1. The source you provided (http://www.dioxin.ru/doc/gn2.1.6.1338-03.htm) is completely unreliable, because This is an invalid version of the document (Resolution No. 114). Current - dated 04/19/2010 N 26. True, the figures for the maximum permissible concentration of naphthalene and in new edition remained the same - 0.003 mg/m3.
2. I cannot trust Onishchenko’s department, because... I have certain reasons for this: Georgian wines, Ukrainian lard and Belarusian milk for some reason very often show maximum permissible concentrations, and ... depending on political situation our power.
3. Document No. 114 itself is quite unscientific and illiterate - no conditions, no exposition, no decoding of abbreviations, etc.
4. Meticulous Americans provide data on the carcinogenicity of naphthalene in experimental animals, and do not indicate a single case of toxic damage in 112,700 workers who were in contact with naphthalene.
5. In graduate school, I spent 3 years modeling toxic hepatitis with carbon tetrachloride. MPC carbon tetrachloride = 0.7 mg/m3. The experiment took place in indoors(vivarium) without any ventilation. And since CCl4 is excreted unchanged by animals, I naturally had to get toxic hepatitis, polyneuritis, and kidney damage. Should... but didn't!
6. I will also share a forty-year observation (!). Department topographic anatomy At the medical institute he constantly works with corpses in formaldehyde. Formalin is a strong neurotoxic poison - MPC is from 0.5 to 0.003 mg/m3 (like Onishchensky naphthalene). The department has a core staff of 4 assistants. For forty years, not one of them was ever sick colds, although they received free milk for being harmful. Everyone has passed the age of 75 and retained their mobility of mind and activity in life! When I used to get sick with a runny nose, I would go to the corpse storage room with the maximum concentration of formaldehyde vapor and breathe through my nose there for 2 minutes (I couldn’t stand it any longer). The runny nose went away in 100% of cases!
7. The American Conference of Governmental Industrial Hygienists gives the level of naphthalene at which a person can live daily without health consequences = 50 mg/m3. Compare with domestic data = 0.003 mg/m3. ???? Those. our naphthalene is super toxic! Three different American departments give the same threshold = 50 mg/m3, and one Onishchenko stands at his own 0.003 mg/m3. I worked with mothballs both as a student and now, I lived with a “mothball” grandmother. If we take Onishchenko’s number as an axiom, then I am already a corpse many times over.
8. The density of naphthalene evaporation is higher than that of air, therefore, even if naphthalene is in your hands, its evaporation goes mainly downward.
9. In your medical practice I have seen about a dozen gasoline poisonings, but not a single naphthalene poisoning. I was present when drivers were poisoned in garages, who sucked gasoline out of gas tanks with their mouths, but grandmothers who sprinkled mothballs on almost everything, did not ventilate the house, and for some reason were not brought to the hospital.
10. I worked as the director of a medical information and analytical center, and what numbers go to Moscow and then end up in the office. I know the documents!
11. As a child, I loved going to my mother’s work. She worked as a head nurse in a hospital. Most of all I loved playing in her office with balls of mercury from thermometers. Sometimes he played for hours, scattered them on the table, the floor, and collected them back into the jar with his hands. My mother only warned me that I shouldn’t put them in my mouth. I didn't take it. My next favorite game was chasing these mercury balls around the box of a broken carbolite tonometer (they were mercury back then). He also loved to steal jars of multivitamins from his mother’s closet; he ate 200 of them a day! After my mother, I went to my father’s work. He is a surgeon who conducted animal experiments in graduate school. What was there: ether, chloroform, nitrous oxide, chloramine, iodine, ammonia. This was real chemical aggression for the body... And nothing! I almost died only once in my life, and that was not from chemicals, but from drinking crayfish with vodka at a wedding - it was a severe allergic reaction! Thanks to the doctors - they pumped me out!
I am not saying that mothballs are not toxic. It is toxic, just like sugar, just like salt, just like arsenic. It all depends on the dose! It was not I who said it, but Paracelsus! I don't spread mothballs all over the garage, but rather store it in a tightly sealed glass jar. When I work with him, I try to stand in the wind.
The main thing in working with any chemical clearly understand what you are dealing with and how to work with it correctly! And I was not only tired of reading political horror stories, but also stopped believing in them.
And my friend became the initiator of a different look at familiar things. I once proved to him, foaming at the mouth, that the dust surrounding us increases the incidence of disease, and that modern technical household innovations (such as television, computers) shorten our lives. He listened to me carefully, accepted all my arguments and facts, and then calmly said: “If this were so, then people would get sick more often in the summer, and not in the fall, when there is less dust, and the life expectancy of the most technically developed country in everyday life, Japan, was would be the lowest, not the longest!”
