Candle. Burning candle

1) Light one ordinary cylindrical candle, which we use for household needs. Observe the process of burning the candle. What does a burning candle give us?

2) Create conditions so that the candle flame is calm. Look carefully at the steady candle flame and describe your observations. Mirror the shape of the candle at the wick.

3) Create a small breeze in one direction (blow softly), describe your observations. What changes have occurred with the candles?

4) Repeat steps 2 and 3 of your experiment using a candle that does not have the shape of a regular cylinder or is covered with grooves, or a shaped candle, as well as a scented candle of an ordinary cylindrical shape.

5) Describe your observations and draw conclusions.

Conclusions.

1) The air above the candle flame heats up, expands and becomes less dense and lighter than the cold air surrounding it. Warm air rises and cold air takes its place. There is a constant flow of air, the stream of which cools the substance from which the candle is made from all sides; its outer layer is much cooler than the middle. The middle melts from the flame, which reaches the wick to the point below which it goes out. The outer part of the candle does not melt.

2) A cup of regular shape is formed due to a uniform upward air flow acting on the entire outer surface of the candle and preventing it from heating up.

3) When burning a candle that does not have the correct shape and is covered with grooves, a cup with smooth edges cannot be obtained, due to the unevenness of the air flow and the poor shape of the cup that is formed, so paraffin flows down the candle and drips form.

4) When an aromatic candle burns, the smell of citrus fruit spreads throughout the room due to a very interesting and important physical phenomenon - diffusion (the mutual penetration of molecules of one substance between the molecules of another substance).

5) Fuel enters the flame due to a phenomenon called wetting (the attraction of molecules to each other in a solid and liquid). A wick impregnated with wax or paraffin is made from cotton threads that have capillaries with a diameter smaller than a hair. Through these capillaries, the liquid rises due to the additional pressure that arises. The fuel is transferred to the place where combustion occurs, and not just somehow, but ideally to the center of the flame.

(All conclusions summarizing student responses on the slides)

Experience No. 2. « Study of the structure of flame"

Work order(TB instruction)

1) Let’s light the candle again and consider what structure the flame has. Select three zones: the bottom of the flame, the middle part and the outer part of the flame. Try to notice that each zone is a different color from each other. Describe the flame color of each zone, fill out table 1.

2) Observe the difference in temperature of each zone. To do this, place matches in different zones of the flame and pay attention to the rate of ignition of the match head. Record the ignition time using a stopwatch, fill in the columns in Table 1.

Table 1

Student response: Flame structure? The flame has a somewhat elongated appearance, at the top it is brighter than at the bottom near the wick.

Flame color?

Ignition time? (fill out the table on the board).

Teacher: (Summarizing student responses on slides). When a match is placed in the lower zone of the flame, ignition occurs in 1.04 seconds; when a match is placed in the middle zone of the flame, ignition occurs in 0.9 seconds; When a match is inserted into the outer part of the flame, ignition occurs in 0.1 seconds. Therefore, the lower zone has a lower temperature, while the middle and outer zones have higher temperatures. Using reference literature, we note: the lower zone has a temperature of 7000 C, the middle zone has 11,000 C, the outer zone has 14,000 C. We can conclude for ourselves that To quickly heat something, you need to use the top of the flame and not just candles.

(output on slides)

To make sure that different zones of the flame have different temperatures, another experiment can be carried out. Place a splinter (or cleaned match) into the flame so that it crosses all three zones. We will see that the splinter is more charred where it hits the middle and upper zones. This means the flame is hotter there. (together with the teacher)

Experiment No. 3 “Detection of combustion products in a flame” (together with the teacher) (TB instruction)

Work order

Let us determine the composition of each zone of the candle flame.

Teacher: During the first two experiments, you observed the combustion process and noted for yourself that in the lower zone of the candle flame there is gaseous paraffin. Write this down in your table and move on to experiment #3.

(output on slides)

1) Place a tin plate fixed in a holder into the middle zone of the candle flame and hold it for 5-7 seconds. Let's quickly pick up the record. The bottom plane of the plate is smoked.

Conclusion: The lower plane of the tin plate is smoked because the paraffin does not burn completely, resulting in the formation of soot - this is pure carbon. (output on slides)

2) Fix a dry, cooled, but not fogged test tube in a holder, turn it upside down and hold it over the flame until it fogs up.

Small droplets of water appear on the walls of the test tube. Then, quickly pour lime water into the same test tube.

Conclusion: Water condenses in a test tube. After we pour lime water into the test tube, we notice that the lime water becomes cloudy. Consequently, the combustion products of candle paraffin are carbon dioxide and water. Let's compose paraffin candle burning diagram:

Paraffin + oxygen = water + carbon dioxide. (on slide)

Based on the results of the experiment, we will draw up a table . (work at the board)

table 2

Teacher: Let's determine once again what supports the process of burning a candle. To do this, let’s perform the following experiment No. 4.

Experience No. 4 "The influence of air on the combustion of a candle"

Equipment: candle, glass, glass jar with a capacity of 0.5 liters, glass jar with a capacity of 3 liters.

The order of work.

