| Properties of matter | Oxygen | Acetic acid | Aluminum |
| 1. Physical state under normal conditions | Gas | Liquid | solid |
| 2. Color | No color | No color | Silver white |
| 3. Taste | Tasteless | Sour | Tasteless |
| 4. Smell | Doesn't have | Sharp specific | Doesn't have |
| 5. Solubility in water | Poorly soluble | Soluble | Practically insoluble |
| 6. Thermal conductivity | Low | Small | High |
| 7. Electrical conductivity | Absent | Small | High |
Knowledge of the properties of substances is necessary for their practical use. For example, Figure 6 shows the applications of aluminum due to the properties of this metal.
1. What subjects are considered natural?
2. Give examples of positive human impact on the environment.
3. Give examples of the negative impact of humans on nature.
4. What does chemistry study?
5. From the following list of names, write down bodies and substances separately: snowflake, dew drop, water, piece of ice, granulated sugar, sugar cube, chalk, school chalk. How many bodies and how many substances are named in this list?
6. Compare the properties of substances (that is, establish the common and different between them):
a) carbon dioxide and oxygen;
b) nitrogen and carbon dioxide;
c) sugar and salt;
d) acetic and citric acids.
7. What properties of aluminum underlie its use?
8. Why do they begin to study chemistry later than biology, geography, and physics?
You are starting to get acquainted with a new academic subject - chemistry. What does chemistry study?
As you know from your physics course, many substances are made up of molecules, and molecules are made up of atoms. Atoms are so small that many billions of them can fit on the tip of a needle. However, there are only 114 types of atoms.
Substances such as neon, argon, krypton, and helium are made up of individual isolated atoms. They are also called noble or inert gases because their atoms do not combine with each other and almost do not combine with atoms of other chemical elements. Hydrogen atoms are a completely different matter. They can exist alone (Fig. 4, a), as in the Sun, which more than half consists of individual hydrogen atoms. They can combine into molecules of two atoms (Fig. 4, b), forming molecules of the lightest gas, which, like the chemical element, is called hydrogen. Hydrogen atoms can also combine with atoms of other chemical elements. For example, two hydrogen atoms, combining with one oxygen atom (Fig. 4, c), form molecules of a substance well known to you - water.
Rice. 4.
Forms of existence of the chemical element hydrogen:
a - hydrogen atoms; b - hydrogen molecules; c - hydrogen atoms in a water molecule
Similarly, the concept of “chemical element oxygen” unites isolated oxygen atoms, oxygen - a simple substance whose molecules consist of two oxygen atoms, and oxygen atoms that are part of complex substances. Thus, carbon dioxide molecules contain oxygen and carbon atoms, while sugar molecules contain carbon, hydrogen and oxygen atoms.
Therefore, each chemical element exists in three forms: free atoms, simple substances and complex substances (see Fig. 4).
The concept of “chemical element” is broader, and should not be confused with the concept of “simple substance,” especially if their names are the same. For example, when they say that water contains hydrogen, they mean a chemical element, and when they say that hydrogen is an environmentally friendly type of fuel, they mean a simple substance.
Different substances differ from each other in their properties. So, hydrogen is a gas, very light, colorless, odorless, tasteless, has a density of 0.00009 g/cm 3, boils at a temperature of -253 °C, and melts at a temperature of -259 °C, etc. These properties substances are called physical.
You can describe the physical properties of a substance using the following plan:
- In what state of aggregation (gaseous, liquid, solid) is the substance located under given conditions?
- What color is the substance? Does it have shine?
- Does the substance have an odor?
- What is the hardness of the substance on the relative hardness scale (Mohs scale) (Fig. 5)? (See reference books.)
Rice. 5.
Hardness scale
- Does the substance exhibit plasticity, brittleness, or elasticity?
- Does the substance dissolve in water?
- What is the melting point and boiling point of the substance? (See reference books.)
- What is the density of the substance? (See reference books.)
- Does the substance have thermal and electrical conductivity? (See reference books.)
Laboratory experiment No. 1
Comparison of properties of crystalline solids and solutions
Compare using the one given on p. Plan 10, properties of the samples of substances given to you in cups:
- option 1 - crystalline sugar and table salt;
- option 2 - glucose and citric acid.
Knowing the properties of substances, a person can use them to greater benefit. For example, consider the properties and applications of aluminum (Fig. 6).
Rice. 6.
Application of aluminum:
1 - aircraft manufacturing; 2 - rocket science; 3 - production of power lines; 4 - production of dishes, cutlery and packaging foil
Due to its lightness and strength, aluminum and its alloys are used in aircraft and rocket production; it is not without reason that aluminum is called the “winged metal”.