P. S . In general, I am very pleased with you, as the author of the letter, because you know how to think! Your categorical attitude comes from your youth, but over the course of your life your worldview changes and a message appears to question everything! ;-)
And in your spare time, think about what is more dangerous than a jar of mothballs in the garage or working as a salesman in a department household chemicals(washing powders, solvents, etc.) in a room without ventilation.!? If you have such relatives or friends, share with them your at least theoretical conclusions! ;-)
Naphthalene has an extremely pungent odor, it is obtained from coal tar by distillation, its content in it can vary from 8 to 10%, naphthalene can also be isolated from the products of oil pyrolysis, which is significantly cleaner than coal tar.
Naphthalene was discovered to the world in 1820 by Garden in coal tar. In the same year, studying it physical characteristics took up J. Kidd, who now proposed famous name. In 1826 Faraday established empirical formula substances C5H4, and in 1866 Erlenmeyer proposed a structure of a pair of benzene fused rings.
Application of naphthalene
Since naphthalene is characterized by excellent antiseptic properties, it is used in surgery. It also helps with intestinal diseases, inflammation of the bladder, in the fight against typhoid fever, and has also proven itself as an antipyretic. Today, naphthalene has given way to the most effective insecticides in the fight against moths.
Naphthalene is able to protect against insect bites, including: flies, gadflies, horseflies, etc. It is often used as a preventative when caring for livestock suffering from anthrax.
Chemical and physical properties
According to their own chemical characteristics naphthalene is similar to benzene: it is just as easily sulfonated and nitrated, and also interacts with halogens. What can be distinguished from benzene is that naphthalene is more easily capable of reacting.
Its density is 1.14 g/cm³, the substance begins to melt at 80.26°C, its boiling point is 217.7°C, its solubility in water is 30 mg/l, it spontaneously ignites at 525°C, and its flash point is in the range from 79 to 87°C, and is 128.17052 g/mol.
The effect of naphthalene on human health
Long-term exposure to the substance damages or destroys red blood cells called red blood cells. IARC staff identifies the substance as a possible carcinogen that can lead to cancer diseases in people and animals.
IN human body naphthalene, as a rule, accumulates in adipose tissue, where it is concentrated until it begins to be burned, and the poison begins to penetrate into the blood, which will contribute to poisoning of the body, which can manifest itself in the form of bleeding, the formation of tumors, etc.
Much attention was paid to the mutual transformations of liquids and gases. Now consider the transformation of solids into liquids and liquids into solids.
Melting of crystalline bodies
Melting is the transformation of a substance from a solid to a liquid.
There is a significant difference between the melting of crystalline and amorphous solids. In order for a crystalline body to begin to melt, it must be heated to a temperature that is quite specific for each substance, called the melting point.
For example, at normal atmospheric pressure the melting point of ice is 0 °C, naphthalene - 80 °C, copper - 1083 °C, tungsten - 3380 °C.
For a body to melt, it is not enough to heat it to the melting temperature; it is necessary to continue to supply heat to it, i.e., to increase its internal energy. During melting, the temperature of the crystalline body does not change.
If a body continues to be heated after it has melted, the temperature of its melt will increase. This can be illustrated by a graph of the dependence of body temperature on the time of its heating (Fig. 8.27). Plot AB corresponds to heating solid, horizontal section Sun- melting process and area CD - heating the melt. Curvature and slope of graph sections AB And CD depend on the process conditions (mass of the heated body, heater power, etc.).
Transition crystalline body from a solid to a liquid state occurs abruptly, abruptly - either a liquid or a solid.
Melting of amorphous bodies
This is not how amorphous bodies behave at all. When heated, they gradually soften as the temperature rises and eventually become liquid, remaining homogeneous throughout the entire heating time. There is no specific temperature for the transition from solid to liquid. Figure 8.28 shows a graph of temperature versus time during the transition of an amorphous body from solid to liquid.
Solidification of crystalline and amorphous bodies
Transfer of matter from liquid state into a solid is called solidification or crystallization(for crystalline bodies).
