Environment of the solution determination of the environment by the indicator. Determination of the nature of the medium of a solution of acids and alkalis using indicators

A lesson conducted using a notebook for practical work by I.I. Novoshinsky, N.S. Novoshinskaya to the textbook Chemistry Grade 8 in the MOU “Secondary School No. 11”, Severodvinsk, Arkhangelsk Region, by a chemistry teacher O.A. Olkina in grade 8 (on the parallel ).

The purpose of the lesson: Formation, consolidation and control of students' abilities to determine the reaction of the environment of solutions using various indicators, including natural ones, using a notebook for practical work by I.I. Novoshinsky, N.S. Novoshinskaya to the textbook Chemistry grade 8.

Lesson objectives:

1. Educational. To consolidate the following concepts: indicators, reaction of the medium (types), pH, filtrate, filtration based on the performance of practical work assignments. To check the knowledge of students, which reflect the relationship “solution of a substance (formula) - pH value (numerical value) - reaction of the environment”. Tell students about ways to reduce the acidity of soils in the Arkhangelsk region.
2. Developing. To promote the development of students' logical thinking based on the analysis of the results obtained in the course of practical work, their generalization, as well as the ability to draw a conclusion. Confirm the rule: practice proves the theory or refutes it. To continue the formation of the aesthetic qualities of the personality of students on the basis of a diverse range of solutions presented, as well as to support the interest of the children in the subject "Chemistry" being studied.
3. Nurturing. Continue to develop students' skills to perform practical work tasks, adhering to labor protection and safety rules, including correctly performing filtering and heating processes.

Practical work No. 6 “Determination of the pH of the medium”.

Purpose for students: Learn to determine the reaction of the environment of solutions of various objects (acids, alkalis, salts, soil solution, some solutions and juices), as well as to study plant objects as natural indicators.

Equipment and reagents: test tube rack, stopper, glass rod, ring rack, filter paper, scissors, chemical funnel, beakers, porcelain mortar and pestle, fine grater, clean sand, universal indicator paper, test solution, soil, boiled water, fruits, berries and other plant material, a solution of sodium hydroxide and sulfuric acid, sodium chloride.

During the classes

Guys! We have already got acquainted with such concepts as the reaction of the medium of aqueous solutions, as well as indicators.

What types of reactions in the environment of aqueous solutions do you know?

• neutral, alkaline and acid.

What are indicators?

• substances with which you can determine the reaction of the environment.

What indicators do you know?

• in solutions: phenolphthalein, litmus, methyl orange.

• dry: universal indicator paper, litmus paper, methyl orange paper

How can the reaction of an aqueous solution be determined?

• wet and dry.

What is the pH of the environment?

• pH value of hydrogen ions in solution (pH=– lg )

Let's remember which scientist introduced the concept of pH of the environment?

• Danish chemist Sorensen.

Well done!!! Now open the notebook for practical work on p.21 and read task number 1.

Task number 1. Determine the pH of the solution using a universal indicator.

Let's remember the rules when working with acids and alkalis!

Complete the experiment from task number 1.

Make a conclusion. Thus, if the solution has pH = 7, the medium is neutral, at pH< 7 среда кислотная, при pH >7 alkaline environment.

Task number 2. Get the soil solution and determine its pH using a universal indicator.

Read the task on p.21-p.22, complete the task according to the plan, put the results in the table.

Recall the safety rules when working with heating devices (alcohol).

What is filtering?

• the process of separating a mixture, which is based on the different throughput of the porous material - the filtrate in relation to the particles that make up the mixture.

What is a filtrate?

• it is a clear solution obtained after filtration.

Present the results in the form of a table.

What is the reaction of the soil solution medium?

• Sour

What needs to be done to improve soil quality in our region?

• CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2

Application of fertilizers that have an alkaline reaction of the environment: ground limestone and other carbonate minerals: chalk, dolomite. In the Pinezhsky district of the Arkhangelsk region there are deposits of such a mineral as limestone, near karst caves, so it is available.

Make a conclusion. The reaction of the environment of the resulting soil solution pH=4 is slightly acidic, therefore, liming is necessary to improve the quality of the soil.

Task number 3. Determine the pH of some solutions and juices using a universal indicator.

Read the task on p.22, complete the task according to the algorithm, put the results in the table.

juice source		juice source
Potato		silicate glue
fresh cabbage		table vinegar
Sauerkraut		Drinking soda solution
		Orange
		Fresh beets
		Boiled beets

Make a conclusion. Thus, different natural objects have different pH values: pH 1?7 – acidic environment (lemon, cranberry, orange, tomato, beet, kiwi, apple, banana, tea, potato, sauerkraut, coffee, silicate glue).

pH 7-14 alkaline environment (fresh cabbage, baking soda solution).

pH = 7 neutral medium (persimmon, cucumber, milk).