The lightness and good electrical conductivity of aluminum are used in the manufacture of electrical wires for power lines (power lines).
Thermal conductivity and non-toxicity are important in the manufacture of aluminum cookware.
Non-toxicity and plasticity make it possible to widely use thin sheets of aluminum - foil - as packaging material for chocolate bars, tea, margarine, milk, juices, other products, as well as for medicines placed in contour cells.
The introduction of aluminum alloys in construction increases the durability and reliability of structures.
These examples illustrate that different physical bodies can be made from one substance (aluminium).
Aluminum is capable of burning with a dazzling flame (Fig. 7), so it is used in colorful fireworks and making sparklers (remember N. Nosov’s story “Sparklers”). When burned, aluminum turns into another substance - aluminum oxide.
Rice. 7.
Aluminum combustion is the basis of sparklers and fireworks
Key words and phrases
- Chemistry subject.
- Substances are simple and complex.
- Properties of substances.
- Chemical element and forms of its existence: free atoms, simple substances and complex substances, or compounds.
Work with computer
- Refer to the electronic application. Study the lesson material and complete the assigned tasks.
- Find email addresses on the Internet that can serve as additional sources that reveal the content of keywords and phrases in the paragraph. Offer your help to the teacher in preparing a new lesson - make a report on the key words and phrases of the next paragraph.
Questions and tasks
- Phileo (Greek) means “love”, phobos - “fear”. Give an explanation of the terms “chemophilia” and “chemophobia”, which reflect the sharply opposite attitudes of groups of people towards chemistry. Which one is right? Justify your point of view.
- A mandatory attribute of an infinite number of spy and other detective works is potassium cyanide, more precisely, potassium cyanide, which has the property of paralyzing the nervous system, thereby leading the victim to instant death. Give examples of the properties of other substances that are used in literary works.
- Write down separately the names of substances and the names of bodies from the list given: copper, coin, glass, glass, vase, ceramics, wire, aluminum. Use the hint: for the name of the body - a noun - you can choose a relative adjective formed from the name of the substance, for example: iron and nail - iron nail.
- Write down qualitative adjectives: light, round, long, heavy, hard, odorous, soluble, weighty, concave, soft, liquid, transparent, which can be attributed: a) to substances; b) to bodies; c) both to bodies and substances.
- Compare the concepts of “simple substance” and “complex substance”. Find similarities and differences.
- Determine which of the substances, the molecular models of which are shown in Figure 2, are classified as: a) simple substances; b) to complex substances.
- Which concept is broader - “chemical element” or “simple substance”? Give an evidence-based answer.
- Indicate where oxygen is referred to as a chemical element and where it is referred to as a simple substance:
a) oxygen is slightly soluble in water;
b) water molecules consist of two hydrogen atoms and one oxygen atom;
c) the air contains 21% oxygen (by volume);
d) oxygen is part of carbon dioxide.
- Indicate where hydrogen is referred to as a simple substance and where it is referred to as a chemical element:
a) hydrogen is part of most organic compounds;
b) hydrogen is the lightest gas;
c) balloons are filled with hydrogen;
d) a methane molecule contains four hydrogen atoms.
- Consider the connection between the properties of a substance and its use using the example of: a) glass; b) polyethylene; c) sugar; d) iron.
Getting to know:
Subject: chemistry;
Simple and complex substances;
Properties of substances;
Forms of existence of a chemical element
Chemistry– the science of substances, their properties, transformations of substances and methods of controlling these transformations
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Chemistry subject. Substances.
www.pmedia.ru Lesson motto: “Chemistry stretches its hands wide into human affairs” M.V. Lomonosov
Purpose of the lesson: To introduce: -the subject of chemistry; -simple and complex substances; - properties of substances; -forms of existence of a chemical element.
1. O.S. Gabrielyan. "Chemistry". 8th grade. Textbook. 2. Notebook for work in class and at home. 3. Notebooks for tests and practical work. What is needed for the lesson? Safety precautions!
Natural Sciences 1. What sciences study nature? 2. What biology studies; physics; geography; astronomy; geology? 3. Why did you start studying physics in 7th grade and chemistry in 8th grade?