There is also a significant difference between the solidification of crystalline and amorphous bodies. When a molten crystalline body (melt) is cooled, it continues to remain in a liquid state until its temperature drops to a certain value. At this temperature, called the crystallization temperature, the body begins to crystallize. The temperature of the crystalline body does not change during solidification. Numerous observations have shown that Crystalline bodies melt and solidify at the same temperature determined for each substance. With further cooling of the body, when the entire melt has solidified, the body temperature will decrease again. This is illustrated by a graph of the dependence of body temperature on the time of its cooling (Fig. 8.29). Plot A 1 IN 1 corresponds to liquid cooling, horizontal section IN 1 WITH 1 - crystallization process and area C 1 D 1 - cooling of the solid resulting from crystallization.
Substances also transition from liquid to solid during crystallization abruptly without intermediate states.
Hardening of an amorphous body, such as resin, occurs gradually and equally in all its parts; the resin remains homogeneous, i.e. hardening amorphous bodies- this is only a gradual thickening of them. There is no specific curing temperature. Figure 8.30 shows a graph of the temperature of the curing resin versus time.
Thus, amorphous substances do not have a certain temperature, melting and solidification.
Lesson on the topic "Melting and crystallization of bodies."
Goals: formation of the concept of melting and crystallization of bodies, melting and crystallization temperatures; developing the ability to apply acquired knowledge to solving simple problems, developing students’ horizons, nurturing interest in the subject, nurturing a comprehensively developed personality.
Tasks:
Educational - reveal the concepts of melting and solidification; experimentally confirm the obtained theoretical knowledge.
Developmental – create conditions for the development of research and creative skills; communication and collaboration skills.
Educational – contribute to the inculcation of a culture of behavior, create conditions for increasing interest in the material being studied.
Required equipment: interactive whiteboard, projector, monitor.
Explanations: Student responses are in italics in the text.
Lesson plan:
Organizational moment– 2min
Updating knowledge and learning new material - 18 min
Consolidation – 10 min.
Homework– 3min
Lesson summary and grading – 10 min
Reflection – 2 min
PROGRESS OF THE LESSON
1. Organizational moment
– Today in class we will talk about various states substances, we will find out under what conditions a substance can be in one state or another and what needs to be done to transform a substance from one state to another. And so, the topic of today’s lesson is “Melting and crystallization of bodies.” What do you think will be the purpose of our lesson? In the lesson we will learn: Explanation of the processes of melting and solidification of crystalline bodies;
What is the melting and crystallization temperature; What does a graph of melting and solidification of crystalline solids look like?
2. Updating knowledge and learning new material
Teacher: Let's look at the pictures (slide 4). What do you think they have in common?
Students:The pictures show water in three different states: solid, liquid and gas.
Teacher: That's right. Not only water, but also any other substance has three states. What are these states called?
Students:They are called states of aggregation.
A game is played with pictures that depict physical quantities.
While displaying a picture showing λ(specific heat of fusion):
Teacher: what is shown in this picture?
Students:we don't know .
Teacher: today we will get acquainted with a new physical quantity for us called specific heat of fusion. But first, let's think and say, what is melting?
Students:the process of changing a substance from solid to liquid .
Teacher: right!Process The transition of a substance from solid to liquid is called melting.
Teacher: You have 2 glasses on your tables. What do you look at and say?
Students:ice and metal balls .
Teacher: what do you think will happen to these substances by the end of the lesson?
Students:the ice will melt .
Teacher: Well done. Let's consider the melting process using a fragment. Your job is to notice whether the temperature changes during this process.
Students:The temperature does not change during the melting process .(slide 5)
Teacher: What is the melting point, let’s find it in the textbooks on page 146?
Students:The temperature at which a substance melts is called the melting point.
Teacher: That's right. Do you think it is possible for a substance to undergo a reverse transition from a liquid to a solid state?
Students:Yes .
Teacher:The transition of a substance from a liquid to a solid state is called solidification, or crystallization (slide 6)
Teacher: Let's look at this process with the help of video. Did the temperature change throughout the curing process?
Students:The temperature did not change during the hardening process.
Teacher: Let's rememberthat during the process of melting and solidification the temperature of the substance does not change . This means that the melting point is the temperature above which a substance cannot exist in a solid state. Look at the temperature table that is on your tables and answer me the questions:
1)Which of the substances indicated in the table has the most high temperature melting? (Tungsten)
2) What is the melting point of aluminum? (660)
3)What is the melting point of copper? (1083)
4) Is it possible to melt copper in an aluminum vessel? (No)
5) What metals can be melted in a copper vessel? (iron, platinum, cast iron)
6) In what state (solid or liquid) are silver and tungsten at a temperature of 1000°C? (silver is liquid, tungsten is solid).
Teacher: Using the graph (slide 7), we will consider the process of transition of ice from a solid to a liquid state.
