1: 4. To create other brands of mortar, we use the same method, for example, to get a cement-sand mortar of the M200 brand, we mix 2 buckets of sand and 1 bucket of M400 cement.

It should be noted that the creation of a strong solution (M300 - M350) is not always appropriate, because. this entails an increased consumption of cement (and hence higher material costs), and also does not provide an order of magnitude higher strength.

We also draw your attention to the fact that the most successful proportion for country construction work is the ratio of cement and sand 1:3.

For rough masonry walls, it is allowed to add clay to the mortar, which will give elasticity to the mortar and reduce the cost of building materials.

How to make a cement-sand mortar with your own hands?

First of all, you need to choose the option of mixing the solution - with a concrete mixer or manually, we will analyze both options.

It is clear that mixing the mortar with a concrete mixer will significantly save both health and strength and, of course, construction time. The only problem is that the construction itself requires a lot of material costs and there is not always money left to buy an inexpensive but useful concrete mixer. In this case, we have already provided an article on how to easily and quickly make a functional .

So, back to the process of mixing with a concrete mixer. First of all, we fill in water, not too much, but not too little, approximately 60-70% of the total amount of water needed.
Next, add about 100 grams of detergent to the water and wait until it is thoroughly mixed with water (about 2 minutes).

After that, add half the amount of sand and all the cement necessary for the solution. The solution should also be thoroughly mixed, if necessary, a little water is added to it.

As soon as the solution becomes homogeneous, add the remaining amount of sand to it and wait until everything is completely mixed.

Water must be added so much that the result would be the consistency of liquid sour cream.

It should be noted that a solution that is too thick will be inconvenient to use, in fact, as well as too rare. Moreover, in the latter case, the solution will lose its strength properties.

Now let's move on to the option of mixing the cement-sand mortar manually. To do this, first prepare a container where we will mix (a trough will do).

Next, pour all the dry mass (cement and sand) into the trough and mix thoroughly until a homogeneous consistency. After that, water is added to the mixture (little by little) and mixed until a creamy consistency is formed.

A very important point is that the cement-sand mortar sets quickly, so if you work alone, then mix no more than 30 liters of mortar.

It should also be noted that in winter time the water needs to be slightly heated so that the solution does not set so quickly, otherwise the water will freeze, and the strength of the foundation or masonry will noticeably decrease.

In summer, on the contrary, you must use cold water(like from a faucet). If it is too hot, the poured solution must be soaked several times a day by hand, otherwise the foundation will crack.

This, in fact, is all that I wanted to talk about how to make a cement-sand mortar with your own hands. We hope that the article was useful to you, and we wish you good luck in creating country houses.

building with your own hands!

Any construction is not complete without cement.

The preparation of cement mortar is an important stage, 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 original proportions cement mixture for various brands. 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. Best of all, sand and cement are mixed in a liquid state, so 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 mix 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, the order does not matter in principle. 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.

Solutions

Preparation of salt solutions

Technique for determining the concentration of solutions.

Determination of concentration by densimetry

Determination of concentration titrimetrically.

Basic concepts and terms of titrimetric analysis.

Scheme of titrimetric determination.

Six rules of titration.

Conditions for titrimetric determination of the concentration of a substance

Preparation of a titrated solution according to the exact weight of the starting substance

Setting the titer of the solution using the adjusting agent

Computations in volumetric analysis.

List of used literature

SOLUTIONS

1. The concept of solutions and solubility

In both qualitative and quantitative analysis, the main work is done with solutions. Usually, using the name "solution", we mean true solutions. In true solutions, the solute in the form of individual molecules or ions is distributed among the solvent molecules.

Solution- a homogeneous (homogeneous) mixture consisting of particles of a dissolved substance, a solvent, and the products of their interaction. When a solid is dissolved in water or another solvent, the molecules of the surface layer pass into the solvent and, as a result of diffusion, are distributed throughout the volume of the solvent, then a new layer of molecules passes into the solvent, etc. Simultaneously with the solvent, the reverse process occurs - the release of molecules from the solution. The higher the concentration of the solution, the more this process will occur. By increasing the concentration of the solution, without changing other conditions, we reach a state in which per unit time the same number of molecules of the solute will be released from the solution as it will dissolve. Such a solution is called saturated. If you add even a small amount of a solute to it, it will remain undissolved.