What does chemistry study? CHEMISTRY STUDIES SUBSTANCES PROPERTIES OF SUBSTANCES TRANSFORMATIONS OF SUBSTANCES “The Father of Chemistry” Robert Boyle (1627 - 1691)
Chemistry is the science of substances, their properties, transformations of substances and methods of controlling these transformations Body Substance Molecules Atoms
Substance is what physical bodies are made of. A chemical element is a certain type of atom. Substances Natural (carbon dioxide) Synthetic (polyethylene) Substances Simple (hydrogen, oxygen) Complex (water, sugar)
Consider models of molecules. What are the similarities and differences between them? Which substance is simple and which is complex? Why? Substances Substance Hydrogen Oxygen Water
Substances that are formed by atoms of one chemical element are called simple
Substances that are formed by atoms of different chemical elements are called complex
Exercise No. 1 Determine which of the proposed substances is simple and which is complex.
What unites these objects?
Substances and bodies
Substances and bodies
Properties of substances are signs by which substances differ from each other or are similar to each other. The subject of chemistry is the study of substances, their transformations, the creation of substances with given properties. Chemistry Application Composition Properties
Exercise No. 2 Indicate where oxygen is spoken of as a chemical element, and where - as a simple substance: A) oxygen is slightly soluble in water; B) water molecules consist of two hydrogen atoms and one oxygen atom; C) the air contains 21% oxygen (by volume); D) oxygen is part of carbon dioxide.
Plan for describing the physical properties of matter 1. In what state of aggregation - gaseous, liquid or solid - is the substance located under given conditions? 2. What color is the substance? Does it have shine? 3. Does the substance have an odor? 4. Does the substance exhibit plasticity, brittleness, or elasticity? 5. Does the substance dissolve in water? 6. What is the melting point and boiling point of the substance? (See reference books.) 7. What is the density of the substance? (See reference books.) 8. Does the substance have thermal and electrical conductivity? (See reference books.)
Exercise No. 3 Describe the physical properties of acetic acid, sugar, salt, copper, aluminum according to the proposed plan. (P.5 (21) textbook)
Chemistry and environmental protection It is necessary to protect and preserve Nature!
Homework Paragraph 1, ex. 1-4 Reports, presentations on the history of the development of chemistry Table Date Achievements of science
Density, heat capacity, properties of oxygen O 2
The table shows the thermophysical properties of oxygen such as density, enthalpy, entropy, specific heat, dynamic viscosity, thermal conductivity. The properties in the table are given for oxygen gas at atmospheric pressure, depending on the temperature in the range from 100 to 1300 K.
Oxygen density is 1.329 kg/m3 at room temperature. When oxygen is heated, its density decreases. The thermal conductivity of oxygen is 0.0258 W/(m deg) at room temperature and increases with increasing temperature of this gas.
Specific heat capacity of oxygen at room temperature is 919 J/(kg deg). The heat capacity of oxygen increases as its temperature increases. Also, when oxygen is heated, the values of its properties such as enthalpy, entropy and viscosity increase.
Note: Be careful! Thermal conductivity in the table is indicated to the power of 10 2. Don't forget to divide by 100.
Thermal conductivity of oxygen in liquid and gaseous states
The table shows the values of the thermal conductivity coefficient of oxygen in liquid and gaseous states at various temperatures and pressures. Thermal conductivity is indicated in the temperature range from 80 to 1400 K and pressure from 1 to 600 atm.
Thermal conductivity values in the table that are above the line refer to liquid oxygen, and those below it refer to gaseous oxygen. According to the table, it can be seen that the thermal conductivity of liquid oxygen is higher than that of gaseous oxygen and increases with increasing pressure.
Dimension W/(m deg).
Thermal conductivity of oxygen at high temperatures
The table shows the values of the thermal conductivity coefficient of oxygen at high temperatures (from 1600 to 6000 K) and pressure from 0.001 to 100 atm.
At temperatures above 1300°C, oxygen begins to dissociate, and at a certain pressure its thermal conductivity reaches maximum values. According to the table, it can be seen that the thermal conductivity of dissociated oxygen at high temperatures can reach values of up to 3.73 W/(m deg).
Note: Be careful! Thermal conductivity in the table is given to the power of 10 3. Don't forget to divide by 1000.
Thermal conductivity of liquid oxygen at the saturation line
The table shows the values of the thermal conductivity coefficient of liquid oxygen at the saturation line. Thermal conductivity is given in the temperature range from 90 to 150 K. It should be noted that the thermal conductivity of liquid oxygen decreases with increasing temperature.
Note: Be careful! Thermal conductivity in the table is given to the power of 10 3. Don't forget to divide by 1000.
Sources:
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2. .