Task number 4. Study vegetable indicators.

What plant objects can act as indicators?

• berries: juices, flower petals: extracts, vegetable juices: root crops, leaves.
• substances that can change the color of the solution in different environments.

Read the task on p.23 and complete it according to the plan.

Record the results in a table.

Plant material (natural indicators)	Color of natural indicator solution
	Acid environment	Natural color of the solution (neutral medium)	Alkaline environment
Cranberry (juice)			Violet
Strawberries (juice)	orange	peach-pink
Blueberries (juice)		red-violet	blue - purple
Blackcurrant (juice)		red-violet	blue - purple

Make a conclusion. Thus, depending on the pH of the environment, natural indicators: cranberries (juice), strawberries (juice), blueberries (juice), black currants (juice) acquire the following colors: in an acidic environment - red and orange, in a neutral environment - red, peach - pink and violet colors, in an alkaline environment from pink through blue-violet to violet.

Consequently, the color intensity of the natural indicator can be judged by the reaction of the medium of a particular solution.

Tidy up your workspace when you're done.

Guys! Today was a very unusual lesson! Did you like?! Can the information learned in this lesson be used in everyday life?

Now complete the task that is given in your practice notebooks.

Task for control. Distribute the substances whose formulas are given below into groups depending on the pH of their solutions: HCl, H 2 O, H 2 SO 4, Ca (OH) 2, NaCl, NaOH, KNO 3, H 3 PO 4, KOH.

pH 17 - medium (acid), have solutions (HCl, H 3 PO 4, H 2 SO 4).

pH 714 medium (alkaline), have solutions (Ca (OH) 2, KOH, NaOH).

pH = 7 medium (neutral), have solutions (NaCl, H 2 O, KNO 3).

Evaluation for work _______________

Chemical properties of oxides: basic, amphoteric, acidic

Oxides are complex substances consisting of two chemical elements, one of which is oxygen with an oxidation state ($-2$).

The general formula for oxides is $E_(m)O_n$, where $m$ is the number of atoms of the element $E$ and $n$ is the number of oxygen atoms. oxides can be solid(sand $SiO_2$, varieties of quartz), liquid(hydrogen oxide $H_2O$), gaseous(carbon oxides: carbon dioxide $CO_2$ and carbon monoxide $CO$ gases). According to their chemical properties, oxides are divided into salt-forming and non-salt-forming.

Non-salt-forming such oxides are called that do not interact with either alkalis or acids and do not form salts. There are few of them, they include non-metals.

Salt-forming Oxides are called those that react with acids or bases and form salt and water.

Among the salt-forming oxides, oxides are distinguished basic, acidic, amphoteric.

Basic oxides are oxides that correspond to bases. For example: $CaO$ corresponds to $Ca(OH)_2, Na_2O to NaOH$.

Typical reactions of basic oxides:

1. Basic oxide + acid → salt + water (exchange reaction):

$CaO+2HNO_3=Ca(NO_3)_2+H_2O$.

2. Basic oxide + acid oxide → salt (compound reaction):

$MgO+SiO_2(→)↖(t)MgSiO_3$.

3. Basic oxide + water → alkali (compound reaction):

$K_2O+H_2O=2KOH$.

Acid oxides are oxides that correspond to acids. These are non-metal oxides:

N2O5 corresponds to $HNO_3, SO_3 - H_2SO_4, CO_2 - H_2CO_3, P_2O_5 - H_3PO_4$, as well as metal oxides with high oxidation states: $(Cr)↖(+6)O_3$ corresponds to $H_2CrO_4, (Mn_2)↖(+7 )O_7 - HMnO_4$.

Typical reactions of acidic oxides:

1. Acid oxide + base → salt + water (exchange reaction):

$SO_2+2NaOH=Na_2SO_3+H_2O$.

2. Acid oxide + basic oxide → salt (compound reaction):

$CaO+CO_2=CaCO_3$.

3. Acid oxide + water → acid (compound reaction):

$N_2O_5+H_2O=2HNO_3$.

Such a reaction is possible only if the acid oxide is soluble in water.

amphoteric called oxides, which, depending on the conditions, exhibit basic or acidic properties. These are $ZnO, Al_2O_3, Cr_2O_3, V_2O_5$. Amphoteric oxides do not combine directly with water.

Typical reactions of amphoteric oxides:

1. Amphoteric oxide + acid → salt + water (exchange reaction):

$ZnO+2HCl=ZnCl_2+H_2O$.