Solubility- the ability of a substance to form homogeneous systems with other substances - solutions in which the substance is in the form of individual atoms, ions, molecules or particles. The amount of a substance in a saturated solution determines solubility substances under these conditions. Solubility various substances different in different solvents. In a certain amount of each solvent, no more than a certain amount of a given substance can be dissolved. Solubility expressed as the number of grams of a substance in 100 g of solvent in a saturated solution, at a given temperature . According to the ability to dissolve in water, substances are divided into: 1) highly soluble (caustic soda, sugar); 2) sparingly soluble (gypsum, Bertolet's salt); 3) practically insoluble (copper sulfite). Substances that are practically insoluble are often referred to as insoluble, although there are no absolutely insoluble substances. “Insoluble substances are usually called those whose solubility is extremely low (1 part by weight of the substance dissolves in 10,000 parts of the solvent).

Generally, the solubility of solids increases with increasing temperature. If a solution close to saturated is prepared by heating, and then quickly but carefully cooled, a so-called supersaturated solution. If a crystal of a solute is thrown into such a solution or mixed, then crystals will begin to fall out of the solution. Therefore, a cooled solution of a substance contains more than is possible for a saturated solution at a given temperature. Therefore, when a crystal of a solute is introduced, the entire excess of the substance crystallizes out.

The properties of solutions are always different from the properties of the solvent. The solution boils at high temperature than a pure solvent. The freezing point, on the contrary, is lower for the solution than for the solvent.

According to the nature of the solvent, solutions are divided into aquatic and non-aqueous. The latter include solutions of substances in such organic solvents as alcohol, acetone, benzene, chloroform, etc.

Solutions of most salts, acids, alkalis are prepared in water.

2. Methods for expressing the concentration of solutions. The concept of gram equivalent.

Each solution is characterized by the concentration of a solute: the amount of a substance contained in a certain amount of solution. The concentration of solutions can be expressed as a percentage, in moles per 1 liter of solution, in equivalents per 1 liter of solution and in titer.

The concentration of substances in solutions can be expressed in different ways.

The mass fraction of the solute w(B) is a dimensionless value equal to the ratio of the mass of the solute to the total mass of the solution m

or otherwise called: percentage concentration solution - is determined by the number of grams of a substance in 100 g of a solution. For example, a 5% solution contains 5 g of substance in 100 g of solution, i.e. 5 g of substance and 100-5 = 95 g of solvent.

The molar concentration C(B) shows how many moles of a solute are contained in 1 liter of solution.

C(B) = n(B) / V = ​​m(B) / (M(B) V),

where M(B) - molar mass solute g/mol.

Molar concentration is measured in mol/l and is denoted by "M". For example, 2 M NaOH is a two molar solution of sodium hydroxide; one-molar (1 M) solutions contain 1 mol of a substance in 1 liter of solution, two-molar (2 M) - 2 moles in 1 liter, etc.

In order to establish how many grams of a given substance is in 1 liter of a solution of a given molar concentration, it is necessary to know its molar mass, i.e., the mass of 1 mole. The molar mass of a substance, expressed in grams, is numerically equal to the molecular weight of the substance. For example, the molecular weight of NaCl is 58.45, therefore, the molar mass is also 58.45 g. Thus, 1 M NaCl solution contains 58.45 g of sodium chloride in 1 liter of solution.

The normality of a solution refers to the number of gram equivalents of a given substance in one liter of solution or the number of milligram equivalents in one milliliter of solution.
Gram - equivalent substance is the number of grams of a substance numerically equal to its equivalent.

Complex substance equivalent- call such an amount that in this reaction corresponds (equivalently) to 1 mole of hydrogen.

The equivalence factor is defined:

1) the nature of matter,

2) a specific chemical reaction.

a) in exchange reactions;

The equivalent value of acids is determined by the number of hydrogen atoms that can be replaced in an acid molecule by metal atoms.

Example 1 Determine the equivalent for acids: a) Hcl, b) H 2 SO 4, c) H 3 RO 4; d) H 4 .

Solution.