Who knows the formula of water since school days? Of course, that's it. It is likely that from the entire course of chemistry, many who then do not study it in a specialized manner only have the knowledge of what the formula H 2 O means. But now we will try to understand in as much detail and depth as possible what its main properties are and why there is life without it. on planet Earth is impossible.
Water as a substance
The water molecule, as we know, consists of one oxygen atom and two hydrogen atoms. Its formula is written as follows: H 2 O. This substance can have three states: solid - in the form of ice, gaseous - in the form of steam, and liquid - as a substance without color, taste or smell. By the way, this is the only substance on the planet that can exist in all three states simultaneously under natural conditions. For example: at the Earth's poles there is ice, in the oceans there is water, and evaporation under the sun's rays is steam. In this sense, water is anomalous.
Water is also the most abundant substance on our planet. It covers the surface of planet Earth by almost seventy percent - these are oceans, numerous rivers with lakes, and glaciers. Most of the water on the planet is salty. It is unsuitable for drinking and for farming. Fresh water makes up only two and a half percent of the total amount of water on the planet.
Water is a very strong and high-quality solvent. Thanks to this, chemical reactions in water occur at tremendous speed. This same property affects the metabolism in the human body. that the adult human body is seventy percent water. In a child this percentage is even higher. By old age, this figure drops from seventy to sixty percent. By the way, this feature of water clearly demonstrates that it is the basis of human life. The more water in the body, the healthier, more active and younger it is. That’s why scientists and doctors from all countries tirelessly insist that you need to drink a lot. It is water in its pure form, and not substitutes in the form of tea, coffee or other drinks.
Water shapes the climate on the planet, and this is not an exaggeration. Warm ocean currents heat entire continents. This happens due to the fact that water absorbs a lot of solar heat, and then releases it when it begins to cool. This is how it regulates the temperature on the planet. Many scientists say that the Earth would have cooled down and turned into stone long ago if it were not for the presence of so much water on the green planet.
Properties of water
Water has many very interesting properties.
For example, water is the most mobile substance after air. From school courses, many probably remember such a concept as the water cycle in nature. For example: a stream evaporates under the influence of direct sunlight and turns into water vapor. Further, this vapor is transported somewhere by the wind, collects in clouds, or even in and falls in the mountains in the form of snow, hail or rain. Further, the stream runs down from the mountains again, partially evaporating. And so - in a circle - the cycle is repeated millions of times.
Water also has a very high heat capacity. It is because of this that bodies of water, especially the oceans, cool very slowly during the transition from a warm season or time of day to a cold one. Conversely, as the air temperature rises, the water heats up very slowly. Due to this, as mentioned above, water stabilizes the air temperature throughout our planet.
After mercury, water has the highest surface tension. It is impossible not to notice that a drop accidentally spilled on a flat surface sometimes becomes an impressive speck. This shows the viscosity of water. Another property appears when the temperature drops to four degrees. Once the water cools to this point, it becomes lighter. Therefore, ice always floats on the surface of the water and hardens into a crust, covering rivers and lakes. Thanks to this, fish do not freeze out in reservoirs that freeze in winter.
Water as a conductor of electricity
First, you should learn about what electrical conductivity is (including water). Electrical conductivity is the ability of a substance to conduct electric current through itself. Accordingly, the electrical conductivity of water is the ability of water to conduct current. This ability directly depends on the amount of salts and other impurities in the liquid. For example, the electrical conductivity of distilled water is almost minimized due to the fact that such water is purified from various additives that are so necessary for good electrical conductivity. An excellent conductor of current is sea water, where the concentration of salts is very high. Electrical conductivity also depends on the temperature of the water. The higher the temperature, the greater the electrical conductivity of water. This pattern was revealed through multiple experiments of physicists.
Water conductivity measurement
There is such a term - conductometry. This is the name of one of the methods of electrochemical analysis based on the electrical conductivity of solutions. This method is used to determine the concentration of salts or acids in solutions, as well as to control the composition of some industrial solutions. Water has amphoteric properties. That is, depending on the conditions, it is capable of exhibiting both acidic and basic properties - acting as both an acid and a base.
The device used for this analysis has a very similar name - conductivity meter. Using a conductometer, the electrical conductivity of electrolytes in the solution being analyzed is measured. Perhaps it is worth explaining one more term - electrolyte. This is a substance that, when dissolved or melted, breaks down into ions, due to which an electric current is subsequently conducted. An ion is an electrically charged particle. Actually, a conductometer, taking as a basis certain units of electrical conductivity of water, determines its specific electrical conductivity. That is, it determines the electrical conductivity of a specific volume of water taken as an initial unit.