2. Amphoteric oxide + base → salt + water or complex compound:

$Al_2O_3+2NaOH+3H_2O(=2Na,)↙(\text"sodium tetrahydroxoaluminate")$

$Al_2O_3+2NaOH=(2NaAlO_2)↙(\text"sodium aluminate")+H_2O$.

Lesson topic: Creative tasks in GIA options

Place of the lesson: a generalizing lesson in grade 9 (in preparation for the GIA in chemistry).

Lesson duration: (60 min.).

Lesson content:

The lesson is structurally divided into 3 parts, corresponding to the questions in the GIA options.

Obtaining gaseous substances. Qualitative reactions to gaseous substances (oxygen, hydrogen, carbon dioxide, ammonia) (A 14).

Determination of the nature of the medium of a solution of acids and alkalis using indicators. Qualitative reactions to ions in solution (chloride, sulfate, carbonate ions, ammonium ion) (A 14).

Chemical properties of simple substances. Chemical properties of complex substances. Qualitative reactions to ions in solution (chloride, sulfate, carbonate ions, ammonium ion). Obtaining gaseous substances. Qualitative reactions to gaseous substances (oxygen, hydrogen, carbon dioxide) (C 3).

During the lesson, the teacher uses a multimedia presentation: "Creative tasks in the GIA options", "Safety in chemistry lessons", "Creative tasks in the GIA options" for the 3rd part of the lesson.

The purpose of the lesson: Prepare 9th grade students for the GIA in chemistry on specific issues.The purpose of the work: to consolidate knowledge about the properties of inorganic compounds of different classes, about qualitative reactions to ions.Deepen students' knowledge of chemistry, develop interest in the subject.

Lesson objectives :

- Deepen, systematize and consolidate,students' knowledge about the methods of obtaining, collecting and properties of various gases;

Develop the ability to analyze, compare, generalize, establish cause-and-effect relationships;

To acquaint with the methodology for completing tasks of GIA options on this topic;

Develop skills and abilities to work with chemical reagents and chemical equipment;

To promote the development of skills to apply knowledge in specific situations;

Expand the horizons of students, increase motivation for learning, socialization of students through independent activities;

Help students gain real experience in solving non-standard tasks;

Develop educational and communication skills;

To promote the development in children of the ability to exercise self-assessment and control of their activities;

Help students prepare for entry to secondary schools.

Tasks for students:

To get acquainted with the performance of creative tasks in the GIA variants (A-14, C3);

Learn to solve non-standard creative tasks;

To exercise control and self-control of their activities.

(Students read).

Lesson type:

Lesson for improving knowledge, skills and abilities (a lesson in the formation of skills and abilities, the targeted application of what was learned in the GIA variants)

lesson of generalization and systematization of knowledge;

combined.

Forms of work:

Frontal, group, individual, collective.

Methods and means of training:independent work of students, which they performed at home, in the classroom,individual work, group work, laboratory experience, blackboard work, using ICT, handouts and objects of the abstract world.

Lesson performance:

During the lesson, the teacher created conditions for the active activity of students, including creative ones.

Equipment: balloons, soap bubbles, individual cards, task cards, practical work assignments, homework cards, reflection sheet, test "How did I learn the material?",computer, projector, screen,presentations. Tables: solubilities, coloring of indicators, determination of ions. Tables at the blackboard.

Reagents: sodium carbonate, sodium chloride and sodium sulfate, hydrochloric acid, silver nitrate, barium chloride, calcium carbonate, water, ammonium chloride. Indicators: methyl orange, phenolphthalein, litmus).

Test "Our mood"

( Before the lesson, students are invited to take the squares of any color that the children want to take):

Red - energetic (attuned to work).

Yellow is the color of joy, good mood.

Blue is the color of calmness and balance.

Green - bored, but I hope this mood will change.

Brown - closed.

Black is gloomy.

Lesson motto: Goethe's words: “It is not enough to know, one must apply.

It’s not enough to want, you have to do it.”

During the classes:

Warm up:

Founder of the theory of electrolytic dissociation (Arrhenius).

The process by which an electrolyte breaks down into ions is called? (ED).

What substances are called electrolytes? (Substances whose aqueous solutions or melts conduct electric current).

Positively charged ions are called (cations).

Negatively charged ions are called (anions).

During the dissociation of alkalis, ions are formed (hydroxide ions).

List the conditions for the occurrence of ion exchange reactions (ion exchange reactions go to the end in three cases: 1. As a result of the reaction, a precipitate is formed; 2. a low-dissociating substance or water; 3. a gaseous substance is formed) (student answers).

