Lesson objectives:
- Experimentally prove and formulate the law of conservation of mass of substances.
- Give the concept of a chemical equation as a conditional recording of a chemical reaction using chemical formulas.
Lesson type: combined
Equipment: scales, beakers, mortar and pestle, porcelain cup, alcohol lamp, matches, magnet.
Reagents: paraffin, CuSO solutions 4 , NaOH, HCl, phenolphthalein, iron and sulfur powders.
Progress of the lesson.
I. Organizational stage.
II. Setting a goal.State the topic and purpose of the lesson.
III. Checking homework.
Review questions:
1. How do physical phenomena differ from chemical ones?
2. What are the areas of application? physical phenomena You know?
3. What signs can be used to judge what has happened? chemical reaction?
4. What are exo- and endothermic reactions? What conditions are necessary for their occurrence?
5. Students report the results of a home experiment (No. 1,2 after §26)
Exercise. Find a match
Option 1 - chemical phenomena, option 2 - physical:
- Melting paraffin
- Rotting plant residues
- Metal forging
- Burning alcohol
- Souring of fruit juice
- Dissolving sugar in water
- Blackening of copper wire during annealing
- Freezing water
- Milk souring
- Frost formation
IV. Introduction of knowledge.
1. Law of conservation of mass of substances.
Problematic question:Will the mass of the reactants change compared to the mass of the reaction products?
Demonstration experiments:
The teacher places two glasses on the scale:
A) one with freshly precipitated Cu(OH) 2 , the other with HCl solution; weighs them, pours the solutions into one glass, places another next to it, and the guys note that the balance of the scales has not been disturbed, although the reaction has passed, as evidenced by the dissolution of the precipitate;
b) The neutralization reaction is carried out similarly - excess acid from another glass is added to the phenolphthalein-colored alkali.
Video experiment:Heating copper.
Description of the experiment:Place 2 grams of crushed copper in a conical flask. Stopper the flask tightly and weigh. Remember the mass of the flask. Gently heat the flask for 5 minutes and observe the changes that occur. Stop heating and when the flask has cooled, weigh it. Compare the mass of the flask before heating with the mass of the flask after heating.
Conclusion: The mass of the flask did not change after heating.
Formulation law of conservation of mass:the mass of substances that reacted is equal to the mass of the formed substances(students write down the wording in their notebooks).
The law of conservation of mass was theoretically discovered in 1748 and experimentally confirmed in 1756 by the Russian scientist M.V. Lomonosov.
The French scientist Antoine Lavoisier in 1789 finally convinced the scientific world of the universality of this law. Both Lomonosov and Lavoisier used very precise scales in their experiments. They heated metals (lead, tin, and mercury) in sealed vessels and weighed the starting materials and reaction products.
Demonstration experiment:Heating a mixture of iron and sulfur.
Description of the experiment:In a mortar, prepare a mixture of 3.5 grams Fe and 2 grams S. Transfer this mixture to a porcelain cup and heat it strongly over a burner flame, observing the changes that occur. Apply a magnet to the resulting substance.
The resulting substance – iron (II) sulfide – is different from the original mixture. Neither iron nor sulfur can be visually detected in it. It is also impossible to separate them using a magnet. A chemical change has occurred.
The starting materials that take part in chemical reactions are called reagents.
New substances formed as a result of a chemical reaction are called products.
Let's write down the ongoing reaction in the form of a diagram:
iron + sulfur → iron(II) sulfide
Chemical equationis a conventional notation of a chemical reaction using chemical formulas.
Let's write the ongoing reaction in the form of a chemical equation:
Fe + S → FeS
Rules for composing chemical equations
(presentation on screen).