1. Light a candle and cover it with a glass, measure its burning time.

2. Light the candle and cover it with a 0.5 liter glass jar and measure the burning time.

3. Light the candle and cover it with a 3-liter glass jar and measure the burning time.

4. Present the data in table form and draw a conclusion.

Table 3

Conclusion. The combustion of a candle depends on the oxygen contained in the air and the greater the volume of air, the longer the candle burns. (output on slides)

ILiterature review

1. The history of the creation of a candle……………………………………………………………………………………………………………2

   Types of candles……………………………………………………………………………………………………………………………………...3

   Soap making……………………………………………………………………………………………………………….…..4

IIexperimental part

2.1 Physical analysis of candles………………………………………………………………………………………………………….………..5

2.2 Where is the hottest part of the candle?………………………………………………………………………………….…….6

2.3 What burns in a candle? ……………………………………………………………………………………………………………..6

2.4 Chemical analysis of candle combustion products………………………………………………………….…….6

IIIMaking and practical use of candles

3.1 Making candles…………………………………………………………………………………………………………..7

3.1.1 Wax candle

3.1.2 Paraffin candle

3.1.3 Stearic suppository

3.2 Obtaining soap from stearin…………………………………………………………………………………………8

Conclusions………………………………………………………………………………………………………………………………… …..8

Conclusion

Bibliography

Applications

Introduction

Although candles have long been replaced by electric lamps, they are still in use and create a festive mood for the New Year, and sometimes help out during an unexpected power outage. Nowadays, candles can be found in a variety of colors and shapes. They are used for decorative purposes, for scenting rooms, and for measuring time. Candles have also found their use in religion. Church candles and candles in Buddhism have a thin, elongated shape and are made of wax. Many famous artists used the theme of candles, the play of light and shadow in their work. Boris Pasternak wrote the famous poem “Winter Night”, written in 1946, the main character of which is a candle. So magical and attractive, known to man since ancient times, they have becomethe topic of my project.

The relevance of research: Candles originated in ancient times, but even now they are still popular: they create a festive mood for the New Year and save us during an unexpected power outage. Despite the fact that a candle is the most common item for us, we know little about it.

Research objectives:

Analyze scientific literature on this topic

Compare the physical properties of candles made from different materials

Find out where the hottest part of the flame is and what exactly is burning in the candle.

Conduct a chemical analysis of combustion products of candles made from various materials

Make candles of various materials with your own hands

Make soap

I Literature review

1.1 History of the creation of the candle.

Candles were invented by man a long time ago, but for a long time they were used only in the homes of rich people and were expensive. The combustible material for a candle can be: lard, stearin, wax, paraffin, spermaceti or another substance with suitable properties (fusibility, flammability, solid). The prototype of a candle is a bowl filled with oil or fat, with a sliver of wood as a wick (later, fiber or fabric wicks were used). Such lamps gave off an unpleasant odor and produced a lot of smoke. The first candles of modern design appeared in the Middle Ages and were made from tallow (most often) or wax. Wax candles have long been very expensive. To illuminate a large room, hundreds of candles were required; they smoked, blackening the ceilings and walls. In the 15th century, beeswax slowly began to increase in popularity as a combustible material for candles. In the 16th-17th centuries, American colonists invented the production of wax from some local plants, and candles produced in this way temporarily gained great popularity - they did not smoke, did not melt as much as tallow ones, but their production was labor-intensive, and popularity soon faded to No. The development of the whaling industry in the late 18th century brought the first major changes to the candle-making process because spermaceti (a waxy oil obtained from the top of the sperm whale's head) became readily available. Spermaceti burned better than fat and did not smoke, and in general was closer to beeswax in properties and advantages. Most of the inventions that influenced the candle making industry date back to the 19th century. In 1820, the French chemist Michel Chevrolet discovered the possibility of isolating a mixture of fatty acids from animal fats - the so-called. stearin Stearin, otherwise sometimes called stearic wax due to wax-like properties, turned out to be hard, tough and burned without soot and almost odorless, and the technology for its production was not expensive. And as a result, soon stearin candles almost completely replaced all other types of candles, and mass production was established. Around the same time, the technology of impregnating candle wicks with boric acid was mastered, which eliminated the need to frequently remove wick residues (if not removed, they could extinguish the candle). Closer to the beginning of the 20th century, chemists were able to isolate petroleum wax - paraffin. Paraffin burned cleanly and evenly, giving off virtually no odor (the only strong smell was the smoke produced when extinguishing the candle, but this smell was not very unpleasant), and it was cheaper to produce than any other combustible substance for candles known at that time. Its only drawback was its low melting point (compared to stearin), due to which the candles tended to float before they burned, but this problem was solved after they began to add harder and more refractory stearin to the paraffin. Even with the introduction of electric lighting for quite a long time at the beginning of the 20th century, paraffin candles were only gaining popularity, this was facilitated by the rapid development of the oil industry at that time. Over time, their importance in lighting changed to decorative and aesthetic.

Today, paraffin candles are almost the only type among candles. Candles are made from a mixture of highly purified (snow-white or slightly transparent) paraffin with a small amount of stearin, or from low-purified (yellow) paraffin, both with and without the addition of stearin. The former are more aesthetically pleasing and less odorous, the latter do not float so much. Occasionally, candles are made from unrefined paraffin (red-yellow) without additives, which float very much and are therefore not in demand.

1.2 Types of candles

When making candles the following are used:

Paraffin - waxy mixture of saturated hydrocarbons (mineral wax) with composition from C 18 N 38 to C 35 N 72 . It has low chemical activity and is poorly soluble in water. The product of petroleum distillation is the most popular material for candles, and in one form or another is included in most candles. In the 19th century, stearin significantly replaced it as a candle material.