Dissociation of acids produces ions (hydrogen ions).

First part of the lesson.

Obtaining gaseous substances. Qualitative reactions to gaseous substances (oxygen, hydrogen, carbon dioxide, ammonia)

Need to know:

Physical and chemical properties of gases (hydrogen, oxygen, carbon dioxide, ammonia).

Gas collection methods.

Name and operation of apparatus for obtaining gases

The main methods for obtaining gases in industry and laboratories

Gas identification ( qualitative reactions) .

1. Variety of gases. Distribute the gases you know into groups (individual work - students complete the task on separate sheets of paper, the answers are recorded on the screen, mutual verification is organized, students are rated).

The formulas of gaseous substances are printed on sheets and placed on the board in advance:

O 2 , CO, H 2 , NO 2 , CO 2 , N 2 , NH 3 , H 2 S, CI 2 , HCI.

1) gases are simple substances;

2) gases - oxides;

3) colored gases;

4) gases with a characteristic odor;

Answer: 1) Simple substances: N 2 , O 2 , H 2 , Cl 2 .

2) Oxides: CO, CO 2 , NO 2 .

3) Colored gases: Cl 2 , NO 2 .

4) Gases with a characteristic odor: Cl 2 , NO 2 , NH 3 , H 2 S, HCl.

2. Determine what gas the sphere is filled with. To do this: Calculate the air density of the gases given to you.

Balloons of different colors are hung on the board, located at different heights. Within 5 minutes, students must determine which gas from those whose formulas are listed below fills each balloon: NH 3 , CO 2 , N 2 , O 2 .

We create groups. Each group receives its own gas (a ball of a different color corresponding to the color of the cylinders in which liquefied gas is transported. For example, oxygen: a ball is blue), the properties of which the group will determine. 1 group - H 2 , group 2 - O 2 , group 3 - CO 2 , group 4 - NH 3 . Students also give an answer: why are the balls located at different heights?

3. Experience : Why do air bubbles fly down? (Water gun). Children give the answer.

Group work:

4. Name the physical properties of the gases given to you. Briefly. (Work in groups).

Oxygen-

Hydrogen -

Ammonia -

Carbon dioxide -

5. Answer the question: What methods of collecting gases do you know? Let's go to the slide:

Devices for collecting gases.

2) What gases can be collectedinstrument in figure 1 and 2?

Which are lighter than air 1, heavier - 2.

3) What gases can be collected by the device in figure 3?

Gases that are insoluble in water.

4) What device number will you collect

Group 1 - hydrogen? 2- oxygen?

O we are working on this issue according to the tasks of the GIA:

A) ammonia B) oxygen

C) carbon dioxide D) hydrogen sulfide

What gas is produced in the figure?

A) ammonia B) oxygen

C) carbon dioxide D) hydrogen

6 . We will work out laboratory and industrial methods for obtaining gases on GIA issues: (according to the handout, table 1.)

To what kind of gas do you get?

A) ammonia B) oxygen

C) carbon dioxide D) hydrogen

What kind of gas do you get?

A) ammonia

B) oxygen

B) carbon dioxide

D) hydrogen

What kind of gas do you get?

A) ammonia

B) oxygen

B) carbon dioxide

D) hydrogen

What kind of gas do you get?

A) ammonia B) oxygen C) carbon dioxide D) hydrogen

What kind of gas do you get?

A) ammonia B) oxygen

B) carbon dioxide D) hydrogen

7 .How to distinguish gases from each other?

What gas is determined?

A) ammonia B) oxygen

C) carbon dioxide D) hydrogen

What gas are the balloons filled with?

A) hydrogen sulfide B) oxygen

C) carbon dioxide D) hydrogen

What gas is poured?

A) ammonia B) oxygen

C) carbon dioxide D) hydrogen

A distinctive feature of tasks A14 2012 were questions on drawings.

Thus, in the tasks of the GIA there are the following questions on the drawings:

What gas is collected? (collection methods)

What kind of gas do you get? (Methods of obtaining)

What gas is determined? (Identification)

Presentation

2. The second part of the lesson.

Determination of the nature of the medium of a solution of acids and alkalis using indicators.

Qualitative reactions to ions in solution (chloride, sulfate, carbonate ions, ammonium ion.

Safety regulations (presentation).

1.Laboratory experience.

Safety in Chemistry Lessons (Multimedia Presentation)

In groups, identify the substances given to you.

Group 1

HCI), alkalis (NaOH) and water (H 2 O). Using the given substances (methylorange), determine in which test tube each of the substances is located.