1. On the left side of the equation, write down the formulas of the substances that react (reagents). Then put the arrow.
a) N 2 + H 2 →
B) Al(OH) 3 →
B) Mg + HCl →
D) CaO + HNO 3 →
2. On the right side (after the arrow) write down the formulas of the substances formed as a result of the reaction (products). All formulas are compiled in accordance with the degree of oxidation.
a) N 2 + H 2 → NH 3
B) Al(OH) 3 → Al 2 O 3 + H 2 O
B) Mg + HCl → MgCl 2 + H 2
D) CaO + HNO 3 → Ca(NO 3 ) 2 + H 2 O
3. The reaction equation is drawn up based on the law of conservation of mass of substances, i.e. there must be the same number of atoms on the left and right. This is achieved by placing coefficients in front of the formulas of substances.
Algorithm for arranging coefficients in a chemical reaction equation.
2. Determine which element has a changing number of atoms, find the N.O.C.
3. Split N.O.C. for indices - get coefficients. Put coefficients in front of formulas.
5. It is better to start with O atoms or any other non-metal (unless O is part of several substances).
A) N 2 + 3H 2 → 2NH 3 b) 2Al(OH) 3 → Al 2 O 3 + 3H 2 O
B) Mg + 2HCl → MgCl 2 + H 2 g) CaO + 2HNO 3 → Ca(NO 3 ) 2 + H 2 O
V. Homework.§ 27 (up to types of reactions); No. 1 after §27
VI. Lesson summary. Students formulate conclusions about the lesson.
In lesson 11 "" from the course " Chemistry for dummies» we will find out by whom and when the law of conservation of mass of substances was discovered; Let's get acquainted with chemical equations and learn how to correctly place coefficients in them.
Until now, when considering chemical reactions, we paid attention to their high-quality side, i.e., on how and under what conditions the starting substances are converted into reaction products. But there is another side to chemical phenomena - quantitative.
Does the mass of substances that enter into a chemical reaction change? In search of an answer to this question, the English scientist R. Boyle back in the 17th century. conducted many experiments on calcination of lead in sealed vessels. After completing the experiments, he opened the vessels and weighed the reaction products. As a result, Boyle came to the conclusion that the mass of the substance after the reaction more mass source metal. He explained this by the addition of some “fiery matter” to the metal.
R. Boyle's experiments on calcination of metals were repeated by the Russian scientist M.V. Lomonosov in 1748. He calcined iron in a special flask (retort) (Fig. 56), which was hermetically sealed. Unlike Boyle, he left the retort sealed after the reaction. Weighing the retort after the reaction showed that its mass did not change. This indicated that although a chemical reaction had occurred between the metal and the substance contained in the air, the sum of the masses starting materials equal to the mass of the reaction product.
M.V. Lomonosov concluded: “ All changes that occur in nature are the essence of such a state that as much as something is taken away from one body, so much will be added to another, so if a little matter is lost somewhere, it will increase in another place».
In 1789, the French chemist A. Lavoisier proved that the calcination of metals is the process of their interaction with one of components air - oxygen. Based on the works of M.V. Lomonosov and A. Lavoisier, it was formulated law of conservation of mass of substances in chemical reactions.
The mass of substances that entered into a chemical reaction is equal to the mass of substances formed as a result of the reaction.
In chemical reactions, atoms do not disappear without a trace and do not appear out of nothing. Their number remains unchanged. And since they have constant mass , then the mass of the substances formed by them also remains constant.
The law of conservation of mass of substances can be verified experimentally. To do this, use the device shown in Figure 57, a, b. Its main part is a two-legged test tube. Pour lime water into one elbow, and the solution into the second. copper sulfate. Let's balance the device on the scales, and then mix both solutions in one elbow. At the same time, we will see that a blue precipitate of a new substance precipitates. The formation of a precipitate confirms that a chemical reaction has occurred. The mass of the device remains the same. This means that as a result of a chemical reaction, the mass of substances does not change.
The law is important for correct understanding everything that happens in nature: nothing can disappear without a trace and come from nothing.
Chemical reactions can be depicted using chemical formula language. Chemical elements are designated by chemical symbols, the composition of substances is written using chemical formulas, chemical reactions are expressed using chemical equations, i.e., just as words are made from letters, sentences are made from words.