Observation of the process began from the moment when the ice temperature was -20 OC. With further heating, the temperature of the ice increased until it reached 0 OC. At this moment, the ice began to melt, and its temperature stopped rising. During the entire melting time, the temperature of the ice did not change, although energy continued to be supplied to it.
Upon reaching 20 OThey stopped imparting energy to the substance: the water began to cool, and at 0 OThe process of water crystallization began. During the entire curing time, the temperature of the substance did not change again. It is also clear from the graph thatthat the melting temperature is equal to the crystallization temperature.
Guys, there is such a legend:
A young businessman bought a container of mercury thermometers at a low price in Africa and decided to make big money by selling these thermometers in Norilsk, where, as he heard, there is a great need in winter for thermometers to determine the outside air temperature every day. Arriving in Norilsk, he received a container and decided to sell all the mercury thermometers to organizations within a week.
Do you think he received the money?
Students:say their options .
Teacher: When he printed out the contents of the container, he found that he was almost broke. The temperature in Norilsk on this winter day was minus 45 degrees.
He discovered that the mercury thermometers of the entire container had burst.
Why do you think?
Students: (if students find it difficult to answer a question, the teacher gives a hint using a table)Mercury froze at minus 39 degrees and glass tubes containing frozen mercury burst.
Teacher: Studying melting various substances of the same mass, you can see that to turn them into liquid it takes different quantities warmth. For example, in order to melt 1 kg of ice taken at a temperature of 0 degrees, you need to expend 333 kJ of energy. And in order to melt a lead block weighing 1 kg, how much energy do you need to spend? Let's look at the table.
Students: 25 kJ.
Teacher: (Slide 9)A physical quantity showing how much heat is needed to transform 1 kg crystalline substance taken at the melting point into a liquid of the same temperature is called specific heat of fusion .
The specific heat of fusion is measured in and denoted by the Greek letter λ (lambda).
To find the amount of heat required to melt a crystalline body of arbitrary mass, the specific heat of fusion of this body must be multiplied by its mass:
Q = λ · m .
The amount of heat released by the body is considered negative. Therefore, when calculating the amount of heat released during the crystallization of a substance with a massm , you should use the same formula, but with a minus sign:Q = –λ · m .
3. Consolidation
1. Teacher: Let's look at the leaves that are on your tables.
The figure shows a graph of changes in the temperature of naphthalene.
a) What state of naphthalene corresponds to the segment of the BC graph? (heating)
b) How long did the heating of liquid naphthalene last? (4 minutes)
c) To what temperature was naphthalene heated? (110 degrees)
2. Let's look at the second picture. It shows a graph of the temperature of tin.
a) How does the temperature of tin change in sections AB, BC and CD? (increased, did not change, increased)
b) What state of tin corresponds to the segment of the BC graph? (melting of tin)
3 . You have the conditions of the problem written on your sheets, let’s solve it.
What amount of heat is required to melt 0.8 kg of aluminum taken at its melting point?
Given: aluminumm – weight = 0.8 kg
λ – specific heat
melting aluminum =
= 391 kJ/kg = 391,000 J/kg.
Solution:
From the table, which shows the melting points of different substances, we see that the melting point of aluminum is 660 °C. This means that aluminum is taken at the melting point, so the problem is solved in one step:
Q = λ · m = 391 J/kg 0.8 kg =
312,800 J.
Answer:Q = 135,000 J of heat.
4. Divide into two teams and whichever team solves the problem faster wins. Conditions of the problems on the sheet.
4. Homework
Problem: What amount of heat is required to melt 7 kg of copper taken at the melting point? Draw a graph of copper temperature versus time.
*Additional task : Using the knowledge gained in class, create a crossword puzzle.
5. Lesson summary
– What did you study in class today?
Which new one? physical quantity have you studied?
What are the units for measuring the specific heat of fusion of a substance?
Which new formula did you study it today?
Let's look into our cups. What has changed there since the beginning of the lesson?
What is called melting?
What is the melting temperature of ice?
What is the melting point of paraffin? (paraffin demonstration)
– Giving grades for work in class.
– Well done! The lesson is over! (slide 11)
6. Reflection (slide 10):
" Smile"
Students are offered pictures depicting: imbued with a sad, melancholy mood; the other - joyful, cheerful. Students choose the picture that matches their mood.
Is everything clear from the lesson or do you still have questions?
List of resources used:
Peryshkin A.V. Physics. 8th grade :textbook for general education institutions. – M.: Bustard, 2008.
Kirik L.A. Physics – 8. Multi-level independent and tests. – M.: “Ilexa”, 2010.