Group 2

Group 3

Application 1.2 (for group 1-3)

Practical work No. 1

Lesson objectives:

Equipment: blackboard, chalk, table "Determining the nature of the medium of a solution of acids and alkalis using indicators", "Table of the solubility of acids, bases, salts in water", a tripod with test tubes, a spirit lamp, matches, a holder for test tubes.

Reagents: solutions: sodium hydroxide, hydrochloric acid, water, indicator - methyl orange.

Group 1

In three test tubes under numbers there are solutions: acids (HCI), alkalis (NaOH) and water (H 2 O). Using the given indicator substances (methyl orange, phenolphthalein, litmus), determine in which test tube each of the substances is located.

Instructions for work.

Task: in three numbered test tubes (1, 2, 3) substances are given: acids (HCI), alkalis (NaOH) and water (H 2 O).

With the help of characteristic reactions, recognize which of the test tubes contains these substances.

Run experiments 1, 2, 3.

Pour 2 - 3 ml of the solution into test tube No. 1 and add 1 - 2 drops of a solution of the indicator methyl orange, litmus, phenolphthalein, how did the color of the solution change?

Pour the indicator solution of methyl orange, litmus, phenolphthalein into test tube No. 2.

What are you watching?

Pour the indicator solution of methyl orange, litmus, phenolphthalein into test tube No. 3.

What are you watching?

3. Fill in the table.

Make the necessary entries in your notebook, voice the conclusion (One student from the group speaks). See handout Appendix 1.2.

Color change

in an acidic environment

Color change in an alkaline environment

Practical work No. 1

Topic: Qualitative reactions to ions.

The purpose of the work: using characteristic reactions to recognize inorganic substances.

Improve the skills of conducting a chemical experiment;

Confirm the conditions for carrying out ion exchange reactions in a practical way.

Lesson objectives:

Educational: with the help of a chemical experiment, consolidate the knowledge, skills and abilities of students in the section "Theory of electrolytic dissociation" (characteristic reactions to inorganic substances).

Developing: to promote the development of thinking (analyze, compare, highlight the main thing, establish cause-and-effect relationships), the development of cognitive interests.

Educational: to promote the formation of personality traits (responsibility, collectivism, initiative).

Type of lesson: application of knowledge, skills and abilities in practice.

Type of lesson: practical work.

Teaching methods: analytical, comparative, generalizing, classification.

Group 2

In three test tubes under numbers there are solutions: sodium carbonate, sodium chloride and sodium sulfate. Using the given substances (hydrochloric acid, silver nitrate, barium chloride), determine in which test tube each of the substances is located.

Instructions for work.

To perform this experiment, divide the contents of each numbered test tube into three samples.

Working process:

1. Table for recording the execution of work in the form:

2. Perform experiments 1, 2, 3.

What are you watching?

What are you watching?

What are you watching?

Write the reaction equation in molecular, full ionic, abbreviated ionic forms.

3. Fill in the table.

4. Draw a general conclusion. Record the results of the experimental part of the work in the report table. When compiling a report, use §§ 2,3,4.

Make the necessary entries

Practical work No. 1

Topic: Qualitative reactions to ions.

The purpose of the work: using characteristic reactions to recognize inorganic substances.

Improve the skills of conducting a chemical experiment;

Confirm the conditions for carrying out ion exchange reactions in a practical way.

Lesson objectives:

Educational: with the help of a chemical experiment, consolidate the knowledge, skills and abilities of students in the section: “Theory of electrolytic dissociation” (characteristic reactions to inorganic substances).

Developing: to promote the development of thinking (analyze, compare, highlight the main thing, establish cause-and-effect relationships), the development of cognitive interests.

Educational: to promote the formation of personality traits (responsibility, collectivism, initiative).

Type of lesson: application of knowledge, skills and abilities in practice.

Type of lesson: practical work.

Teaching methods: analytical, comparative, generalizing, classification.

Equipment: board, chalk, table of solubility of acids, bases, salts in water, stand with test tubes, spirit lamp, matches, test tube holder.

Reagents: solutions: hydrochloric acid, water, indicator - silver nitrate, calcium carbonate, sodium carbonate and sodium chloride, hydrochloric acid, ammonium chloride.

Group 3

Three numbered test tubes contain solids: calcium carbonate, ammonium chloride, and sodium chloride. Using the given substances (hydrochloric acid, silver nitrate, sodium hydroxide), determine in which test tube each of the substances is located.

Instructions for work.

To perform this experiment, divide the contents of each numbered test tube into three samples.