Chemical reaction equation (chemical equation)- this is a conditional recording of a reaction using chemical formulasand the signs “+” and “=”.
The law of conservation of mass of substances in chemical reactions must also be observed when compiling chemical reaction equations. As in mathematical equations, in the equations of chemical reactions there is a left side (where the formulas of the starting substances are written) and a right side (where the formulas of the reaction products are written). For example (Fig. 58):
When writing equations of chemical reactions, the “+” (plus) sign connects the formulas of substances on the left and right parts equations Since the mass of substances before the reaction is equal to the mass of the formed substances, the “=” (equal) sign is used, which connects the left and right sides of the equation. To equalize the number of atoms on the left and right sides of the equation, numbers are used in front of the formulas of substances. These numbers are called coefficients of chemical equations and show the number of molecules or formula units. Since 1 mole of any substance consists of the same number structural units(6.02*10 23), then coefficients also show the chemical quantities of each substance:
When writing chemical equations, they also use special signs, for example, the sign “↓”, indicating that the substance forms a precipitate.
Law of conservation of mass of substances. CHEMICAL EQUATIONS
Chemistry teacher, MAOU "Secondary School No. 12", Kungur Perm region Foteeva V.A.
TEST
Option 2
1 option
to the physical?
A) boiling water
A) freezing of water
B) decomposition of water by electric current
B) combustion of sulfur
B) juice fermentation
C) quenching soda with vinegar
D) melting of metals
D) melting paraffin
D) food burning
D) evaporation of the salt solution
E) water distillation
E) food burning
G) filtering
G) extinguishing soda with vinegar
H) making tea
H) yellowing of leaves
Examination
Option 2
1 option
Which of the following phenomena are to the physical?
Which of the following phenomena are chemical (chemical reactions)?
A) boiling water
B) combustion of sulfur
B) juice fermentation
D) melting paraffin
D) food burning
D) evaporation of the salt solution
G) filtering
G) extinguishing soda with vinegar
H) making tea
H) yellowing of leaves
Let's remember!!!
- What is a chemical reaction?
- What signs of chemical reactions do you know?
- What do you think happens to substances? quantitative changes, for example what happens to mass substances?
- What will be the opinions?
- Opinions are divided. Which one of you is right?
What will be the topic of the lesson?
(What happens to a mass of substances during chemical reactions?)
- How can we find out?
- (Carry out the experiment, read in the textbook).
EXPERIENCE:
V closed system The substances that enter into the reaction are weighed: solutions of barium chloride (BaCl 2) and magnesium sulfate (MgSO 4) - m1, as well as the substances formed as a result of the reaction: barium sulfate (BaSO 4) and magnesium chloride (MgCl2) - m2.
- What phenomenon did you observe? Why do you think so?
- What happened to the mass of substances before and after the reaction?
- What is the smallest particle of matter?
- What particles are molecules made of? Remember the definition ATOM.
- What does it show chemical formula?
- How is it calculated molar mass, mass of matter?
- So Why but m1=m2?
- Can you answer immediately this question? Why? What do you need to know?
(Maybe know the chemical formulas - the composition of substances before and after the reaction and see how it changes whether atomic composition substances before and after the reaction?)
- What question arises?
(Does the atomic composition of substances change before and after the reaction?)
- What is the purpose of our lesson?
(Find out whether the quality and quantitative composition atoms in chemical reactions?)
Solving the problem
Let's write this reaction in Russian and then in chemical language:
barium chloride + magnesium sulfate barium sulfate + magnesium chloride
- 1atom Ba 1atom Mg 1atom Ba 1atom Mg
- 2 atoms Cl 1atom S 1atom S 2 atoms Cl
- 4 atoms O 4 atoms O
Before reaction After reaction
What conclusion can be drawn?
