How to prepare a solution of hydrochloric acid. Means of protection

For safety and ease of use, it is recommended to buy the acid as diluted as possible, but sometimes you have to dilute it even more at home. Don't forget about protective equipment for the body and face, since concentrated acids cause severe chemical burns. To calculate required amount acid and water, you will need to know the molarity (M) of the acid and the molarity of the solution you need to obtain.

Steps

How to calculate the formula

Explore what you already have. Look for the acid concentration designation on the packaging or in the task description. This value is usually indicated as molarity, or molar concentration (M for short). For example, 6M acid contains 6 moles of acid molecules per liter. Let's call this initial concentration C 1.

• The formula will also use the value V 1. This is the volume of acid we will add to the water. We likely won't need the entire bottle of acid, although we don't know the exact amount yet.

1. Decide what the result should be. The required concentration and volume of acid are usually indicated in the text of the chemistry problem. For example, we need to dilute the acid to 2M, and we will need 0.5 liters of water. Let us denote the required concentration as C 2, and the required volume is as V 2.

   • If you are given other units, first convert them to molarity units (moles per liter) and liters.
   • If you don't know what concentration or volume of acid is needed, ask a teacher or someone knowledgeable about chemistry.

2. Write a formula to calculate the concentration. Each time you dilute an acid, you will use the following formula: C 1 V 1 = C 2 V 2. This means that the original concentration of a solution multiplied by its volume equals the concentration of the diluted solution multiplied by its volume. We know that this is true because the concentration times the volume equals the total amount of acid, and the total amount of acid will remain the same.

   • Using the data from the example, we write this formula as (6M)(V 1)=(2M)(0.5L).

3. Solve equation V 1. The V 1 value will tell us how much concentrated acid we need to get the desired concentration and volume. Let's rewrite the formula as V 1 =(C 2 V 2)/(C 1), then substitute the known numbers.

   • In our example, we get V 1 =((2M)(0.5L))/(6M). This equals approximately 167 milliliters.

4. Calculate the required amount of water. Knowing V 1, that is, the available volume of acid, and V 2, that is, the amount of solution that you will get, you can easily calculate how much water you will need. V 2 - V 1 = required volume of water.

   • In our case, we want to get 0.167 liters of acid per 0.5 liter of water. We need 0.5 liters - 0.167 liters = 0.333 liters, that is, 333 milliliters.

5. Wear safety glasses, gloves and a gown. You will need special glasses that will cover the sides of your eyes as well. To avoid burning your skin or burning through your clothing, wear gloves and a robe or apron.

   Work in a well-ventilated area. If possible, work under a switched-on hood - this will prevent acid vapors from harming you and surrounding objects. If you don't have a hood, open all windows and doors or turn on a fan.

6. Find out where the source of running water is. If the acid gets into your eyes or skin, you will need to rinse the affected area under cool water. running water 15-20 minutes. Don't start working until you know where the nearest sink is.

   • When rinsing your eyes, keep them open. Look up, down, to the sides so that your eyes are washed from all sides.

7. Know what to do if you spill acid. You can buy a special kit for collecting spilled acid, which will include everything you need, or purchase neutralizers and absorbents separately. The process described below is applicable to hydrochloric, sulfuric, nitric and phosphoric acids. Other acids may require different handling.

   • Ventilate the room by opening windows and doors and turning on the hood and fan.
   • Apply A little sodium carbonate (soda), sodium bicarbonate, or calcium carbonate onto the outer edges of the puddle, ensuring that the acid does not splash.
   • Gradually pour the entire puddle towards the center until you cover it entirely with the neutralizing substance.
   • Mix thoroughly plastic stick. Check the pH value of the puddle with litmus paper. Add more neutralizing agent if the reading is greater than 6-8, then rinse the area with plenty of water.

How to dilute acid

1. Cool the water with luda. This should only be done if you will be working with high concentration acids, for example, 18M sulfuric acid or 12M hydrochloric acid. Pour water into a container and place the container on ice for at least 20 minutes.

   • Most often, water at room temperature is sufficient.

2. Pour distilled water into a large flask. For applications requiring extreme precision (such as titrimetric analysis), use a volumetric flask. For all other purposes, a regular conical flask will do. The container must fit the entire required volume of liquid, and there must also be room so that the liquid does not spill.

   • If the capacity of the container is known, there is no need to accurately measure the amount of water.

3. Add a small amount of acid. If you are working with a small amount of water, use a graduated or measuring pipette with a rubber tip. If the volume is large, insert a funnel into the flask and carefully pour the acid in small portions with a pipette.