Working process:

1. Table for recording the performance of work in the form:

2. Perform experiments 1, 2, 3.

Pour a solution of silver nitrate into test tube No. 1.

What are you watching?

Write the reaction equation in molecular, full ionic, abbreviated ionic forms.

Pour hydrochloric acid solution into test tube No. 2.

What are you watching?

Write the reaction equation in molecular, full ionic, abbreviated ionic forms.

Pour sodium hydroxide solution into test tube No. 3.

What are you watching?

Write the reaction equation in molecular, full ionic, abbreviated ionic forms.

3. Fill in the table.

4. Draw a general conclusion. Record the results of the experimental part of the work in the report table. When compiling a report, use §§ 2,3,4.

Make the necessary entriesin a notebook, you voice the conclusion. (One student per group speaks). See handout Appendix 1.2.

3. The third part of the lesson

Chemical properties of simple substances. Chemical properties of complex substances.

Qualitative reactions to ions in solution (chloride, sulfate, carbonate ions, ammonium ion).

Obtaining gaseous substances.

Qualitative reactions to gaseous substances (oxygen, hydrogen, carbon dioxide, ammonia)

Creative tasks, task C 3, tasks are difficult.

3. Each group is invited to solve one combined problem. The group decides together. The solution is written on the board.

3.1 : Pavel Bazhov's fairy tale "The Mistress of the Copper Mountain" mentions a beautiful ornamental stone - malachite, from which vases, caskets, and jewelry are made. Chemical formula of malachite (CuOH) 2 CO 3 . During the thermal decomposition of malachite, three complex substances are formed: one solid black and two gaseous. When passing one of the resulting gaseous substances through lime water, its turbidity is observed due to the formation of a precipitate.

Write down the chemical formula and the name of the resulting precipitate. Write two molecular equations for the reactions that have been carried out.

Answer:t 0

(CuOH) 2 CO 3 → 2CuO + CO 2 + H 2 O

Malachite

CO 2 + Ca(OH) 2 → CaCO 3 ↓+H 2 O

This reaction is used to detect carbon monoxide (IV).

3.2: Substance X 1 obtained by reacting aluminum with a yellow powder. Under the action of water on X 1 poisonous gas with the smell of rotten eggs is released. This gas burns to form X 2 with a pungent odor. Define X 1 them 2. Write the equations for the reactions that take place. Specify the molar mass of substance X 2.

Answer:

2Al +3S → Al 2 S 3

Al 2 S 3 + 6 H 2 O→ 3H 2 S + 2Al(OH) 3

2 H 2 S + 3 O 2 → 2 SO 2 + 2H 2 O

Al 2 S 3 - X 1 , SO 2 - X 2 M (SO 2 ) = 64 g/mol

All experiments with hydrogen sulfide are carried out in a fume hood!

3.3: To determine the qualitative composition of a substance, students were given a metal salt, 1 kg of which in 1854 cost 270 times more than silver, and in the middleXXcentury has already been widely used for the manufacture of light metal structures. After dissolving the crystals of the issued salt in water, the students poured the resulting transparent solution into two test tubes.

A few drops of sodium hydroxide solution were added to one of them, and a gel-like white precipitate formed. A few drops of barium chloride solution were added to another test tube with a salt solution, and a white, milk-like precipitate formed.

Write down the chemical formula and name of the given salt. Make up two equations for the reactions that were carried out in the process of its recognition.

Answer:

Al 2 (SO 4 ) 3 +6NaOH→3Na 2 SO 4 +2Al(OH) 3 ↓ gelatinouswhitesediment

Al 2 ( SO 4 ) 3 + 3 BaCl 2 → 3 BaSO 4 ↓+ 2 AlCl 3

white, milky precipitate

Summing up the lesson. Reflection. Grading.

Evaluative-reflexive block

Let's analyze your work in groups. The floor is given to the leader of each group.

What questions did we cover in class today?

Which of these questions did you find the most difficult?

Test Annex 3

How did I get the material?

Homework (the task is printed out to each student)

Task number 1.

For the experiments, the researchers were given a substance that is water-insoluble yellow crystals. It is known that this substance is used in the manufacture of matches and the vulcanization of rubber. As a result of the interaction of the given substance with concentrated sulfuric acid, when heated, gaseous oxide and water are formed. And when the resulting oxide is passed through a solution of barium hydroxide, a white precipitate precipitates, which dissolves with further passing of the gas.

Write down the chemical formula and name the salt obtained as a result of the second experiment. Write two molecular reaction equations corresponding to the experiments conducted by the student during the study of salt.

t 0

S+2H 2 SO 4 = 3SO 2 + 2H 2 O

SO 2 + Ba(OH) 2 = BaSO 4 ↓+2H 2 O

barium sulfate

(At the end of the lesson, students who want to change the square to a square of a different color are invited to do so. Test "Our mood").