( Atoms and their composition before and after reaction have not changed )
- The results of weighing substances before and after the reaction confirm law conservation of mass substances. Students face a decision problematic task: why m1=m2? Thanks to the updating of previously acquired knowledge about the structure of substances, students relatively easily come to to the following conclusion: m1= m2, because atoms And their number as a result chemical transformations do not change, but only combine differently to form new substances.
Let's check our conclusion with calculations:
BaCl 2 + MgSO 4 Ba SO 4 + Mg Cl 2
Before the reaction - m1 After the reaction - m2
What did the calculations show?
What have you proven?
(m1= m2 ) Why?
Conservation Law
mass of matter
“All changes in nature that occur are of such a state that whatever is taken away from one body, the same amount is added to another. So, if matter decreases somewhere, it will increase in another place...”
Let's remember
Chemical formula – conventional recording of the composition of a substance using chemical symbols and indices.
Index shows the number of atoms in the formula unit of a substance.
Coefficient shows the number of particles not connected to each other
Chemical formula
Coefficient
Index
5H 2 ABOUT
Based on this law, equations are made chemical reactions
by using chemical formulas, coefficients and
mathematical signs.
Reaction equation
X A + at IN = With AB
A, B, AB - chemical formulas
x, y, s - odds
PHOSPHORUS + OXYGEN = PHOSPHORUS(V) OXIDE
1.P+O 2 P 2 +5 O 5 -2
2 . Let's start with oxygen.
3. O - 2 atoms on the left O- 5 atoms on the right
4. NOC = 10
5. 10: 2 = 5 P+ 5 O 2 P 2 O 5
6. 10: 5 = 2 P+5O 2 2 P 2 O 5
7. B left side equations must be placed before the phosphorus formula
coefficient – 4
4 P+ 5 O 2 = 2 P 2 O 5
Do the exercises:
1. Arrange the coefficients in a chemical reaction
Al+O 2 Al 2 O 3
2.Write the chemical reaction using chemical formulas and arrange the coefficients
iron(III) hydroxide + nitric acid iron (III) nitrate + water
Independent work.
Level 1:
Find and fix errors:
Al + 3HCl ═ AlCl 3 + 3H 2
Level 2:
Arrange the coefficients in the chemical reaction diagram:
FeSO 4 + KOH → Fe(OH) 2 +K 2 SO 4
Level 3:
Write an equation for the chemical reaction and arrange the coefficients:
Phosphorus (V) oxide + sodium hydroxide → sodium phosphate + water
Answers
Level 1:
2 Al+ 6 HCl═ 2 AlCl 3 + 3 H 2
Level 2:
FeSO 4 + 2 KOH ═ Fe(OH) 2 +K 2 SO 4
Level 3:
P 2 O 5 + 6 NaOH ═ 2 Na 3 P.O. 4 + 3 H 2 O
m2 "width="640" Like Boyle, the Russian scientist experimented in sealed retorts. But, unlike Boyle, Lomonosov weighed the vessels both before and after calcination without opening them. m1=m2
After two hours of heating, the sealed tip of the retort was opened, and outside air burst into it noisily.
According to our observation, this operation resulted in a gain of 8 grains in weight...” m1 m2
TEST YOURSELF
1).M.V. Lomonosov discovered the law of conservation of mass of substances in:
A.1789 B.1756 B.1673
2). Establish the correct sequence of the law of conservation of mass of substances:
A - mass of substances
B - mass of substances
B- as a result of her
G-reacted,
D-resulting
E- equal
3). The conventional notation for a chemical reaction is: A. chemical formula B. coefficient
B. chemical equation D. index
REFLECTION
Choose the expression that matches your work in the lesson:
1. Patience and work will grind everything down.
2. Hard to learn - easy to fight.
3. A bad soldier is one who does not dream of becoming a general.
4. The only way leading to knowledge is activity.
5. Any knowledge has value only when it makes us more energetic.
Homework
pp.96-98 § 27, ex.1(b), 2(d),3(b)
Let's remember!!!
- What phenomena are called chemical?
- What conditions are necessary for a chemical reaction to occur?
- By what signs can we judge that a chemical reaction has occurred?