   • Do not use pipettes in the chemistry laboratory that require air to be drawn in through the mouth.

Description of the substance

Properties of hydrochloric acid

Hydrogen chloride solution is chemically harmful, its hazard class is second.

Salt liquid is a strong monobasic acid that can react with a variety of metals, their salts, oxides and hydroxides, it can react with silver nitrate, ammonia, calcium hypochlorite and strong oxidizing agents:

Physical properties and effects on the body

At high concentrations, it is a caustic substance that can cause burns not only to the mucous membranes, but also skin. It can be neutralized with a solution baking soda. When opening containers with concentrated saline solution, its vapors, in contact with moisture in the air, form a condensate of toxic vapors in the form of tiny droplets (aerosol), which irritates the respiratory tract and eyes.

The concentrated substance has a characteristic pungent odor. Technical grades of hydrogen chloride solution are divided into:

red, unrefined, its color is mainly determined by impurities of ferric chloride;

purified, colorless liquid in which the concentration of HCl is about 25%;

fuming, concentrated, liquid with a HCl concentration of 35-38%.

Chemical properties

How do you get it?

The process of producing salt liquid consists of the stages of obtaining hydrogen chloride and absorbing it with water.

Exists three industrial methods producing hydrogen chloride:

synthetic

sulfate

from by-product gases (exhaust gases) of a number technological processes. The last method is the most common. By-product HCl is usually formed during dehychlorination and chlorination organic compounds, manufacturing potash fertilizers, pyrolysis of metal chlorides or organic waste containing chlorine.

Storage and transportation

Industrial hydrochloric acid is stored and transported in specialized polymer-coated tanks and containers, polyethylene barrels, glass bottles packed in boxes. Hatches of containers and tanks, caps of barrels and bottles must ensure the tightness of the container. The acid solution should not come into contact with metals located in the voltage line to the left of hydrogen, as this can cause explosive mixtures.

Application

in metallurgy for extracting ores, removing rust, scale, dirt and oxides, soldering and tinning;

in the production of synthetic rubbers and resins;

in galvanoplasty;

as an acidity regulator in Food Industry;

for the production of metal chlorides;

to produce chlorine;

in medicine for the treatment of insufficient acidity of gastric juice;

as a cleaning and disinfectant.

Approximate solutions. In most cases, the laboratory has to use hydrochloric, sulfuric and nitric acids. Acids are commercially available in the form of concentrated solutions, the percentage of which is determined by their density.

Acids used in the laboratory are technical and pure. Technical acids contain impurities and therefore are not used in analytical work.

Concentrated hydrochloric acid smokes in air, so you need to work with it in a fume hood. The most concentrated hydrochloric acid has a density of 1.2 g/cm3 and contains 39.11% hydrogen chloride.

The dilution of the acid is carried out according to the calculation described above.

Example. You need to prepare 1 liter of a 5% solution of hydrochloric acid, using a solution with a density of 1.19 g/cm3. From the reference book we find out that a 5% solution has a density of 1.024 g/cm3; therefore, 1 liter of it will weigh 1.024 * 1000 = 1024 g. This amount should contain pure hydrogen chloride:

An acid with a density of 1.19 g/cm3 contains 37.23% HCl (we also find it from the reference book). To find out how much of this acid should be taken, make up the proportion:

or 137.5/1.19 = 115.5 acid with a density of 1.19 g/cm3. Having measured out 116 ml of acid solution, bring its volume to 1 liter.

Sulfuric acid is also diluted. When diluting it, remember that you need to add acid to water, and not vice versa. When diluted, strong heating occurs, and if you add water to the acid, it may splash, which is dangerous, since sulfuric acid causes severe burns. If acid gets on clothes or shoes, you should quickly wash the doused area with plenty of water, and then neutralize the acid with sodium carbonate or ammonia solution. In case of contact with the skin of your hands or face, immediately wash the area with plenty of water.

Particular care is required when handling oleum, which is a sulfuric acid monohydrate saturated with sulfuric anhydride SO3. According to the content of the latter, oleum comes in several concentrations.

It should be remembered that with slight cooling, oleum crystallizes and is in a liquid state only at room temperature. In air, it smokes, releasing SO3, which forms sulfuric acid vapor when interacting with air moisture.

It is very difficult to transfer oleum from large to small containers. This operation should be carried out either under draft or in air, but where the resulting sulfuric acid and SO3 cannot have any harmful effect on people and surrounding objects.

