MBOU secondary school No. 139 of the city district of Samara.
Synopsis of a lesson in chemistry for grade 8.
Topic: Chemical formulas. Relative atomic and molecular masses. Mass fraction element in the connection.
Lesson Objectives
educational:
- to study the concepts: chemical formula, index, coefficient; writing and reading formulas.
- to study the differences between relative, atomic and molecular masses;
– will study the concept of mass fraction chemical element and learn how to calculate it.
developing:
- to develop in students the ability to make simple, logical constructions based on chemical knowledge;
- develop the ability to use in non-standard situations research activities knowledge from various sections of school disciplines (physics, algebra), if necessary, find the missing information in the reference and educational literature;
educational:
- to cultivate personal reflection, that is, the ability to comprehend one's actions and oneself in a problematic research situation;
- to cultivate self-organization and self-esteem of students in the performance of research tasks in the classroom.
Equipment: tables "Relative atomic and molecular masses", individual cards assignments for students, the table of D.I. Mendeleev.
During the classes
The teacher sets up the students to work during the lesson. Explains all the stages of the lesson and the actions of students at each of them.
- Guys today, each of you will become a researcher and will "obtain new knowledge": find out the composition of chemical formulas, the rules for writing and reading them; derive the formula for the mass fraction of a chemical element and calculate it.
II. Study of new topic
1. The word of the teacher.
- Each atom of any chemical element has its own mass, as well as any physical body that surrounds us, including you and me. But unlike us, the mass of atoms is very small. Therefore, scientists have taken as a standard the mass 1/12 the mass of a carbon atom 6 12 FROM(as the lightest) and the mass of the remaining atoms was compared with the mass of this standard, hence the name "Relative atomic mass" from the English. « relative » relative. This value has no units and is denoted Ar . The numerical value of the relative atomic mass of any element is written in periodic table DI. Mendeleev.
If a substance is formed by several elements (the same or different), then we are talking about molecules and the “Molecular Relative Mass”. She develops from atomic masses all chemical elements that make up a molecule multiplied to the number of these atoms. It also has no units of measurement and is denoted Mr . For example:
Mr (O 2) \u003d Ar (O) 2 \u003d 16 2 \u003d 32;
Mr (H 2 O) \u003d Ar (H) 2 + Ar (O) \u003d 1 2 + 16 \u003d 18;
Mr (H 2 SO 4) \u003d Ar (H) 2 + Ar (S) + Ar (O) 4 \u003d 1 2 + 32 + 16 4 \u003d 98;
The teacher repeatedly reminds the students that the value of Ar is found in periodic system DI. Mendeleev under the sign of a chemical element. The value of the atomic masses of different chemical elements are added together. If there are several identical atoms in a molecule, from them numerical value atomic masses is multiplied by the number of those atoms. (consolidation of the new topic will occur when doing independent work in the research part of the lesson)
2. Research part (independent work students under the guidance of a teacher), if students have difficulties, the teacher must be very careful and in no case give the students a direct correct answer, that is, " ready knowledge“They have to get them themselves. It is better to “push” the student to the correct solution with leading questions that stimulate mental activity, the need to connect existing knowledge from other areas with new material. This is necessary in order not to disrupt the process of students' research and to achieve the best result when studying new material, since knowledge acquired independently is retained in long-term memory than ready-made information.
Sample questions:
- How do you think?
“Imagine what would happen if…?”
— How will it change and what does it mean?
— Think about where else you met with this concept? etc.
The teacher gives the students cards - tasks, focuses their attention on the fact that this is an independent research, but if necessary, you (the teacher) will definitely help and direct the work of each student in the right direction.
Cards - tasks
Topic: Chemical formula. Relative, atomic and molecular masses. Mass fraction of chemical elements.
Task 1. Chemical formula, its composition, recording and pronunciation.
BUT. Explore the qualitative and quantitative composition of chemical formulas. Analyze what each of them means in the formula.
