Dilution and mixing of sulfuric acid. Calculations for diluting and concentrating solutions How to properly dilute sulfuric acid with water

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 the 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 a warm room. When the oleum melts and turns into an oily liquid, it must be taken out into the air and there poured into a smaller container, using the method of squeezing with air (dry) or an 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.

Solid organic acids are used in laboratory practice. 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.

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 to wear protective equipment for your body and face, as concentrated acids cause severe chemical burns. To calculate the required amount of 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 running water for 15-20 minutes. Don't start work 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 with a 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.

1. Are the following statements true about the rules of safe work in the school laboratory?

And -we always have to re-zi-new gloves.

B. Experiments with le-tu-chi-mi, poisonous substances are carried out only under traction.

1) only A is true

2) only B is true

3) both statements are true

2. Which of the gases that are present in the at-mo-sphere in the re-zul-ta-te de-i-tel-no-sti of a person is the most more tok-si-chen?

1) CO2 2) NO23) CH4 4) H2

3. What mixture can be filtered?

1) sa-ha-ra and water

2) sand and water

3) water and gasoline

4) sand and sa-ha-ra

4. Are the assumptions about safe handling of chemical substances correct?

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

5. Are the following statements true about the rules of work in the school lab?

A. On any container in which substances are stored, there should be these boxes with names or shapes -la-mi substances.

B. Experiments with hot-ryu-chi-mi and edible substances are not-about-ho-di-mo carried out in glasses - your own or la-bo -ra-tor-nykh.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

6. Are the following conclusions about the rules of safe work in the hi-mi-che-la-bo-ra-to-ria correct?

B. Sulfuric acid should be dissolved in hot water.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

7. Are the following conclusions about pure substances and mixtures and ways of dividing them correct?

A. Pure substances have a constant composition.

B. A mixture of boiled salt and river sand can be diluted by adding water and then fil-tro-va-niya and you-pa-ri-va-niya.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

8. Are the following statements about car exhaust gases true?

A. The most harmful component of exhaust gases is CO2, since it is a vapor gas.

B. Nitrogen oxides are formed through the interaction of a car with nitrogen air -Ha.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

9. Are the following conclusions about the rules of safe work in the hi-mi-che-la-bo-ra-to-ria and with pre-pa-ra-ta-mi would-how chemistry?

A. In la-bo-ra-to-rii, the sourness in the solution is determined by the taste.

B. When working with pre-pa-ra-ta-mi of chemistry, containing alkali, not-about-ho-di-mo is-used -re-new gloves.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

10. Are the assumptions about the ability to create mixtures correct?

A. A mixture of ethanol and water can be diluted using a funnel.

B. The effect of a mag-ni-tom on a mixture of iron and alu-mi-ni-e opi-locks is in a physical way -de-le-tion of substances.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

11. Are the following conclusions about the interaction with gases in the process of laboratory experiments correct?

A. Before you set fire to the water, you shouldn’t check it for cleanliness.

B. Chlorine, which is obtained from salt, cannot be determined by its smell.

1) Only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

12. Are the following conclusions about the rules of safe work in La-bo-ra-to-ria correct?

A. When heating the sample with a solution of boiled salt, do not use protective glasses.

B. When transferring the liquid into the sample, you can close the hole of the sample with your hand.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

13. Are the following conclusions about the process of filtration and the use of chemical re-acs correct? -tsiy hu-lo-ve-kom?

A. To speed up the filtering process, the beveled end of the funnel should be pressed against the wall. -th hundred-ka-na.

B. At the core of the melting of iron and steel there are oxidation reactions.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

14. Sodium chloride can be isolated from its aqueous solution using

1) filtering

2) you-pa-ri-va-niya

3) magician

4) from-sta-i-va-niya

15. Are the assumptions about the ability to create mixtures correct?

A. Sea water can be purified from salts dissolved in it with the help of filtering.

B. Per-re-gon-ka is revealed in a hi-mi-che-like way of dividing mixtures.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

16. Are the judgments about the rules of using and storing pre-pa-ra-tov household chemicals correct?

A. Aero-zo-li, is-used as a means to fight against those who are on us, safe for children and animals.

B. Products and detergents should be stored in places accessible to children.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

17. Are the judgments about safe handling of chemical substances correct?

A. The broken mercury thermometer and the mercury that leaked from it should be thrown into the trash bin.

B. Paint, containing lead ions, should not be used to cover children's toys and su-doo.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

18. Are the following conclusions about the rules of safe work in the hi-mi-che-la-bo-ra-to-ria correct?

A. Methane forms explosive mixtures with air.

B. Dissolve sulfuric acid by adding water to it.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

19. Are the following statements about pure substances and mixtures true?

A. Natural gas is a pure substance.

B. Diamond is a mixture of substances.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

20. Are the following statements about water true?

A. Sea water has a greater density than river water, since it contains a significantly larger amount of water. content of dissolved salts.