If the oleum has hardened, it should first be heated by placing the container with it in warm room. When the oleum melts and turns into an oily liquid, it must be taken out into the air and there poured into smaller dishes, using the method of squeezing with air (dry) or inert gas(nitrogen).

When nitric acid is mixed with water, heating also occurs (though not as strong as in the case of sulfuric acid), and therefore precautions must be taken when working with it.

In laboratory practice, solids are used organic acids. Handling them is much simpler and more convenient than liquid ones. In this case, care should only be taken to ensure that the acids are not contaminated with anything foreign. If necessary, solid organic acids are purified by recrystallization (see Chapter 15 “Crystallization”),

Precise solutions. Precise acid solutions They are prepared in the same way as approximate ones, with the only difference that at first they strive to obtain a solution of a slightly higher concentration, so that later it can be diluted precisely, according to calculations. For precise solutions, use only chemically pure preparations.

The required amount of concentrated acids is usually taken by volume calculated based on density.

Example. You need to prepare 0.1 and. H2SO4 solution. This means that 1 liter of solution should contain:

An acid with a density of 1.84 g/cmg contains 95.6% H2SO4 n to prepare 1 liter of 0.1 n. of the solution you need to take the following amount (x) of it (in g):

The corresponding volume of acid will be:

Having measured exactly 2.8 ml of acid from the burette, dilute it to 1 liter in a volumetric flask and then titrate with an alkali solution to establish the normality of the resulting solution. If the solution turns out to be more concentrated), the calculated amount of water is added to it from a burette. For example, during titration it was found that 1 ml of 6.1 N. H2SO4 solution contains not 0.0049 g of H2SO4, but 0.0051 g. To calculate the amount of water needed to prepare exactly 0.1 N. solution, make up the proportion:

Calculation shows that this volume is 1041 ml; the solution needs to be added 1041 - 1000 = 41 ml of water. You should also take into account the amount of solution taken for titration. Let 20 ml be taken, which is 20/1000 = 0.02 of the available volume. Therefore, you need to add not 41 ml of water, but less: 41 - (41*0.02) = = 41 -0.8 = 40.2 ml.

* To measure the acid, use a thoroughly dried burette with a ground stopcock. .

The corrected solution should be checked again for the content of the substance taken for dissolution. Accurate solutions of hydrochloric acid are also prepared using the ion exchange method, based on an accurately calculated sample of sodium chloride. The sample calculated and weighed on an analytical balance is dissolved in distilled or demineralized water, and the resulting solution is passed through a chromatographic column filled with a cation exchanger in the H-form. The solution flowing from the column will contain an equivalent amount of HCl.

As a rule, accurate (or titrated) solutions should be stored in tightly closed flasks. A calcium chloride tube must be inserted into the stopper of the vessel, filled with soda lime or ascarite in the case of an alkali solution, and with calcium chloride or simply cotton wool in the case of an acid.

To check the normality of acids, calcined sodium carbonate Na2COs is often used. However, it is hygroscopic and therefore does not fully satisfy the requirements of analysts. It is much more convenient to use acidic potassium carbonate KHCO3 for these purposes, dried in a desiccator over CaCl2.

When titrating, it is useful to use a “witness”, for the preparation of which one drop of acid (if an alkali is being titrated) or alkali (if an acid is being titrated) and as many drops of an indicator solution as added to the titrated solution are added to distilled or demineralized water.

The preparation of empirical, according to the substance being determined, and standard solutions of acids is carried out by calculation using the formulas given for these and the cases described above.

Hydrochloric acid is not one of those substances from which it is possible to prepare a solution of exact concentration based on weight. Therefore, an acid solution of approximate concentration is first prepared, and the exact concentration is established by titration with Na 2 CO 3 or Na 2 B 4 O 7.10H 2 O.

1. Preparation of hydrochloric acid solution

According to the formula C(HCl) =

The mass of hydrogen chloride required to prepare 1 liter of acid solution with a molar concentration equivalent to 0.1 mol/l is calculated.

m(HCl) = C(HCl) . Me(HCl).V(solution),

where Me(HCl) = 36.5 g/mol;

m(HCl) = 0.1. 36.5. 1 = 3.65 g.

Since a solution of hydrochloric acid is prepared from concentrated acid, it is necessary to measure its density using a hydrometer and use a reference book to find what percentage the acid of such density corresponds to. For example, density (r) = 1.19 g/ml, w = 37%, then

m(size) = G;

V(solution) = m(solution)/r = 9.85/1.19 = 8 ml.