In the case of polybasic acids, the equivalent depends on the particular reaction:

a) H 2 SO 4 + 2KOH → K 2 SO 4 + 2H 2 O.

in this reaction, two hydrogen atoms are replaced in the sulfuric acid molecule, therefore, E \u003d M.M / 2

b) H 2 SO 4 + KOH → KHSO 4 + H 2 O.

In this case, one hydrogen atom is replaced in the sulfuric acid molecule E \u003d M.M / 1

For phosphoric acid, depending on the reaction, the values ​​a) E \u003d M.M / 1

b) E= M.M/2 c) E= M.M/3

GROUNDS

The base equivalent is determined by the number of hydroxyl groups that can be replaced by an acid residue.

Example 2 Determine the equivalent of the bases: a) KOH; b) Cu(OH) 2 ;

Solution.

Salt equivalent values ​​are determined by cation.

The value by which M.M should be divided in the case of salts is q n, where q is the charge of the metal cation, n is the number of cations in the salt formula.

Example 3 Determine the equivalent of salts: a) KNO 3 ; b) Na 3 PO 4; c) Cr 2 (SO 4) 3;

Solution.

a) q n = 1 b) 1 3 = 3 in) z = 3 2 = 6, G) z = 3 1 = 3

The value of the equivalence factors for salts also depends on

reactions, similar to its dependence for acids and bases.

b) in redox reactions for determining

equivalent use the electronic balance scheme.

The value by which M.M should be divided for a substance in this case is equal to the number of electrons received or given away by a substance molecule.

K 2 Cr 2 O 7 + HCl → CrCl 3 + Cl 2 + KCl + H 2 O

for a straight line 2Cr +6 +2 3 e→2Cr3+

reactions 2Cl - - 2 1 e→Cl2

for the reverse 2Cr+3-2 3 e→Cr+6

Cl2-2 reactions e→2Cl

(K 2 Cr 2 O 7) \u003d 1/6

(Cr)=1/3 (HCl)=1 (Cl)=1) (Cl2)=1/2 (Cl)=1

Normal concentration is indicated by the letter N (in calculation formulas) or the letter "n" - when designating the concentration of a given solution. If 1 liter of a solution contains 0.1 equivalent of a substance, it is called decinormal and is denoted as 0.1 n. A solution containing 0.01 equivalents of a substance in 1 liter of solution is called a centinormal solution and is designated 0.01 N. Since the equivalent is the amount of any substance that is in this reaction. corresponds to 1 mole of hydrogen, obviously, the equivalent of any substance in this reaction must correspond to the equivalent of any other substance. And this means that in any reaction, substances react in equivalent quantities.

Titrated called solutions whose concentration is expressed titer, i.e., the number of grams of a substance dissolved in 1 ml of a solution. Very often, in analytical laboratories, the titers of a solution are recalculated directly for the analyte. Tog Yes the titer of the solution shows how many grams of the analyte corresponds to 1 ml of this solution.

To prepare solutions of molar and normal concentrations, a sample of the substance is weighed on an analytical balance, and the solutions are prepared in a volumetric flask. When preparing acid solutions, the required volume of a concentrated acid solution is measured with a burette with a glass tap.

The weight of the solute is counted to the fourth decimal place, and the molecular weights are taken with the accuracy with which they are given in the reference tables. The volume of concentrated acid is calculated to the second decimal place.

When preparing solutions of percentage concentration, the substance is weighed on techno-chemical scales, and liquids are measured with a graduated cylinder. Therefore, the weight of the substance is calculated with an accuracy of 0.1 g, and the volume of 1 liquid with an accuracy of 1 ml.

Before proceeding with the preparation of the solution, it is necessary to make a calculation, i.e., calculate the amount of solute and solvent to prepare a certain amount of a solution of a given concentration.

3. Calculations in the preparation of salt solutions

Example 1. It is necessary to prepare 500 g of a 5% solution of potassium nitrate. 100 g of such a solution contains 5 g of KN0 3 ; We make a proportion:

100 g solution-5 g KN0 3

500" - X» KN0 3

5*500/100 = 25 g.

Water should be taken 500-25 = 475 ml.

Example 2. It is necessary to prepare 500 g of a 5% CaCl solution from the CaCl 2 .6H 2 0 salt. First, we calculate for an anhydrous salt.