Beeswax - a natural product produced by bees. Simple lipids (esters of higher fatty acids and higher high molecular weight alcohols). Beeswax consists mainly of the ester of palmitic acid and myricyl alcohol. The wax is very stable, insoluble in water, but soluble in gasoline, chloroform, and ether. Beeswax candles burn longer and brighter than paraffin candles and are preferred by connoisseurs because they are natural. Due to the higher cost of wax candles, candles are often not made entirely from beeswax, but rather it is added to other materials to extend the burning time of the candle and imitate the natural aroma. The wax used for candles comes in different types.

Stearin - stearic acid with an admixture of palmitic, oleic and other saturated and unsaturated fatty acids. It is added to paraffin so that it shrinks more and when it cools, candles cast from it are easier to remove from the mold. Stearine also prevents candles from melting. For some time, stearin was the main material for making candles until they learned to extract paraffin from crude oil.

Glycerol - used in a mixture with gelatin and tannin. Glycerin candles are completely transparent; they can be given any color using different dyes. Inside a glycerin candle you can place various compositions of colored paraffin, which gives the candle extraordinary decorative properties.

Fat , for example beef. In some countries, due to the fight against obesity, they are trying to find other uses for this fat other than food. Sodium nitrate (up to 5%) and potassium alum (up to 5% by weight) are usually added to fat suppositories. Candles burn cleanly, without smoke or soot.

1.3 Soap making

Soap was invented much earlier than gunpowder and paper, no one knows when and no one knows by whom. It happened for the first time when melted fat, dripping from roasting meat, fell onto wood ash. The fat was immediately partially hydrolyzed, forming fatty acids that combined with sodium and potassium salts in the ash. These compounds were actually soap. This is the first surfactant. Soap production was put on a scientific basis at the beginningXIXcentury. This was facilitated by numerous studies of the French chemist M. Chevral in the field of fat chemistry. Chevreul established that the basis of any soap is fats, chemical compounds of glycerol with higher fatty acids. In the middleXIXcenturies, chemists could accurately name the composition of all soaps obtained and used. Since then, soap production has not undergone fundamental changes. The cleansing effect of soap is a complex process. The molecule of the salt of a higher carboxylic acid has a polar ionic part (-COONa) and a nonpolar hydrocarbon radical. The polar part of the molecule is soluble in water (hydrophilic), and the non-polar part is soluble in fats and other low-polar substances (hydrophobic). Under normal conditions, particles of fat or oil stick together, forming a separate phase in an aqueous environment. In the presence of soap, the picture changes dramatically. The non-polar ends of the soap molecule dissolve in the oil droplets, while the polar carboxylate anions remain in the aqueous solution. As a result of the repulsion of like charges on the surface of the oil, it is broken into tiny particles, each of which has an ionic shell of COO anions - . The presence of this shell prevents the particles from coalescing, resulting in the formation of a stable oil-in-water emulsion. Emulsification of fat and grease containing dirt is responsible for the cleansing effect of soap.

II experimental part

2.1 Physical analysis of candles

For physical analysis, we took candles from various materials and compared their properties.

Observations

Wax candle

Paraffin candle

Stearic suppository

Appearance of the candle

Yellow-brown solid

Off-white solid

White solid

Candle burning time

Burns longer

Burns less

Burns longer

Presence of odor when burning

Gives off a faint honey smell

No

No

Soot formation during combustion

Smokes less

Smokes more

Smokes less

Flame brightness

Almost the same

Candle melting when burning

Floats less

Floats more

Floats less

2.2 Where is the hottest spot of the flame?

At first glance it seems to be in the very center. We checked this by holding a sheet of paper over the middle of the candle flame, across it. There should be no drafts in the room so that the flame is even and does not fluctuate.

Research results

A charred, ring-shaped area appeared on the paper. It was narrower the higher the paper was held, and it turned into a solid spot at the level of the upper third of the flame - this is where its hottest place is located. This seemingly strange result turns out to be quite obvious if we remember that oxygen is necessary for combustion. It enters the flame only from the periphery, and only there does the combustion reaction occur. Therefore, the temperature of the flame in its different parts is different.

2.3 What burns in a candle

Probably the material from which it is made (paraffin, stearin or wax). But if we turn a burning candle over, the material will flow along the wick and, instead of flaring up, extinguish it. So what burns in a candle? We carefully blew out the candle, breathing lightly on it. A thin stream of bluish smoke trailed from the wick. They brought a match to her.

Research results

The flame along this stream from a distance of 1-2 centimeters jumped to the wick and the candle lit up again. What we mistook for smoke was paraffin vapor (stearin or wax) - it is they that burn in the candle. The molten paraffin material (stearin or wax) rises through the wick, like water through a thin capillary. The flame of a match evaporates it and ignites the vapor. The wick serves only as a “pipeline” supplying fuel to the “firebox” - the tongue of the flame.

2.4 Chemical analysis of candle combustion products

Soot detection: We fixed the glass slide in the holder, brought it into the area of ​​the dark cone of a burning candle and held it for 3 seconds. They quickly raised the glass and examined the lower plane. A dark spot will indicate the presence of soot.

Water detection: The dry test tube was secured in a holder, turned upside down and held over a flame until it fogged up. A fogged wall of the test tube will indicate the formation of water.

Carbon dioxide detection: 2 ml of lime water was added to the same test tube. The formation of carbon dioxide was determined by the cloudiness of the lime water.