B. Water is filled with memory, so water can be used for recording information.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

21. Are the following conclusions about the rules of storing and receiving vitamins correct?

A. Vi-ta-min C can be consumed in an unlimited quantity.

B. It is possible to store and receive vi-ta-mi-nas in a non-limited period of time.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

22. Are the following statements about carbon dioxide gas true?

A. The amount of carbon gas in the at-mo-sphere is growing bla-go-da-rya-tel-no- sti che-lo-ve-ka.

B. Carbon dioxide is the most harmful component of exhaust gases.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

23. What elements in drinking water are most toxic for humans?

1) sodium and calcium chlorides

2) sulfate calcium and magnesium

3) salts of lead and mercury

4) created-my car-bo-na-you

24. Are the following statements true about the rules of work in the school lab?

A. Substances found in la-bo-ra-to-ria are prohibited from tasting, even if they in everyday life they are consumed in food (for example, sodium chloride).

B. When acid appears on the skin, the affected area should be washed with a large amount of alkali solution.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

25. Are the following statements true about the rules of safe work in the school lab?

A. To extinguish the flame of alcohol, it should be blown out.

B. When heating the sample with the solution, it should be kept strictly vertical.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

26. Are the following statements true about the rules of work in the school lab?

A. All experiments carried out in la-bo-ra-to-ria must be recorded in the la-bo-ra-tor journal.

B. When heating liquid and solid substances in test tubes and flasks, you cannot direct them towards yourself and others .

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

27. Are the following conclusions about the rules of storing vi-ta-mins and pre-knowing my means correct? ?

A. Storing vi-ta-mi-novs does not require strict adherence to the rules specified in the instructions.

B. To remove grease stains from the surface of the surface, use my products properties that have an alkaline environment.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

28. Are the judgments about safe handling of chemical substances correct?

A. The broken mercury thermometer and the mercury that leaked from it should be thrown into the trash bin.

B. Kras-ka-mi, with-k-hold-mi-containing lead, do not re-co-men-du-s-cover children's games- Rush-ki and po-su-doo.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

29. Are the following conclusions about the rules of safe work in the hi-mi-che-la-bo-ra-to-ria correct?

A. In la-bo-ra-to-ria you can’t be familiar with the smell of substances.

B. Water can be boiled in any glass sous-de.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

30. Are the assumptions about safe handling of chemical substances correct?

A. The broken mercury thermometer and the mercury that leaked from it should be thrown into the trash bin.

B. Kras-ka-mi, with-k-hold-mi-containing lead, do not re-co-men-du-s-cover children's games- Rush-ki and po-su-doo.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

31. Are the following statements about ozone true?

A. Ozone in the stra-t-sphere absorbs part of the ul-tra-fi-o-le-to-of-radiation, protecting from it from -lu-che-nii living or-ga-niz-we.

B. Ozone is a completely harmless gas, which is why it is preferred to use it instead of chlorine for water purification.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

32. Are the judgments about environmental safety true?

A. It is not recommended to eat fruits and vegetables grown from iron ore. roads and highways.

B. Vegetable plants grown with the use of everyday mineral amenities are not - pose a danger to the or-ga-niz-ma of a person.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

33. Are the assumptions about the ability to create mixtures correct?

A. You-pa-ri-va-nie from-to-fi-zi-che-skim sp-so-bam di-de-le-niya mixtures.

B. Dividing the mixture of water and eta may be possible through filtering.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

34. Are the following conclusions about the rules of safe work in the hi-mi-che-la-bo-ra-to-ria and storing substances in everyday life?

A. When the solution dissolves sour on the skin, it should be washed with water and dis-solved with the solution. howl of soda.