Appendix 1.

Table. Ion definition

reaction result

H +

Indicators

Color change

Ag+

Cl -

white sediment

Withu 2+

Oh -

S 2-

blue precipitate

Black sediment

Coloring the flame in blue-green color

Fe 2+

Oh -

Greenish precipitate that turns brown over time

Fe 3+

Oh -

Brown precipitate

Zn 2+

Oh -

S 2-

White precipitate, in excessOh - dissolves

white sediment

Al 3+

Oh -

A white jelly-like precipitate which, when in excessOh - dissolves

NH 4 +

Oh -

smell of ammonia

Ba 2+

SO 4 2-

white sediment

Coloring the flame in yellow-green color

Ca 2+

CO 3 2-

white sediment

Coloring the flame brick red

Na +

Flame color yellow

K +

Flame color purple (through cobalt glass)

Cl -

Ag +

white sediment

H 2 SO 4 *

Emission of a colorless gas with a pungent odorHCl)

Br -

Ag +

H 2 SO 4 *

Yellowish precipitate

SelectionSO 2 andBr 2 (brown color)

I -

Ag +

H 2 SO 4 +

yellow precipitate

SelectionH 2 SandI 2 (purple)

SO 3 2-

H +

SelectionSO 2 - a gas with a pungent odor that decolorizes a solution of magenta and violet ink

CO 3 2-

H +

Emission of an odorless gas that causes cloudy lime water

CH 3 COO -

H 2 SO 4

The smell of acetic acid

NO 3 -

H 2 SO 4 (conc.) andCu

Emission of brown gas

SO 4 2-

Ba 2+

white sediment

PO 4 3-

Ag +

yellow precipitate

Oh -

Indicators

Changing the color of indicators

Appendix 2

Practical work No. 1

Topic: Qualitative reactions to ions.

The purpose of the work: using characteristic reactions to recognize inorganic substances.

Improve the skills of conducting a chemical experiment;

Confirm the conditions for carrying out ion exchange reactions in a practical way.

Lesson objectives:

Educational: with the help of a chemical experiment, consolidate the knowledge, skills and abilities of students in the section "Theory of electrolytic dissociation" (characteristic reactions to inorganic substances).

Developing: to promote the development of thinking (analyze, compare, highlight the main thing, establish cause-and-effect relationships), the development of cognitive interests.

Educational: to promote the formation of personality traits (responsibility, collectivism, initiative).

Type of lesson: application of knowledge, skills and abilities in practice.

Type of lesson: practical work.

Teaching methods: analytical, comparative, generalizing, classification.

Equipment: board, chalk, table of solubility of acids, bases, salts in water, stand with test tubes, spirit lamp, matches, test tube holder.

Reagents: sodium carbonate, sodium chloride and sodium sulfate, hydrochloric acid, silver nitrate, barium chloride.

Group 2

In three test tubes under numbers there are solutions: sodium carbonate, sodium chloride and sodium sulfate. Using the given substances (hydrochloric acid, silver nitrate, barium chloride), determine in which test tube each of the substances is located.

Instructions for work.

To perform this experiment, divide the contents of each numbered test tube into three samples.

Working process:

1. Table for recording the execution of work in the form:

2. Perform experiments 1, 2, 3.

Pour a solution of barium chloride into test tube No. 1.

What are you watching?

Write the reaction equation in molecular, full ionic, abbreviated ionic forms

Pour hydrochloric acid solution into test tube No. 2.

What are you watching?

Write the reaction equation in molecular, full ionic, abbreviated ionic forms.

Pour a solution of silver nitrate into test tube No. 3.

What are you watching?

Write the reaction equation in molecular, full ionic, abbreviated ionic forms.

3. Fill in the table.

4. Draw a general conclusion. Record the results of the experimental part of the work in the report table. When compiling a report, use §§ 2,3,4.

Make the necessary entries in a notebook, you voice the conclusion. (One student per group speaks).

Application3

Test

How did I get the material?

1. Received solid knowledge, mastered all the material 9-10 points

2. Learned the material partially 7-8 points

3. I didn’t understand much, I still need to work 4-6 points

4. How would you rate yourself for participating in the work of the groups? (Rate yourself here).

Depending on which H + or OH - ions are in excess in an aqueous solution, the following types (characters) of solution media are distinguished:

1) sour

2) alkaline

3) neutral

At acidic nature of the environment the solution contains an excess of hydrogen cations H + , and the concentration of hydroxide ions is close to zero.