100 g solution-5 g CaCl 2

500 » » - x r CaCl 2

5*500/ 100 = 25 g

The molar mass of CaCl 2 \u003d 111, the molar mass of CaC1 2 6H 2 0 \u003d 219. Therefore,

219 g of CaCl 2 *6H 2 0 contain 111 g of CaCl 2 . We make a proportion:

219 g CaC1 2 * 6H 2 0 - 111 g CaC1 2

X"CaCl 2 -6H 2 0-25" CaCI 2,

219 * 25 / 111 \u003d 49.3 g.

The amount of water is 500-49.3=450.7 g, or 450.7 ml. Since water is measured with a graduated cylinder, tenths of a milliliter are not taken into account. Therefore, you need to measure 451 ml of water.

4. Calculations in the preparation of acid solutions

When preparing acid solutions, it must be taken into account that concentrated acid solutions are not 100% and contain water. In addition, the required amount of acid is not weighed, but measured with a graduated cylinder.

Example 1. It is necessary to prepare 500 g of a 10% hydrochloric acid solution, based on the available 58% acid, the density of which is d=l,19.

1. Find the amount of pure hydrogen chloride that should be in the prepared acid solution:

100 g solution -10 g HC1

500 » » - X» HC1

500*10/100= 50g

To calculate solutions of percentage concentration, the molar mass is rounded to whole numbers.

2. Find the number of grams of concentrated acid, which will contain 50 g of HC1:

100 g acid-38 g HC1

X» » - 50 » NS1

100 50/38 = 131.6g.

3. Find the volume that this amount of acid occupies:

V = 131,6/ 1.19= 110.6 ml. (round up to 111)

4. The amount of solvent (water) is 500-131.6 = 368.4 g, or 368.4 ml. Since the required amount of water and acid is measured with a graduated cylinder, tenths of a milliliter are not taken into account. Therefore, to prepare 500 g of a 10% hydrochloric acid solution, it is necessary to take 111 ml of hydrochloric acid and 368 ml of water.

Example 2. Usually, in calculations for the preparation of acids, standard tables are used, which indicate the percentage of an acid solution, the density of a given solution at certain temperature and the number of grams of this acid contained in 1 liter of a solution of a given concentration. In this case, the calculation is simplified. The amount of prepared acid solution can be calculated for a certain volume.

For example, you need to prepare 500 ml of a 10% hydrochloric acid solution, based on a concentrated 38% solution. According to the tables, we find that a 10% hydrochloric acid solution contains 104.7 g of HC1 in 1 liter of solution. We need to prepare 500 ml, therefore, the solution should be 104.7: 2 = 52.35 g H C1.

Calculate how much concentrated acid should be taken. According to the table, 1 liter of concentrated HC1 contains 451.6 g of HC1. We make a proportion:

1000 ml - 451.6 g HC1

X ml- 52.35 "HC1

1000 * 52.35 / 451.6 \u003d 115.9 ml.

The amount of water is 500-116 = 384 ml.

Therefore, to prepare 500 ml of a 10% solution of hydrochloric acid, you need to take 116 ml of a concentrated solution of HC1 and 384 ml of water.

Example 1. How many grams of barium chloride is needed to prepare 2 liters of a 0.2 M solution?

Solution. The molecular weight of barium chloride is 208.27. Consequently. 1 liter of 0.2 M solution should contain 208.27 * 0.2 = = 41.654 g of BaCI 2. To prepare 2 liters, 41.654 * 2 \u003d 83.308 g of BaCI 2 will be required.

Example 2. How many grams of anhydrous soda Na 2 C0 3 will be required to prepare 500 ml of 0.1 n. solution?

Solution. The molecular weight of soda is 106.004; equivalent mass of Na 2 C0 3 \u003d M: 2 \u003d 53.002; 0.1 eq. = 5.3002 g.

1000 ml 0.1 n. solution contain 5.3002 g of Na 2 C0 3
500 »» » » » X » Na 2 C0 3

x \u003d 2.6501 g Na 2 C0 3.

Example 3 How much concentrated sulfuric acid (96%: d=1.84) is required to prepare 2 liters of 0.05N. sulfuric acid solution?

Solution. The molecular weight of sulfuric acid is 98.08. Equivalent mass of sulfuric acid H 2 so 4 \u003d M: 2 \u003d 98.08: 2 \u003d 49.04 g. Weight 0.05 equiv. \u003d 49.04 * 0.05 \u003d 2.452 g.