- How did we denote the composition of a substance?
- Can you indicate the reaction? What is the topic and purpose of our lesson?
The law of conservation of mass is the basis for the calculation physical processes in all areas human activity. Its validity is not disputed by either physicists, chemists, or representatives of other sciences. This law, like a strict accountant, ensures that the exact mass of a substance is maintained before and after its interaction with other substances. The honor of discovering this law belongs to the Russian scientist M.V. Lomonosov.
Initial ideas about the composition of substances
The structure of matter remained a mystery to any person for many centuries. Various hypotheses excited the minds of scientists and encouraged the sages to engage in lengthy and meaningless debates. One argued that everything consists of fire, the other defended a completely different point of view. The theory of the ancient Greek sage Democritus that all substances consist of tiny, invisible to the eye, flashed through the mass of theories and was undeservedly forgotten. tiny particles substances. Democritus called them “atoms,” which means “indivisible.” Unfortunately, for as long as 23 centuries, his assumption was forgotten.
Alchemy
Basically, the scientific data of the Middle Ages were based on prejudices and various conjectures. Alchemy arose and spread widely, which was a body of modest practical knowledge, closely flavored with the most fantastic theories. For example, famous minds of that time tried to turn lead into gold and find the unknown philosopher's stone, healing from all diseases. During the search process, gradually accumulated scientific experience consisting of many unexplained reactions chemical elements. For example, it was found that many substances, later called simple, do not decay. Thus was reborn ancient theory about indivisible particles of matter. It took a great mind to turn this storehouse of information into a coherent and logical theory.
Lomonosov theory
Accurate quantitative method Chemistry research is indebted to the Russian scientist M.V. Lomonosov. For his brilliant abilities and hard work, he received the title of professor of chemistry and became a member Russian Academy Sci. Under him, the country's first modern chemical laboratory, in which the famous law of conservation of mass of substances was discovered.
In the process of studying the flow of chemical reactions, Lomonosov weighed the initial chemicals and products that appeared after the reaction. At the same time, he discovered and formulated the law of conservation of mass of matter. In the 17th century, the concept of mass was often confused with the term "weight". Therefore, masses of substances were often called “scales.” Lomonosov determined that the structure of a substance is directly dependent on the particles from which it is built. If it contains particles of the same type, then the scientist called such a substance simple. With a heterogeneous composition of corpuscles, it turns out compound. These theoretical data allowed Lomonosov to formulate the law of conservation of mass.
Definition of law
After numerous experiments, M.V. Lomonosov established a law, the essence of which boiled down to the following: the weight of substances that reacted, equal to weight substances resulting from the reaction.
In Russian science, this postulate is called “Lomonosov’s Law of Conservation of Mass of Substances.”
This law was formulated in 1748, and the most accurate experiments with the reaction of firing metals in sealed vessels were carried out in 1756.
Lavoisier's experiments
European science discovered the law of conservation of mass after the publication of a description of the works of the great French chemist Antoine Lavoisier.
This scientist boldly applied theoretical concepts and physical methods that time, which allowed him to develop chemical nomenclature and create a register of all chemical substances known at that time.
With his experiments, Lavoisier proved that in the process of any chemical reaction the law of conservation of mass of substances entering into a compound is observed. In addition, he expanded the extension of the law of conservation to the mass of each of the elements that took part in the reaction as part of complex substances.
Thus, the question of who discovered the law of conservation of mass of substances can be answered in two ways. M.V. Lomonosov was the first to conduct experiments that clearly demonstrated the conservation law and put it on a theoretical basis. A. Lavoisier in 1789, independently of the Russian scientist, independently discovered the law of conservation of mass and extended its principle to all elements participating in a chemical reaction.
Mass and energy
In 1905, the great A. Einstein showed the connection between the mass of a substance and its energy. It was expressed by the formula:
Einstein's equation confirms the law of conservation of mass and energy. This theory states that all energy has mass and a change in this energy causes a change in the mass of the body. The potential energy of any body is very high, and it can only be released under special conditions.