Qualitative composition | |
O 3 | oxygen ( O) |
H 2 | hydrogen ( H) |
Al 2 O 3 | aluminum ( Al) and oxygen (O) |
Conclusions:
1) Qualitative composition The chemical formula shows: ____________________________________ form a substance.
2) Quantitative composition chemical formula shows:
They form a substance.
IN. Analyze the entry, what do you think the index and coefficient in the chemical formula shows.
2
Al 2
O 3
coefficient index
index - this is _____________, which shows _______________ in a substance, it is written ______________________ of the symbol of a chemical element;
coefficient is _______________, which shows the number of _____________ chemical, is written ______________ chemical formula;
IN. Explore the rules for reading formulas.
The order of pronunciation of the components of the formula:
1. coefficient
2. chemical element symbol * and its index (if any.)
3. the next symbol of a chemical element and its index.
* when reading a chemical formula, the pronunciation of the symbol of the chemical element is read, and not its name.
Independent work.
(consolidation of new material)
1.1. write down qualitative composition each formula:
H 2 SO 4 _______________ FeSO 3 _____________________
H 3 PO 4 ________________ H 2 Cl 2 O 7 ____________________
1.2. Write down the quantitative composition of each formula:
O 3 __________________ K 2 O _______________________
Cl 2 __________________ MgCO 3 ____________________
MgO ________________ NaOH _____________________
H 2 SO 4 _______________ FeSO 3 _____________________
H 3 PO 4 ________________ H 2 Cl 2 O 7 ____________________
1.3. Read the formulas. Write down what you got:
Li 2 O _________________________________________________
CAS ___________________________________________________
H 2 SiO 3 _________________________________________________
MgSO4 _________________________________________________
Task 2. Dependence of the mass fraction of elements in a compound on some physical quantities.
Analyze on what parameters and how the mass fraction of an element in a compound depends.
BUT. Explore the composition and relative atomic masses of the elements of the HCl molecule.
Composition | qualitative | hydrogen H | chlorine Cl |
quantitative | |||
Relative atomic mass of Ar | |||
Compare the mass fractions of elements in the compound: (H) _________ (Cl)
( , , )
B. Explore the composition of ethane C 2 H 6 and acetylene C 2 H 2 molecules.
ethane C 2 H 6 |
acetylene C 2 H 2 | |
Number of atoms carbon n(C) | ||
Number of atoms hydrogen n(H) |
Compare mass fractions hydrogen in ethane and acetylene:
( H) C 2 H 6 _______________ (H) C 2 H 2
( , , )
What parameter and how does it affect the value of the mass fraction of an element in a compound?
IN. Explore the composition of the molecule of carbon dioxide CO 2 and carbon monoxide CO .
carbon dioxide CO2 |
carbon monoxide CO | |
Number of carbons n (C) | ||
Relative molecular weight of the compound Mr |
Compare the mass fractions of carbon in carbon dioxide and carbon monoxide:
( C) CO 2 _____________ (C) CO
( , , )
What parameter and how does it affect the value of the mass fraction of an element in a compound?
Generalize the findings and make a formula showing the dependence of the mass fraction on the parameters you found. For this: Write inversely proportional to the denominator
the value of the mass fraction
To express the mass fraction as a percentage, it is necessary to multiply the right side of the formula by 100%
Independent work.
2.1. Underline the compound in which the largest mass fraction of sulfur is:
but ) Na 2 SO 3 and Na 2 S 2 O 3; b) H 2 S and Na 2 S; c) Na 2 S 4 O 6 and Na 2 S 2 O 8.