Thus, to prepare 1 liter of HCl solution, C(HCl) = 0.1 mol/l, measure about 8 ml of hydrochloric acid (r = 1.19 g/ml) using a cylinder (volume 10 - 25 ml) or a graduated test tube ), transfer it to a bottle with distilled water and bring the solution to the mark. The HCl solution prepared in this way has an approximate concentration (» 0.1 mol/l).

2. Preparation of standard sodium carbonate solution

The amount of sodium carbonate required to prepare 100.0 ml of a solution with a molar concentration equivalent to 0.1 mol/l is calculated.

m(Na 2 CO 3) = C e (Na 2 CO 3). Me(Na 2 CO 3).V(solution),

where Me(Na 2 CO 3) = M(Na 2 CO 3)/2 = 106/2 = 53 g/mol;

m(Na 2 CO 3) = 0.1.53.0.1 = 0.53 g.

Preliminarily on technical scales weigh out 0.5–0.6 g of Na 2 CO 3 . Transfer the sample onto a watch glass, previously weighed on an analytical balance, and accurately weigh the glass with the sample. The sample is transferred through a funnel into a 100 ml volumetric flask, and distilled water is added to approximately 2/3 of the volume. The contents of the flask are stirred carefully rotational movements until the sample is completely dissolved, after which the solution is brought to the mark.

3.Standardization of hydrochloric acid solution

To establish the exact concentration of hydrochloric acid, a prepared Na 2 CO 3 solution of exact concentration is used. Due to hydrolysis, an aqueous solution of sodium carbonate has an alkaline reaction:

Na 2 CO 3 + 2H 2 O = 2NaOH + H 2 CO 3 (hydrolysis reaction);

2NaOH + 2HCl = 2NaCl + 2H 2 O;

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Na 2 CO 3 + 2HCl = 2NaCl + H 2 CO 3 (titration reaction).

From the overall equation it is clear that as a result of the reaction, weak energy accumulates in the solution carbonic acid, which determines the pH at the equivalence point:

pH = 1/2 pK 1 (H2CO3) – 1/2 logС (H2CO3) = 1/2 .6.35 – 1/2 log 0.1 = 3.675.

Methyl orange is best for titrations.

The burette is rinsed with the prepared HCl solution and filled almost to the top with a solution of hydrochloric acid. Then, placing a glass under the burette and slightly opening the clamp, fill the lower end of the burette so that there are no air bubbles left in it; the lower meniscus of the HCl solution in the burette should be at zero division. When reading along the burette (and pipette), the eye should be at the level of the meniscus.

Progress of determination. 10.00 ml of the prepared Na 2 CO 3 solution is taken into the titration flask with a pipette, 1-2 drops of methyl orange are added and titrated with HCl solution until the color changes from yellow to orange-pink. The experiment is repeated several times, the results obtained are entered into Table 4, the average volume of hydrochloric acid is found and its molar concentration of equivalent, titer and titer of the substance being determined are calculated.

Instructions

Take a test tube that supposedly contains hydrochloric acid (HCl). Add a little to this container solution silver nitrate (AgNO3). Proceed with caution and avoid contact with skin. Silver nitrate can leave black marks on the skin, which can only be removed after a few days, and salt exposure on the skin acids may cause severe burns.

Watch what happens to the resulting solution. If the color and consistency of the contents of the test tube remain unchanged, this will mean that the substances have not reacted. In this case, it will be possible to conclude with confidence that the substance being tested was not .

If in a test tube appears white precipitate, the consistency of which resembles cottage cheese or curdled milk, this will indicate that the substances have reacted. The visible result of this reaction was the formation of silver chloride (AgCl). It is the presence of this white cheesy sediment that will be direct evidence that initially there was indeed hydrochloric acid in your test tube, and not any other acid.

Pour some of the test liquid into a separate container and drop in a little lapis solution. In this case, a “curdy” white precipitate of insoluble silver chloride will instantly form. That is, there is definitely a chloride ion in the molecule of the substance. But maybe it’s not, after all, but a solution of some kind of chlorine-containing salt? For example, sodium chloride?

Remember another property of acids. Strong acids (and hydrochloric acid, of course, is one of them) can displace weak acids from them. Place a little soda powder - Na2CO3 - in a flask or beaker and slowly add the liquid to be tested. If there is a hissing sound immediately and the powder literally “boils”, there will be no doubt left - it is hydrochloric acid.

Why? Because this reaction is: 2HCl + Na2CO3 = 2NaCl + H2CO3. Carbonic acid is formed, which is so weak that it instantly decomposes into water and carbon dioxide. It was his bubbles that caused this “boiling and hissing.”