Research results

Combustion products

Wax

Paraffin

Stearic

Soot

+

+

+

Water

+

+

+

Carbon dioxide

+

+

+

Combustion reaction equations

Wax candle 2 C 15 H 31 COOC 31 H 63 + 139 O 2 =94 CO 2 + 94 H 2 O

Paraffin candle 2C 16 H 34 +49 O 2 =32 CO 2 + 34 H 2 OC 17 H 36 + 26 O 2 =17 CO 2 + 18 H 2 O

Stearic suppository C 17 H 35 COOH+ 26O 2 =18O 2 + 18H 2 O

III Production and practical use of various types of candles.

3.1 Making candles with your own hands

3.1.1 Wax candle

A wax candle was made from beeswax. Beeswax can be purchased from honey sellers. For production, we chose the “twisting” method: the wick is pulled horizontally and evenly covered with wax, softened in warm water. When the workpiece reaches the required thickness, they begin to roll it on a smooth board with a flat board to give the future candle a cylindrical shape. Then the candle is cut from the bottom and its top is pulled out.

3.1.2 Paraffin candle

Since it is not possible to obtain paraffin on our own, to make a paraffin candle of the required size, we took a ready-made paraffin candle and made a new one from it using the casting method. To do this, we made a mold and secured the wick in it. The mold can be made from any material that can withstand heating up to 50 degrees. The walls of the mold were smeared with dishwashing liquid and allowed to dry. The paraffin, heated in a water bath to a liquid state, was carefully poured into the mold and allowed to cool. The slower a paraffin candle cools, the less likely it is to crack. After cooling completely, carefully remove the candle from the mold.

3.1.3 Stearic suppository

First, we obtained a concentrated soap solution. To do this, the soap was ground on a grater. Soap shavings were placed in a container, water was added and heated, stirring with a wooden stick, until completely dissolved. After this, while still heating and stirring the solution, vinegar was poured in. After adding the acid, a white mass immediately floated to the surface. This is stearic acid. The reaction mixture must be acidic, otherwise not all soap will react with the acid. Therefore, acid must be taken in excess. The reaction of the medium was easily checked using litmus paper. After the mixture cooled, the stearin was collected on the surface. The resulting liquid under the stearin is a solution of sodium sulfate or sodium acetate. The stearin was scooped out with a spoon and washed with water to remove excess acid. We dried the mass and wrapped it in a cloth. Stearin is ready! A stearin candle can be made in a mold by securing a wick in it in advance and pouring melted stearin into the mold. You can also prepare a candle by dipping, then you don’t need a mold. A wick is dipped into the melted stearin (you can take a thread from a wick for kerosene gas or a kerosene stove). I take out the wick, and when the stearin hardens on it, I put it back into the solution. This operation is repeated several times until the candle of the required thickness grows on the wick. Reaction equation for producing stearin from soap:C 17 H 35 COONa+ CH 3 COOH= C 17 H 35 COOH+ CH 3 COONa

3.2 Making soap from a candle

We took several pieces of stearin candle. Melt the stearin in a water bath and add a saturated soda solution. A solid white mass immediately formed. This is sodium stearate, that is, soap itself. The mixture was heated for several minutes to allow the reaction to take place as completely as possible. Then we placed a mold (matchbox) and poured the resulting mass. After the soap has cooled, remove it from the mold. Reaction equation for producing soap from stearin: 2C 17 H 35 COOH+ Na 2 CO 3 =2 C 17 H 35 COONa+ H 2 O+ CO 2 .

Conclusions:

Analyzed and studied scientific literature on this topic

I compared the physical properties of candles made from different materials: wax and stearin candles have the best physical properties.

The hottest part is found at the top third of the candle flame. The reason a candle burns is not the combustion of the material, but the formation of vapors during combustion.

Based on the chemical analysis of combustion products, I found out that they all form soot, water and carbon dioxide, i.e. they are organic substances.

I made candles from various materials with my own hands.

I made soap from a stearin candle.

Conclusion

Wax and stearin candles have the best physical properties: they not only smoke and float less, but also burn longer. Paraffin candles have a cost advantage (they are slightly cheaper than wax and stearin candles), which is why they are the most common in our country. The most burning part is at the level of the upper third of the flame, and what burns in a candle is not the material from which it is made, but the vapors formed during combustion. When burned, all candles produce soot, water and carbon dioxide, i.e. they are organic substances.

Bibliography

Michael Faraday "The Story of a Candle" 1982

Gabrielyan O.G. "Chemistry. 8th grade" Moscow 2002

Gabriel O.G. "Chemistry. 10th grade" Moscow 2014

Magazine “Science and Life”, article “The candle was burning on the table” No. 6, 2014

Magazine "Young Chemist Club", article "Soap from a candle and a candle from soap"

Magazine "Chemistry and Life", article "While the candles are burning"

• 1. Smoking will occur when there is insufficient oxygen content in the combustion atmosphere. I don’t know how to do it, maybe. add water vapor.
  2. In a large jar, the oxygen was not completely burned out, but some percentage of it remained, so the left candle burned longer than ideal.
• Michael,
  1. An exact solution is needed for the first question. The general direction of thought is correct - combustion with a lack of oxygen, but it didn’t work out that way for me. I tried just covering the jar with a lid, the flame just gradually went out, and that was it. There is no smoking.
  2. I don’t think there will be any oxygen left in the big jar. The flame causes strong mixing throughout the entire volume. Hot carbon dioxide rises up - cools down from the can - falls down. Plus, its density is 1.5 times greater than that of air, so it will also sink down.
• Apparently some of the carbon dioxide has gone down from the 3 liter bottle. Most likely, the experiment will be successful if you seal the jar with a piece of plastic lid and turn it over before closing it with cardboard.
  P.S.
  CO2 = 46
  Air = 29
  Total difference is 1.5 times
  You can light a candle, for example, by a chemical reaction of potassium permanganate with sulfuric acid
  KMnO4 + H2SO4 (conc.)
  the resulting oxide, when interacting with paraffin, will ignite it
• As for the procedure: I think the answers should have been hidden so that the “second” ones would not see the answers of the “first”, so that there would be no disputes - it’s a competition, after all

  Essentially: there’s nothing else in my head, there’s no way to surf the Internet right now...