B. An easy-to-re-flame liquid, for example ace-tone, can only be stored ko in ho-lo-dil-ni-ke.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

35. Are the following conclusions about the ways of dividing mixtures correct?

A. To separate a mixture of river sand and iron filings, you can use magnet.

B. To remove sediment from the solution, you can use filter paper.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

36. Are the following statements about water true?

A. Water-based water contains a mixture of soluble salts - sulphate and hydro-car-bo-na-tov.

B. Water has a memory, which is why it has mechanical influences, for example, sound sounds. ba-nia, its properties change.

1) only A is true

2) only B is true

3) both statements are true

4) both statements are incorrect

37. Are the following conclusions about the rules of safe work in the hi-mi-che-la-bo-ra-to-ria correct?

A. You can heat water in a men-zur-ka.

B. Burning sodium can be extinguished with water.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

38. Are the following conclusions about the ways of co-breathing gases in la-bo-ra-to-ria correct?

A. Carbon-acidic gas can be collected in a vessel by removing the air.

B. Acid can be collected in a vessel both by removing air and by removing water.

1) Only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

39. Are the following conclusions about the ways of obtaining coal-le-acid gas in La-bo-ra-to-ria correct?

A. Coal-le-acidic gas in la-bo-ra-to-rii is dissolved in car-bo-na-that calcium when heated -va-nii.

B. For laboratory experiments, carbon-acidic gas is obtained by heating car-bo-na-ta am-mo-niya .

1) Only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

40. Are the judgments about the environmental safety of chemical production correct?

A. You throw away sulfuric gas, which is formed in the process of obtaining sulfuric acid , have a positive influence on the health of man, the plant and animal world.

B. The processing of lead ores does not pose a threat to the environment and human health. lo-ve-ka.

1) only A is true

2) only B is true

3) both judgments are true

4) both judgments are incorrect

When concentrated sulfuric acid and water are mixed, a lot of heat is generated. For a chemist, this fact is very important, since both in the laboratory and in industry it is often necessary to prepare dilute solutions of sulfuric acid. To do this, you need to mix concentrated sulfuric acid with water - not always, but often.

How to mix concentrated sulfuric acid and water?

All textbooks and workshops strongly recommend pour sulfuric acid into water (in a thin stream and with good mixing) - and not vice versa: Do not pour water into concentrated sulfuric acid!

Why? Sulfuric acid is heavier than water.

If you pour acid into water in a thin stream, the acid will sink to the bottom. The heat that is released during mixing will dissipate - it will go to heating the entire mass of the solution, since a large amount of water is located above the layer of acid that has sank to the bottom of the vessel.

The heat will dissipate, the solution will heat up - and nothing bad will happen, especially if the liquid is mixed well while adding acid to water.

What will happen if you do wrong , - add water to concentrated sulfuric acid? When the first portions of water enter the sulfuric acid, they will remain on the surface (since water is lighter than concentrated sulfuric acid). Will stand out many heat that will be used to heat small quantity water.

The water will suddenly boil, resulting in splashes of sulfuric acid and the formation of a caustic aerosol. The effect can be similar to adding water to a hot frying pan with oil. Sulfuric acid splashes can get into your eyes, skin and clothing. Sulfuric acid aerosol is not only very unpleasant to inhale, but also dangerous to the lungs.

If the glass is not heat-resistant, the vessel may crack.

To make this rule easier to remember, they come up with special rhymes like:

“First water, and then acid - otherwise big trouble will happen!”

They also use special phrases for memorization - “memes”, for example:

"Tea with lemon."

Books are good, but I decided to film what the result of incorrectly mixing concentrated sulfuric acid and water looks like in practice.

Of course, with all precautions: from safety glasses to the use of small quantities of substances.

I conducted several experiments - I tried mixing sulfuric acid with water (both correctly and incorrectly). In both cases, only strong heating was observed. But boiling, splashing, and the like did not happen.

As an example, I will describe one of the experiments conducted in a test tube. I took 20 ml of concentrated sulfuric acid and 5 ml of water. Both liquids are at room temperature.

I started adding water to the sulfuric acid. The water boiled only at the moment when the first portions of water were added to the acid. New portions of water extinguished the boil. The caustic aerosol flew (I was not prepared for this, I had to move away for a few seconds). I tried to mix it with an aluminum wire (what I had on hand). Zero effect. I measured the temperature with a thermometer. It turned out to be 80 degrees Celsius. The experiment was hardly a success.

The new experiment was carried out in a flask: so that the contact surface of the two liquids was maximum (this would ensure a sharper release of heat), and the thickness of the water layer above the sulfuric acid was minimal. I did not add water all at once, but in small portions (so that the heat would be used to boil the water, and not to heat the entire mass of water).