Let's find how much H 2 S0 4 should be contained in 2 l 0.05 n. solution:

1 l-2.452 g H 2 S0 4

2"- X » H 2 S0 4

X\u003d 2.452 * 2 \u003d 4.904 g H 2 S0 4.

To determine how much you need to take a 96% solution of H 2 S0 4 for this, we make up the proportion:

in 100 g conc. H 2 S0 4 -96 g H 2 S0 4

At» » H 2 S0 4 -4.904 g H 2 S0 4

Y \u003d 5.11 g H 2 S0 4.

We recalculate this amount by volume: 5.11: 1.84 = 2.77

Thus, to prepare 2 liters of 0.05 N. solution should take 2.77 ml of concentrated sulfuric acid.

Example 4 Calculate the titer of a NaOH solution if its exact concentration is known to be 0.0520 N.

Solution. Recall that the titer is the content in 1 ml of a solution of a substance in grams. Equivalent mass of NaOH=40. 01 g Find how many grams of NaOH are contained in 1 liter of this solution:

40.01 * 0.0520 \u003d 2.0805 g.

1 liter of solution contains 1000 ml.

T=0.00208 g/ml. You can also use the formula:

T=E N/1000 g/l

where T- titer, g/ml; E- equivalent weight; N- the normality of the solution.

Then the titer of this solution: 40.01 0.0520/1000=0.00208 g/ml.

Example 5 Calculate the normal concentration of a solution of HN0 3 if it is known that the titer of this solution is 0.0065. To calculate, we use the formula:

T=E N/1000 g/l, from here:

N=T1000/E0,0065.1000/ 63.05= 0.1030 n.

Example 6. What is the normal concentration of a solution if it is known that 200 ml of this solution contains 2.6501 g of Na 2 C0 3

Solution. As calculated in Example 2: ENa 2 co 3 =53.002.
Let's find how many equivalents are 2.6501 g of Na 2 C0 3:
2.6501: 53.002 = 0.05 equiv.

In order to calculate the normal concentration of the solution, we compose the proportion:

1000 » » X "

1 liter of this solution will contain 0.25 equivalents, i.e. the solution will be 0.25 n.

For this calculation, you can use the formula:

N \u003d P 1000 / E V

where R - amount of substance in grams; E - equivalent mass of the substance; V is the volume of the solution in milliliters.

ENa 2 co 3 \u003d 53.002, then the normal concentration of this solution

2,6501* 1000 / 53,002*200=0,25

5.Recalculation of concentration from one type to another.

In laboratory practice, it is often necessary to recalculate the concentration of available solutions from one unit to another. When converting a percentage concentration to a molar one and vice versa, it must be remembered that the percentage concentration is calculated for a certain mass of the solution, and the molar and normal concentrations are calculated for the volume, therefore, for conversion, it is necessary to know the density of the solution.

The density of the solution is given in the reference books in the relevant tables or measured with a hydrometer. If we denote: FROM- percentage concentration; M- molar concentration; N - normal concentration; d- density of the solution; E- equivalent weight; m- molar mass, then the formulas for converting from percentage concentration to molar and normal will be as follows:

Example 1. What is the molar and normal concentration of a 12% sulfuric acid solution, the density of which is d=l.08 g/cm??

Solution. The molar mass of sulfuric acid is 98. Therefore,

E n 2 so 4 \u003d 98: 2 \u003d 49.

Substituting the necessary values ​​into the formulas, we get:

1) the molar concentration of a 12% sulfuric acid solution is

M=12*1.08*10/98=1.32 M;

2) the normal concentration of a 12% sulfuric acid solution is

N= 12 * 1.08 * 10 / 49 \u003d 2.64 n.

Example 2. What is the percentage concentration of 1 N. hydrochloric acid solution, the density of which is 1.013?