• Mikhail, openness of comments is normal. The first correct answer still counts.
  There is no need to scour the Internet, there is more logic and basic knowledge of physics and chemistry. And, of course, imagine all the nuances of the experiment in your head.
• On the second question: – “Why does the left candle burn for so long?” for some reason there is still no comment about the intensity of combustion, if you look at the video it is noticeable that when burning with a large amount of carbon dioxide
  gas flame is smaller.
  Regarding the first question, there is an assumption that perhaps the candle will smoke when the wick is long, i.e. the wick burns and burns oxygen around it.
• Sergey, I agree. It is very difficult to make a quantitative assessment here. Who said that the flame of both candles burns equally intensely? By eye, they seem to be the same, but maybe one consumes more oxygen than the other. And secondly, the flame attenuation processes themselves. As a result, it turns out that we can only give a qualitative assessment (“yes, the left candle burns less”), but not a quantitative assessment.

• Andrey

  4 August 2010, 06:01

  Regarding the combustion. The candle “eats” not all the oxygen, but very little. I had a need to organize an oxygen-free atmosphere, and I was just thinking of making it a candle, but I read on the cave-dwelling forums that if a candle goes out in a closed cave, it means there is only a couple of percent less oxygen. Well, there’s only two or three percent carbon dioxide there, or what? I do not remember.
  Well, besides, there is such a thing as convection. Carbon dioxide is heavier than air and collects from below, while the air above is thus somewhat richer in oxygen. This is what allowed the candle to burn longer
  I can’t tell you how to make it smoke, offhand, you have to play around with it.
• Andrey, I didn’t understand how the idea about convection and the fact that “Carbon dioxide is heavier than air and collects from below, while the air above is thus somewhat richer in oxygen.”. If there is strong convection from the flame, as I wrote above, then everything inside the jar is quickly mixed, and it doesn’t matter where everything is collected.

  Anatoly, you can also bring any object into the middle zone of the flame, where incomplete combustion occurs. Then the soot is deposited on the object. This is how glass is smoked. You can also see this here:

  Here you can clearly see how the rod and the plastic bag are smoked.

  I’m still waiting for the last correct answer, where the excess oxygen could have come from in the closing jar. Hint: think in terms of thermal expansion of gases.

• (got it because the pressure in the bank began to drop)
• Regarding the first question, I think there is already an answer. It is necessary to do some kind of manipulation so that incomplete oxidation occurs: it could be, for example, an object brought up—the vapors of burning paraffin will cool sharply, without having time to burn completely (this is still a cold object). If I'm not mistaken, it seems like it could work with the addition of some chemicals to the candle wick.
  Regarding the second point:
  In general, the combustion of a candle in this case can be considered as an inertial link of the nth order. In the simplest case, if the rate of oxygen combustion is directly proportional (although it can be proportional to the square, cube... concentration). In this case, the less oxygen in the can, the slower it burns. In general, VCO2(t)=K1*e^(–k2/t). This non-linear equation for carbon dioxide explains why, with 0.5 liters of “clean” air, a candle will burn twice as long as with 2.5 liters - it’s just that the combustion will be very intense at first and almost 2 liters of air are used in the first 10 seconds and as in the second case, only 0.5 liters will remain, which will burn out for another 30 seconds.

• esfir

  January 2, 2014, 06:37

  Quote: “Wax candles must have a loosely woven wick from thick fibers; for all other candles, the wicks are made from tightly woven threads. This is due to the viscosity of the candle mass in the molten state: viscous wax requires wide capillaries, and easily moving paraffin, stearin and fats require thinner capillaries, otherwise due to excess combustible material the candle will begin to smoke heavily."
  Option: place a piece of loose rope into the paraffin melted near the wick.
• I noticed that it starts to smoke when the wick is slightly moistened, i.e. The heating temperature of the wick itself is below average when burning dry wicks. The flame itself, naturally, has a normal temperature, because oxygen burns, and the wick only supports the combustion. You have to spit on your finger, run it along the wick and set it on fire - it will smoke
• All this is very interesting. But, "great minds", can you answer another question? While the candle is burning, it has no smell. And this is normal, because pure water and carbon dioxide have no odor. But! Once you extinguish the candle, you will get a strong unpleasant smell! Incomplete combustion produces the same water, pure carbon C and CO instead of CO2, but C and CO are also odorless. Then why does it stink so much when we put out a candle?

• January 5, 2017, 06:15

  Pavel, as I understand it, it smells like the products of incomplete combustion of paraffin. That is, at the moment the candle is extinguished, there should be a fairly large range of all sorts of molecular compounds.

Lesson format: research with elements of interdisciplinary integration.

You cannot change someone by passing on ready-made experience.
You can only create an atmosphere conducive to human development.
K. Rogers

The purpose of the lesson: look at the candle flame and at the candle itself through the eyes of a researcher.