2.2. Without making calculations, write the following compounds in a row in order of decreasing mass fraction:
a) hydrogen - H 2 O, H 2 O 2 _________________________
b) chlorine - Cl 2 O, Cl 2 O 7, ClO 2 ______________________
c) sulfur - SCl 4, S 2 Cl 2, SCl 2 ________________________
d) carbon - CH 4, C 2 H 2, C 2 H 4 ____________________
e) fluorine - P 2 F 4 , PF 3 , PF 5 _________________________
III. Lesson results.
The results are summed up, the chemical concepts studied in this lesson are spoken out: relative atomic and molecular masses, chemical formula, index, coefficient, mass fraction of a chemical element in a compound.
IV. Homework.
§five. ex. 1-5. (which of the students did not complete independent tasks during the lesson, do them at home)
Obernikhina Tatyana Sergeevna
high school chemistry teacher categories.
MOU "Secondary School No. 3 of Koryazhma"
Subject . Chemistry.
Lesson topic Mass fraction of the element.
8TH GRADE.
WMC G.E. Rudzitis.
Lesson type: Learning new material
Target : To form the skill of solving problems for calculating the proportion and finding the mass of the component of the solution.
Tasks
Educational:
Form the concept of the mass fraction of an element;
To teach the establishment of the simplest formula of a substance by the mass fractions of elements.
Developing:
To develop logical thinking skills and students' interest in chemical science.
Educational:
To educate a person with an ecological way of thinking.
To instill in students a sense of camaraderie and responsibility.
Planned learning outcomes:
subject:
formation of systematized knowledge about the proportion of an element in a substance;
development of the ability to calculate the mass fraction in various substances;
metasubject:
formation of competence in the field of using the acquired knowledge on others academic disciplines;
personal:
formation of conviction in the need for chemical knowledge for human life;
Means of education :
Multimedia projector;
A computer;
Cards;
The flyleaf of the textbook with the table of D.I. Mendeleev;
Notebooks;
Table by D.I. Mendeleev;
Epigraph to the lesson:
Nature surrounds us with mysteries and, and
an attempt to solve them belongs
to the greatest joys of life.
W. Ramsay
Lesson stages
| Lesson stage | Teacher activity | Student activities |
| 1. Organizational moment. | Checks the readiness of children for the lesson. Greetings, positive attitude to the lesson. | Check readiness for the lesson. |
| 2. Goal setting and motivation. | Creating a stimulating and motivating situation through a system of questions: Here are the various minerals from which iron can be obtained. (FeO, Fe2 O3 , Fe3 O4 ) (on multimedia projector). Problematic question: What do you think is the most profitable mineral to use for iron production. | Put forward their assumptions on the question posed. |
| Organizes the activities of students to formulate the topic and objectives of the lesson. What do you think is the purpose of our lesson? | Determine the purpose of the lesson |
|
| You have a certain amount of knowledge, what concepts learned earlier will help you achieve your goal? | Chemical element, chemical formula, relative atomic and molecular mass. |
|
| 3.Updating and control of knowledge. | What can we say about these minerals? | Composed of iron and oxygen atoms |
| Is it possible to answer the question posed qualitatively and quantitatively? | Teamwork |
|
| Molecular weight of substances |
||
| Examination homework | On the cards issued, students calculate the molar mass of iron oxides. After completing the task, they exchange cards with a neighbor on their desk and check them together with the teacher. |
|
| 3. The study of new educational material. | Organizes a conversation using the presentation information, the text of the textbook and the workbook. Controls the "discovery" of new knowledge. Corrects them. How can you graphically represent the written formulas? What is a share? Draws an analogy of calculating the proportion of a substance with mathematics. What is the main quantity in chemistry What is the atomic mass of iron? How, based on the knowledge of atomic and molecular weight, can one derive the formula of a substance? Calculate the mass fraction of iron in each substance and answer the question (return to the first slide) Discussion of completed tasks. Does the mining process affect environment? Fizkultminutka. Let's remember the chemical elements. I call you the name, if it matches the pronunciation - raise right hand if not, left. Generalization and systematization Introduces new substances in which the same chemical element occurs. Calculate its mass fraction in each. SO2 and SO3 ω(S) = SO2 and CO ω (C) = ω (N) = HNO3 , HNO2 Complete the tasks in the workbook to consolidate the material. | Answer the questions provided. Draw the composition of substances in different colors. Part of the whole. Students remember how proportion is calculated in mathematics. Atomic mass element Together with the teacher, derive the formula of the substance ω=(Ar n/Mr) 100% Calculate. 