Solution. The molar mass of HCl is 36.5, therefore Ens1= 36.5. From the above formula (2) we get:

therefore, the percentage concentration of 1 n. hydrochloric acid solution is

36,5*1/ 1,013*10 =3,6%

Sometimes in laboratory practice it is necessary to recalculate the molar concentration to normal and vice versa. If the equivalent mass of a substance is equal to the molar mass (for example, KOH), then the normal concentration is equal to the molar concentration. So, 1 n. hydrochloric acid solution will be simultaneously 1 M solution. However, for most compounds, the equivalent mass is not equal to the molar and, therefore, the normal concentration of solutions of these substances is not equal to the molar concentration. To convert from one concentration to another, we can use the formulas:

M \u003d (NE) / m; N=M(m/E)

Example 3. Normal concentration of 1M sulfuric acid solution Answer-2M

Example 4 Molar concentration 0.5N Na 2 CO 3 solution Answer-0.25N

When converting a percentage concentration to a molar one and vice versa, it must be remembered that the percentage concentration is calculated for a certain mass of the solution, and the molar and normal concentrations are calculated for the volume, therefore, for conversion, it is necessary to know the density of the solution. If we denote: c - percentage concentration; M is the molar concentration; N - normal concentration; e - equivalent mass, r - density of the solution; m is the molar mass, then the formulas for converting from percentage concentration will be as follows:

M = (c p 10) / m
N = (c p 10) / e

The same formulas can be used if you need to convert the normal or molar concentration to a percentage.

Sometimes in laboratory practice it is necessary to recalculate the molar concentration to normal and vice versa. If the equivalent mass of a substance is equal to the molar mass (For example, for HCl, KCl, KOH), then the normal concentration is equal to the molar concentration. So, 1 n. hydrochloric acid solution will be simultaneously 1 M solution. However, for most compounds, the equivalent mass is not equal to the molar and, therefore, the normal concentration of solutions of these substances is not equal to the molar concentration.
To convert from one concentration to another, you can use the formulas:

M = (N Oe) / m
N = (M m) / Oe

Law of mixing solutions

The amounts of mixed solutions are inversely proportional to the absolute differences between their concentrations and the concentration of the resulting solution.

The law of mixing can be expressed by the mathematical formula:

mA / mB \u003d C-b / a-c,

where mA,mB are the amounts of solutions A and B taken for mixing;

a, b, c, respectively, the concentration of solutions A and B and the solution obtained as a result of mixing. If the concentration is expressed in%, then the amount of mixed solutions must be taken in weight units; if the concentrations are taken in moles or normals, then the amounts of mixed solutions must be expressed only in liters.

For ease of use mixing rules apply rule of the cross:

m1 / m2 = (w3 - w2) / (w1 - w3)

To do this, subtract the smaller one diagonally from the larger concentration value, get (w 1 - w 3), w 1 > w 3 and (w 3 - w 2), w 3 > w 2. Then make up the mass ratio of the initial solutions m 1 / m 2 and calculate.

Example
Determine the masses of the initial solutions with a mass fraction of sodium hydroxide of 5% and 40% if, when they are mixed, a solution of 210 g with a mass fraction of sodium hydroxide of 10% is formed.

5 / 30 \u003d m 1 / (210 - m 1)
1/6 \u003d m 1 / (210 - m 1)
210 - m 1 \u003d 6m 1
7m 1 = 210
m 1 =30 g; m 2 \u003d 210 - m 1 \u003d 210 - 30 \u003d 180 g

Basic concepts and terms of titrimetric analysis.

Titrant - reagent solution of known concentration (standard solution).

Standard solution- according to the method of preparation, primary secondary standard solutions are distinguished. Primary is prepared by dissolving a precise amount of a pure chemical in a specific amount of solvent. The secondary is prepared with an approximate concentration and its concentration is determined according to the primary standard.

Equivalence point– the moment when the added volume of the working solution contains an amount of a substance equivalent to the amount of the substance to be determined.

Purpose of titration- accurate measurement of the volumes of two solutions containing an equivalent amount of a substance

direct titration- this is the titration of a certain substance "A" directly with titrant "B". It is used if the reaction between "A" and "B" proceeds quickly.

Solutions

The concept of solutions and solubility

Methods for expressing the concentration of solutions. The concept of gram equivalent.

Calculations in the preparation of solutions of salts and acids

Recalculation of concentration from one type to another.

Mixing and dilution of solutions. The law of mixing solutions

Solution preparation technique.

Preparation of salt solutions

Preparation of acid solutions

Preparation of base solutions

Preparation of working solution from fixanal.