Lesson objectives:

Begin the formation of the most important method of understanding chemical phenomena - observation and the ability to describe it;

Show during practical work the significant differences between physical and chemical reactions;

Update basic knowledge about the combustion process, taking into account the material learned in the lessons of other academic disciplines;

Illustrate the dependence of the candle combustion reaction on the reaction conditions;

Begin developing the simplest methods for conducting high-quality reactions to detect candle combustion products;

Develop cognitive activity, observation, broaden horizons in the field of natural science and artistic and aesthetic knowledge of reality.

Lesson steps:

I Organizational moment. Teacher's opening speech.

Candle? - a traditional device for lighting, which is most often a cylinder of solid combustible material (wax, stearin, paraffin) serving as a kind of reservoir of solid fuel, supplied in molten form to the flame with a wick. The ancestors of candles are lamps; bowls filled with vegetable oil or fusible fat, with a wick or just a sliver for lifting fuel into the combustion zone. Some peoples used wicks inserted into raw fat (even the carcass) of animals, birds or fish as primitive lamps. The first wax candles appeared in the Middle Ages. Candles have been very expensive for a long time. To illuminate a large room, hundreds of candles were required; they smoked, blackening the ceilings and walls. Candles have come a long way since their creation. People have changed their purpose and today people have other light sources in their homes. But, nevertheless, today candles symbolize a holiday, help create a romantic atmosphere in the house, calm a person, and are an integral part of the decor of our homes, bringing comfort and coziness into the house. A candle can be made from pork or beef fat, oils, beeswax, whale oil, and paraffin, which is obtained from oil. Today it is easiest to find candles made from paraffin. We will conduct experiments with them today.

II Updating students' knowledge.

Briefing. Safety regulations

Conversation:

Light a candle. You will see how the paraffin begins to melt near the wick, forming a round puddle. What process is taking place here? What happens when a candle burns? After all, paraffin simply melts. But where does the heat and light come from then?

What happens when a light bulb comes on?

Students' answers.

Teacher:

When paraffin simply melts, there is no heat or light. Most of the paraffin burns, turning into carbon dioxide and water vapor. Because of this, warmth and light appear. And the heat melts part of the paraffin, because it is afraid of hot things. When the candle burns out, there will be less paraffin left than there was at first. But when an electric light bulb burns, heat and light are also released, but the light bulb does not get smaller? The burning of a light bulb is not a chemical, but a physical phenomenon. It does not burn on its own, but converts electricity into light and heat. As soon as you turn off the electricity, the light goes out. All you have to do is light the candle, and then it burns itself.

And now our task is to look at the candle flame and at the candle itself through the eyes of a researcher.

III Studying new material.

Experiment “Structure of a candle”

Experience “Study of the physical and chemical processes that occur when a candle burns”

Experiment “Study of the structure of a candle flame. Detection of combustion products in a flame. Observation of flame heterogeneity”

Experiment “Studying the dependence of the height of a candle flame on the length of the wick”

Experiment “Proof of candle burning in air oxygen”

Experiment “The influence of air on the combustion of a candle. Watching the flame of a burning candle"

Experiment “Study of the smoke of an extinguished candle”

Experiment “Qualitative reaction for detecting candle combustion products”

IV Consolidation of the studied material.

Frontal survey:

List the sequence of processes in which a candle burns.

What phase transformations are observed when a candle burns?

What is the combustible material of a candle?

What is a cotton wick used for?

What phenomenon allows liquid paraffin to rise to a certain height?

Where is the hottest part of the flame?

Why does the candle length decrease?

Why does the candle flame not go out, although during combustion substances are formed that do not support combustion?

Why does a candle go out when we blow on it?

What conditions are necessary for a longer and better burning candle?

How can you put out a candle? What properties are these methods based on?

What is the qualitative reaction to carbon dioxide?

Teacher:

Consideration of the structure and combustion of a candle convincingly illustrates the complexity of the most trivial everyday objects around us, testifies to how inseparable sciences such as chemistry and physics are. A candle is such an interesting object of study that it is impossible to consider the topic exhausted.

At the end of our lesson, I would like to wish you that, like a candle, you radiate light and warmth for those around you, and that you are beautiful, bright, and necessary, like the candle flame that we talked about today.

V Homework.

1. Assignment for those wishing to carry out research work at home:

Take for experience any thing that has a zipper. Open and close the zipper several times. Remember your observations. Rub a paraffin candle onto a zipper, for example, on a sports jacket. (Don't forget to ask your mom for permission when you take the jacket for the experiment). Has the movement of the zipper changed?

Answer the question: “Why do they sometimes rub zippers with a candle?”

(The substances from which the candle column is made (stearin, paraffin) are a good lubricant that reduces friction between the fastener links.)

2. Assignment for those wishing to carry out research work at home.

Take 3 candles of different composition, made of paraffin, wax, stearin. You can buy candles in the store, or you can make them yourself. (Ask Mom or Dad to watch the experience with you.) Wait until dusk, place the candles close to each other and light them. Fill in the table as you observe the burning candles.

References.

1. Faraday M.., History of a candle, M., Nauka, 1980.

Small pieces of a crystalline substance were placed in the device shown in the figure. X white and poured liquid Y. After opening the tap, the liquid Y fell from the funnel into the lower part of the device and came into contact with the substance X, a reaction began, accompanied by the release of a colorless gas Z. Gas Z it flowed through a gas outlet tube into a glass, at the bottom of which lighted candles of various heights were installed (see Fig. 1.1).

As the glass fills with gas Z the candles went out.