The law of conservation of mass is valid for any bodies of the micro- and macrocosm. Any chemical reaction takes part in the transformation of the internal energy of a substance. Therefore, when calculating the mass of substances participating in chemical reactions, it would be necessary to take into account the increase or loss of mass caused by the release or absorption of energy in a given reaction. In fact, in the macrocosm this effect is so insignificant that such changes can be ignored.
Task “Pyramid” Au MoMn CuCs Ag Mg Cr Md Al C Mt FFe ZSMV Below is a five-story pyramid, “ building stones» which are chemical elements. Find a path from its base to its top such that it contains only elements with constant valency. Law of conservation of mass of substances M.V. Lomonosov
Law of conservation of mass of substances 2 H 2 O 2H 2 + O 2 4H + 2O m1m1 m2m2 m3m3 m 1 = m 2 + m 3 Lavoisier (1789) Lomonosov Lomonosov (1756) We write the HR equations We solve problems using the HR equations = =36
Mikhail Vasilyevich Lomonosov (1711 – 1765) 1. Born in 1711 in Russia 2. Russian scientist - naturalist 3. Founder of the first Moscow University in Russia 4. Developed atomic-molecular ideas about the structure of substances 5. Discovered the law of conservation of mass of substances
Formulation of the law of conservation of mass of substances The mass of substances resulting from the reaction Law of conservation of mass of substances M.V. Lomonosova M.V. Lomonosov Consequence of the law Practical implementation The number of atoms of each element must be the same before and after the reaction. The mass of substances that entered into the reaction.
Algorithm for composing equations of chemical reactions 1. On the left side are written the formulas of the substances that react: KOH + CuCl On the right side (after the arrow) are the formulas of the substances that are obtained as a result of the reaction: KOH + CuCl 2 Cu(OH) 2 + KCl . 3. Then, using coefficients, the number of atoms of identical chemical elements on the right and left sides of the equation is equalized: 2KOH + CuCl 2 = Cu(OH) 2 + 2KCl.
Basic rules for arranging coefficients The arranging of coefficients begins with the element whose atoms participate in the reaction more. The number of oxygen atoms before and after the reaction should be even in most cases. If complex substances are involved in the reaction (exchange), then the arrangement of coefficients begins with metal atoms or acid residues.
H 2 O H 2 + O 2 Arrangement of coefficients in the chemical reaction equation 4 4: : 1 22 Coefficient
What does a chemical equation show? What substances react. What substances are formed as a result of the reaction. The mass of reactants and substances formed as a result of a chemical reaction. The ratio of the masses of reacting substances and substances formed as a result of a chemical reaction.
Lesson summary: What did we repeat in class today that you knew? What basic concepts did we remember? What new things did you learn today, what did you learn in class? What new concepts did we learn about in today's lesson? What do you think is your level of mastery of what you have learned? educational material? What questions caused the most difficulty?
Tasks 1. The mass of the flask in which the sulfur was burned did not change after the reaction. In which flask (open or closed) was the reaction carried out? 2. Balance the stub of a paraffin candle on the scales, then light it. How can the position of the scale change after some time? 3. When zinc weighing 65 g reacted with sulfur, zinc sulfide (ZnS) weighing 97 g was formed. What mass of sulfur reacted? 4. 9 g of aluminum and 127 g of iodine entered the reaction. What mass of aluminum iodide (Al I 3) is formed in this case?
The formula of water is H 2 O Calcium is a metal Phosphorus is a metal A complex substance consists of different substances The valency of hydrogen is I Melting sugar – chemical phenomenon Burning a candle is a chemical reaction. An atom is chemically divisible. Sulfur has a constant valence. Oxygen is a simple substance. sea water – pure substance Oil is a pure substance. A complex substance consists of different chemicals. elements Snow is a body Yes No Salt is a complex substance WITH UHR START FINISH Drawing up equations of chemical reactions