3 students work at the blackboard Answer the question Put forward their assumptions Fizkultminutka. One of the students in the direction of the teacher - calls the correct pronunciation. Make calculations They do the job. |
| 4. Reflection and summing up the lesson. | Organizes reflection and summing up the lesson. If your mom asked you to write her an SMS about the most important thing in the lesson, what would you write? Have we achieved our goals? Guys, finishing the lesson, I ask you to stick the issued circle on one of the posters at the exit. (Everything was learned, not enough learned, serious revision is required). | They speak their answers. Evaluate their work in posters at the exit. |
| 5.Information about homework. | Offers a task in accordance with the possibilities: 1. Calculate in which of the proposed compounds (hydrogen peroxide, water, sulphuric acid, calcium oxide, sodium peroxide-formulas written down by the teacher) is the mass fraction of oxygen the largest? 2. Find the mass fraction of each element in the compound(Fe3 (PO4 ) 2 *8H2 O) | They make a choice of homework in accordance with their own abilities and abilities, and their interest in the topic studied. |
Literature used:
1. Chemistry, grade 8, Inorganic chemistry, Grade 8, Rudzitis G.E., Feldman F.G., 2013.
2. Fadeev G.N. Tasks and tests for self-training in chemistry: a guide for students and teachers. - M.: BINOM. Knowledge Lab, 2008.
3. Workbook. 8th grade.
4. Didactic materials. 8-9 grades.
Knowing chemical formula, you can calculate the mass fraction of chemical elements in a substance. element in substances is denoted by the Greek. the letter "omega" - ω E / V and is calculated by the formula:
where k is the number of atoms of this element in the molecule.
What is the mass fraction of hydrogen and oxygen in water (H 2 O)?
Solution:
M r (H 2 O) \u003d 2 * A r (H) + 1 * A r (O) \u003d 2 * 1 + 1 * 16 \u003d 18
2) Calculate the mass fraction of hydrogen in water:
3) Calculate the mass fraction of oxygen in water. Since the composition of water includes atoms of only two chemical elements, the mass fraction of oxygen will be equal to:
Rice. 1. Formulation of the solution of problem 1
Calculate the mass fraction of elements in the substance H 3 PO 4.
1) Calculate the relative molecular weight substances:
M r (H 3 RO 4) \u003d 3 * A r (H) + 1 * A r (P) + 4 * A r (O) \u003d 3 * 1 + 1 * 31 + 4 * 16 \u003d 98
2) We calculate the mass fraction of hydrogen in the substance:
3) Calculate the mass fraction of phosphorus in the substance:
4) Calculate the mass fraction of oxygen in the substance:
1. Collection of tasks and exercises in chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. "Chemistry, Grade 8" / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. - M.: AST: Astrel, 2006.
2. Ushakova O.V. Chemistry workbook: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. Grade 8” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M .: AST: Astrel: Profizdat, 2006. (p. 34-36)
3. Chemistry: 8th grade: textbook. for general institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005.(§15)
4. Encyclopedia for children. Volume 17. Chemistry / Chapter. edited by V.A. Volodin, leading. scientific ed. I. Leenson. - M.: Avanta +, 2003.
1. A single collection of digital educational resources ().
2. Electronic version of the journal "Chemistry and Life" ().
4. Video lesson on the topic "Mass fraction of a chemical element in a substance" ().
Homework
1. p.78 No. 2 from the textbook "Chemistry: 8th grade" (P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M .: AST: Astrel, 2005).
2. from. 34-36 №№ 3.5 from the Workbook in Chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. Grade 8” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006.