1. What gas was obtained in the device shown in the figure? What is the name of this device?
2. What substances may be X And Y? Write an equation for the possible reaction between X And Y with education Z.
3. Why did the candles start to go out? In what order did they go out? Why? Is this property of gas Z any application?
4. If gas Z passed into lime water, turbidity is first observed due to the formation of a white precipitate. However, further transmission Z leads to complete dissolution of the initially deposited precipitate. Explain this phenomenon, illustrate your answer with the corresponding reaction equations.
5. If in a vessel filled with gas Z, add burning magnesium, the metal will continue to burn. What substances are formed? Write an equation for this reaction.
6. Substances known to react with gas Z, and oxygen is released. Give two examples of such substances and the corresponding reaction equations.

Answer:

1. We received carbon dioxide (gas Z) in the Kipp apparatus.

2 points

1. Substance X– insoluble carbonate, for example calcium carbonate; pieces of marble are often used in laboratory practice. Y– an acid that forms soluble calcium salts, such as hydrochloric acid. Possible interaction option:

CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2

1 point

1. The candles go out because carbon dioxide does not support combustion ( 0.5 points). Carbon dioxide is heavier than air, so the smallest candle will go out first, followed by gradually taller candles as the glass fills with CO 2 . ( 1 point) This property of carbon dioxide is used in the operation of carbon dioxide fire extinguishers. ( 0.5 points)

2 points

1. When carbon dioxide is passed into lime water, a calcium carbonate precipitate is observed:

Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O

With an excess of CO 2, the precipitate dissolves, because a soluble acid salt is formed:

CaCO 3 + CO 2 + H 2 O = Ca(HCO 3) 2

2 points

1. When magnesium burns in carbon dioxide, magnesium oxide and soot are formed:

2Mg + CO 2 = 2MgO + C

1 point

1. Carbon dioxide reacts with peroxides and superoxides:

• 2Na 2 O 2 + 2CO 2 = 2Na 2 CO 3 + O 2
• 4KO 2 + 2CO 2 = 2K 2 CO 3 + 3O 2

2 points

Total 10 points.

Task 2 “Composition of Glauber’s salt”

A 28.6 g sample of partially weathered Glauber's salt (sodium sulfate crystalline hydrate) was dissolved in water and an excess of barium chloride solution was added. 23.3 g of precipitate formed. Determine the formula of the original salt.

Answer:

Task 3 “Analysis of inheritance”

The young chemist Vasya decided to investigate a certain alloy that he inherited from his grandmother. To begin with, Vasya tried to dissolve the alloy in hydrochloric acid, but discovered that no dissolution occurred. Then he tried to dissolve it in hot concentrated nitric acid. In this case, the alloy collapsed, the solution turned blue, but a colored sediment remained at the bottom, which did not dissolve even after prolonged heating in nitric acid. Vasya filtered the precipitate and dried it. Having placed the powder in a crucible and heated it until it melted, and then cooled it, Vasya immediately realized what substance was the insoluble precipitate.

1. What two metals does the alloy that Vasya studied consist of?
2. How to dissolve the precipitate formed when an alloy is heated in nitric acid? Give the reaction equation.
3. How to isolate the second component of the alloy from the blue solution obtained after reaction with nitric acid? Give the necessary reaction equations.

Answer:

1. Copper (by the color of the solution) and gold (insolubility in nitric acid and the characteristic appearance of a compact metal) by 2 points
2. Dissolution in aqua regia 1 point

Reaction equation:

Au + HNO 3 (conc.) + 4HCl (conc.) = H + NO + 2H 2 O 4 points

(Options with hydrochloric acid and chlorine, selenic acid, a mixture of nitric and hydrofluoric acids, etc. are also suitable - give full marks.)

1. Any reasonable method, for example:

Fe + Cu(NO 3) 2 = Cu + Fe(NO 3) 2 1 point

Total 10 points.

Task 4 “Isomeric reagents and products”

Two isomeric hydrocarbons A And IN contain 90.57% carbon (by weight).

During oxidation with a hot acidified solution of potassium permanganate A And B oxidize into substances C And D, which are also isomers, and the substance WITH actively used in the production of polymers. Substance WITH is quite stable when heated, and heating a substance D leads to the formation of a substance E, which can also be obtained by hydrocarbon oxidation F(mass fraction of carbon 93.75%) with oxygen on vanadium(V) oxide.

1. Set the formulas of substances A–F and write the equations for all the reactions mentioned.
2. What polymer is obtained from substance C? Where is it used?

Answer:

From the mass fraction of carbon we find the gross formula A And IN:

ν(C) : ν(H) = (90.57/12) : (9.43/1) = 4: 5,

C4H5. There is no odd number of hydrogen atoms in hydrocarbons, so the molecular formula is A And IN– C 8 H 10. These can be ethylbenzene or dimethylbenzenes (xylenes). Isomeric oxidation products can only form from xylenes.

Substance C– oxidation product A– used in the production of polymers, most likely it is terephthalic acid, then A– 1,4-dimethylbenzene (para-xylene).

Substance D– oxidation product B– when heated, it splits off water, most likely it is phthalic acid, which when heated turns into cyclic anhydride, then B– 1,2-dimethylbenzene (ortho-xylene).

Gross formula of hydrocarbon F:

ν(C) : ν(H) = (93.75/12) : (6.25/1) = 5: 4,

C 5 H 4 , however, in oxidation reactions there is no increase in the number of carbon atoms, therefore, F contains at least 8 carbon atoms.