So, about 10-15 ml of concentrated sulfuric acid was poured into a conical flask. I used about 10 ml of water.

While I was preparing for the experiment, the acid, under the scorching sun, warmed up to 36-37 degrees (which is 20 degrees higher than the initial temperature of the acid in the previous experiment). The water in the test tube also warmed up slightly, but not so much. I think this played a big role in the success of the experience.

When the main portion of water was added to the sulfuric acid, splashes and a caustic aerosol were noticeably flying. Fortunately, they were carried away by the wind, which was blowing from my side, so I didn’t even feel anything.

As a result, the temperature in the test tube rose above 100 degrees!

What conclusions can be drawn? If you break the rule that Do not add water to concentrated sulfuric acid , splashing does not always occur, but it is possible - especially when the water and acid are warm. Especially if you add water slowly, in small portions and in a wide container.

When working with larger quantities of water and acid, the likelihood of sudden heating and splashing increases (reminder: we only took a few milliliters).

Experience that demonstrates that Do not add water to concentrated sulfuric acid , described in the workshop of the authors Ripan and Ceteanu.

Let me quote:

If water is poured into concentrated sulfuric acid, the first drops of water that fall into it instantly turn into steam and splashes of liquid fly out of the vessel. This happens because water, having a small specific gravity, is not immersed in the acid, and the acid, due to its low heat capacity, does not absorb the released heat. When hot water is poured in, a stronger splash of sulfuric acid is observed.

Experience.Mixing water with concentrated H 2 SO 4. A glass of concentrated sulfuric acid is placed at the bottom of a large glass covered with a funnel. Warm water is poured in using a pipette (Fig. 161). When hot water is poured in, the inner walls of a large glass and funnel are instantly covered with splashes of liquid.

Rice. 161

In the absence of a glass funnel, you can use a cardboard one, into which a pipette with water is inserted.

If concentrated sulfuric acid is poured dropwise or in a thin stream into a glass of water, you will notice how the heavier sulfuric acid sinks to the bottom of the glass.

When concentrated H 2 SO 4 is mixed with ice, two phenomena can be simultaneously observed: hydration of the acid, accompanied by the release of heat, and melting of ice, accompanied by the absorption of heat. Therefore, as a result of mixing, either an increase or decrease in temperature can be observed. Thus, when mixing 1 kg of ice with 4 kg of acid, the temperature rises to almost 100°, and when mixing 4 kg of ice with 1 kg of acid, the temperature drops to almost -20°.

How to mix two liquid substances? For example, some acid and water? It would seem that this problem is from the series “twice two is four.” What could be simpler: drain the two liquids together in some suitable container, and that’s it! Or pour one liquid into a container that already contains another. Alas, this is the same simplicity that, according to an apt popular expression, is worse than theft. Because things can end extremely sadly!

Instructions

There are two containers, one of them contains concentrated sulfuric acid, the other contains water. How to mix them correctly? Should we pour acid into water or, conversely, water into acid? The price of a wrong decision in theory can be a low score, but in practice - at best, a severe burn.

Why? But because concentrated sulfuric acid, firstly, is much denser than water, and secondly, it is extremely hygroscopic. In other words, it actively absorbs water. Thirdly, this absorption is accompanied by the release of a large amount of heat.

If water is poured into a container with concentrated sulfuric acid, the first portions of water will “spread” over the surface of the acid (since water is much less dense), and the acid will begin to greedily absorb it, releasing heat. And there will be so much heat that the water will literally “boil” and splashes will fly in all directions. Naturally, without avoiding the hapless experimenter. Getting burned with “clean” boiling water is not very pleasant, but considering that the water spray will probably still contain acid. The prospect is becoming completely gloomy!

That is why many generations of chemistry teachers forced their students to literally memorize the rule: “First water, then acid! Otherwise, big trouble will happen!” Concentrated sulfuric acid should be added to water in small portions with stirring. Then the unpleasant situation described above will not happen.

A reasonable question: it’s clear with sulfuric acid, but what about other acids? How to properly mix them with water? In what order? It is necessary to know the density of the acid. If it is denser than water, for example, concentrated nitrogen, it should be added to water, just like sulfur, observing the above conditions (little by little, with stirring). Well, if the density of the acid differs very slightly from the density of water, as is the case with acetic acid, it makes no difference.

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