Even before the beginning of the seventies of the last century, the unit of measurement “mo” was used to indicate the conductivity of electricity; it was a derivative of another quantity - Ohm, which is the basic unit of resistance. Electrical conductivity is a quantity inversely proportional to resistance. Now it is measured in Siemens. This quantity got its name in honor of the physicist from Germany - Werner von Siemens.
Siemens
Siemens (can be designated either Cm or S) is the reciprocal of Ohm, which is a unit of measurement of electrical conductivity. One cm is equal to any conductor whose resistance is 1 ohm. Siemens is expressed through the formula:
- 1 cm = 1: Ohm = A: B = kg −1 m −2 s³A², where
A - ampere,
V - volt.
Thermal conductivity of water
Now let's talk about the ability of a substance to transfer thermal energy. The essence of the phenomenon is that the kinetic energy of atoms and molecules, which determine the temperature of a given body or substance, is transferred to another body or substance during their interaction. In other words, thermal conductivity is the heat exchange between bodies, substances, as well as between a body and a substance.
The thermal conductivity of water is also very high. People use this property of water every day without noticing it. For example, pouring cold water into a container and cooling drinks or food in it. Cold water takes heat from the bottle or container, giving away cold in return; a reverse reaction is also possible.
Now the same phenomenon can easily be imagined on a planetary scale. The ocean heats up during the summer, and then, with the onset of cold weather, it slowly cools down and gives off its heat to the air, thereby warming the continents. Having cooled down during the winter, the ocean begins to warm up very slowly compared to the land and gives up its coolness to the continents languishing in the summer sun.
Density of water
It was described above that fish live in a pond in winter due to the fact that the water hardens into a crust over their entire surface. We know that water begins to turn into ice at a temperature of zero degrees. Due to the fact that the density of water is greater than its density, it floats and freezes on the surface.
properties of water
Also, under different conditions, water can be both an oxidizing agent and a reducing agent. That is, water, giving up its electrons, becomes positively charged and oxidizes. Or it acquires electrons and becomes negatively charged, which means it is restored. In the first case, the water oxidizes and is called dead. It has very powerful bactericidal properties, but you don’t need to drink it. In the second case, the water is living. It invigorates, stimulates the body to recover, and brings energy to the cells. The difference between these two properties of water is expressed in the term "oxidation-reduction potential".
What can water react with?
Water is capable of reacting with almost all substances that exist on Earth. The only thing is that for these reactions to occur, you need to provide a suitable temperature and microclimate.
For example, at room temperature, water reacts well with metals such as sodium, potassium, barium - they are called active. With halogens - this is fluorine, chlorine. When heated, water reacts well with iron, magnesium, coal, and methane.
With the help of various catalysts, water reacts with amides and esters of carboxylic acids. A catalyst is a substance that seems to push components towards a mutual reaction, accelerating it.
Is there water anywhere else besides Earth?
So far, no water has been discovered on any planet in the solar system except Earth. Yes, they suggest its presence on the satellites of such giant planets as Jupiter, Saturn, Neptune and Uranus, but so far scientists do not have accurate data. There is another hypothesis, not yet fully verified, about underground water on the planet Mars and on the Earth’s satellite, the Moon. Regarding Mars, a number of theories have been put forward in general that there was once an ocean on this planet, and its possible model was even designed by scientists.
Outside the solar system, there are many large and small planets where, according to scientists, there may be water. But so far there is not the slightest opportunity to be sure of this for sure.
How the thermal and electrical conductivity of water is used for practical purposes
Due to the fact that water has a high heat capacity, it is used in heating mains as a coolant. It ensures heat transfer from producer to consumer. Many nuclear power plants also use water as an excellent coolant.
In medicine, ice is used for cooling, and steam is used for disinfection. Ice is also used in the catering system.
In many nuclear reactors, water is used as a moderator to ensure the successful occurrence of a nuclear chain reaction.
Pressurized water is used to split, break and even cut rocks. This is actively used in the construction of tunnels, underground premises, warehouses, and subways.
Conclusion
It follows from the article that water, in its properties and functions, is the most irreplaceable and amazing substance on Earth. Does the life of a person or any other living creature on Earth depend on water? Absolutely yes. Does this substance contribute to human scientific activity? Yes. Does water have electrical conductivity, thermal conductivity and other useful properties? The answer is also “yes”. Another thing is that there is less and less water on Earth, and especially clean water. And our task is to preserve and protect it (and therefore all of us) from extinction.