Doubling the indices we get that F– C 10 H 8, naphthalene.

Reaction equations:

Polymer– polyethylene terephthalate (PET) – used, for example, for the production of plastic bottles.

Grading system:

Problem 5 “Isomeric reagents, but different products”

Two isomeric hydrocarbons A And B upon addition of bromine, they form 1,2,3,4 – tetrabromobutane and 1,1,2,2 – tetrabromobutane, respectively. Hydrocarbon A during severe oxidation, it destructs to carbon dioxide. Hydrocarbon B under the same conditions it gives propanoic acid and carbon dioxide.

1. Determine the structure of isomers A And B.
2. Give equations for the reactions of bromination of isomers A And B.
3. Give equations for the reactions of hard oxidation of isomers A And B. Explain why, under conditions of severe oxidation, the isomer A destructurizes to carbon dioxide.
4. Suggest qualitative reactions that can be used to distinguish isomers A And B.

Answer:

1. Isomer A: H 2 C = CH – CH = CH 2 butadiene–1,3

Isomer B: HC ≡ C – CH 2 – CH 3 butine-1

2. Bromination of isomers A And B

A: H 2 C = CH – CH = CH 2 + 2Br 2 → CH 2 Br – CHBr – CHBr – CH 2 Br

1,2,3,4 – tetrabromobutane

B: HC ≡ C – CH2 – CH 3 + 2Br 2 → CHBr 2 – CBr 2 – CH 2 – CH 3

1,1,2,2 – tetrabromobutane

3. Severe oxidation of isomers A And B can be done using an acidified solution of potassium permanganate or a chromium mixture (K 2 Cr 2 O 7 ∙H 2 SO 4) as an oxidizing agent.

A: 5H 2 C = CH – CH = CH 2 + 22KMnO 4 + 33H 2 SO 4 → 20CO 2 + 11K 2 SO 4 + 22MnSO 4 + 48H 2 O

During vigorous oxidation, carbon dioxide and oxalic acid are formed at the intermediate stage of the oxidation reaction of 1,3-butadiene. This dicarboxylic acid exhibits reducing properties and is oxidized to carbon monoxide IV. (This reaction is used in analytical chemistry to determine the exact concentration of potassium permanganate.)

H 2 C = CH – CH = CH 2 HOOC – COOH HCOOH CO 2 + H 2 O

B: 5HC ≡ C – CH 2 – CH 3 + 8KMnO 4 + 12H 2 SO 4 → 5CO 2 + 5CH 3 – CH 2 –COOH + 4K 2 SO 4 + 8MnSO 4 + 12H 2 O

4. Reactions to identify isomers A And B. When terminal alkynes react with an ammonia solution of silver oxide or chloride

copper(I), silver or copper acetylenides are easily formed, which precipitate from solution.

HC ≡ C – CH 2 – CH 3 + OH → AgС ≡ С – CH2 – CH 3 ↓ + 2NH 3 + H 2 O

HC ≡ C – CH 2 – CH 3 + Cl → CuС ≡ С – CH 2 – CH 3 ↓ + NH 4 Cl + NH 3

Isomer A does not give such reactions.

Grading system:

Task 6 “Qualitative analysis”

Four numbered test tubes contain solutions of phenol, sodium acetate, glucose and acetamide (acetic acid amide). Determine the contents of each test tube by selecting the appropriate reagents for analysis.

To solve the problem, make a table of the results of a thought experiment, which will indicate visual signs of the reactions occurring.

Table schema:

Give the reaction equations used to identify the organic compounds indicated in the problem.

Answer:

It is possible to use other reagents.

To form phenols, you can use a reaction with bromine water or a solution of iron(III) chloride.

C 6 H 5 OH + 3Br 2 (aq. solution) → C 6 H 2 Br 3 OH ↓ white precipitate + 3HBr

Phenol solution + FeCl 3 solution → violet color of the solution.

Acetamide can be determined by the release of ammonia when a sample of the substance is heated with an alkali solution.

CH 3 CONH 2 + KOH → CH 3 COOK + NH 3

Glucose is easily detected by the appearance of a bright blue color when interacting with an alkaline solution of copper(II) hydroxide without heating.

In this case, glucose exhibits the properties of a polyhydric alcohol. The color of the solution is due to the formation of a copper complex compound. When the blue solution is heated, a red precipitate of copper(I) oxide is formed.

HOCH 2 (CHOH) 4 CHO + 2Cu(OH) 2 HOCH 2 (CHOH) 4 COOH + Cu 2 O + 2H 2 O

Glucose (as a reducing carbohydrate) can also be detected using the “silver mirror” reaction.

HOCH 2 (CHOH) 4 – COH + 2OH → HOCH 2 (CHOH) 4 – CONH 4 + 2Ag + 3NH 3 + H 2 O

Sodium acetate can be identified by elimination because it does not react with any of the listed reagents. However, we can prove that we are dealing with a salt of a carboxylic acid using a test for the formation of esters: a small amount of alcohol (for example, ethanol) and a few drops of concentrated sulfuric acid are added to the salt solution and heated slightly. If the mixture is poured into water, drops of an ester with a characteristic odor will appear on the surface.

CH 3 COONa + C 2 H 5 OH + H 2 SO 4 → CH 3 COOC 2 H 5 ethyl acetate + NaHSO 4 + H 2 O

Grading system:

Out of 6 problems, 5 solutions for which the participant
scored the highest points, that is one of the problems with the lowest score is not
taken into account.