At alkaline environment there is an excess of hydroxide ions OH - in the solution, and the concentration of H + cations is close to zero.

At neutral environment solution, the concentrations of H + and OH ions are equal to each other and practically equal to zero (0.0000001 mol / l).

There are some organic substances, the color of which changes depending on the nature of the environment. This phenomenon is widely used in chemistry. Some of the most common indicators are litmus, phenolphthalein, and methyl orange (methyl orange). What color these substances have, depending on the nature of the medium, is presented in the following table:

	indicator color
indicator	in a neutral environment	in an acidic environment	in an alkaline environment
litmus	Violet	red	blue
phenolphthalein	colorless	colorless	crimson
methyl orange (methyl orange)	orange	pink	yellow

As you can see, a specific property of phenolphthalein is that this indicator does not make it possible to distinguish between neutral and acidic environments - in both environments it is not colored in any way. This property is undoubtedly a disadvantage, however, phenolphthalein is widely used due to its exceptional sensitivity to even a slight excess of OH - ions.

Obviously, with the help of indicators, acids, alkalis and distilled water can be distinguished from each other. However, it should be remembered that acidic, alkaline and neutral media can be observed not only in solutions of acids, alkalis and distilled water. The solution environment can also be different in salt solutions depending on their relationship to hydrolysis.

So, for example, a solution of sodium sulfite from a solution of sodium sulfate can be distinguished using phenolphthalein. Sodium sulfite is a salt formed by a strong base and a weak acid, so its solutions will have an alkaline environment. Phenolphthalein will turn crimson in its solution. Sodium sulfate, on the other hand, is formed by a strong base and a strong acid, i.e. does not undergo hydrolysis, and its aqueous solutions will have a neutral reaction of the environment. In the case of sodium sulfate solution, phenolphthalein will remain colorless.

Chemically, the pH of a solution can be determined using acid-base indicators.

Acid-base indicators are organic substances whose color depends on the acidity of the medium.

The most common indicators are litmus, methyl orange, phenolphthalein. Litmus turns red in an acidic environment and blue in an alkaline environment. Phenolphthalein is colorless in an acidic medium, but turns crimson in an alkaline medium. Methyl orange turns red in an acidic environment and yellow in an alkaline environment.

In laboratory practice, a number of indicators are often mixed, selected in such a way that the color of the mixture varies over a wide range of pH values. With their help, you can determine the pH of the solution with an accuracy of up to one. These mixtures are called universal indicators.

There are special devices - pH meters, with which you can determine the pH of solutions in the range from 0 to 14 with an accuracy of 0.01 pH units.

Salt hydrolysis

When some salts are dissolved in water, the equilibrium of the water dissociation process is disturbed and, accordingly, the pH of the medium changes. This is because salts react with water.

Salt hydrolysis – chemical exchange interaction of dissolved salt ions with water, leading to the formation of weakly dissociating products (molecules of weak acids or bases, anions of acid salts or cations of basic salts) and accompanied by a change in the pH of the medium.

Consider the process of hydrolysis, depending on the nature of the bases and acids that form the salt.

Salts formed by strong acids and strong bases (NaCl, kno3, Na2so4, etc.).

Let's say that when sodium chloride reacts with water, a hydrolysis reaction occurs with the formation of an acid and a base:

NaCl + H 2 O ↔ NaOH + HCl

For a correct understanding of the nature of this interaction, we write the reaction equation in ionic form, taking into account that the only weakly dissociating compound in this system is water:

Na + + Cl - + HOH ↔ Na + + OH - + H + + Cl -

With the reduction of identical ions, the water dissociation equation remains on the left and right sides of the equation:

H 2 O ↔ H + + OH -

As can be seen, there are no excess H + or OH - ions in the solution compared to their content in water. In addition, no other weakly dissociating or hardly soluble compounds are formed. Hence we conclude that salts formed by strong acids and bases do not undergo hydrolysis, and the reaction of solutions of these salts is the same as in water, neutral (pH = 7).

When compiling ion-molecular equations for hydrolysis reactions, it is necessary:

1) write down the salt dissociation equation;

2) determine the nature of the cation and anion (find the cation of a weak base or the anion of a weak acid);

3) write down the ion-molecular reaction equation, given that water is a weak electrolyte and that the sum of the charges must be the same in both parts of the equation.

Salts formed from a weak acid and a strong base

(Na 2 CO 3 , K 2 S, CH 3 COONa and others .)

Consider the hydrolysis reaction of sodium acetate. This salt in solution decomposes into ions: CH 3 COONa ↔ CH 3 COO - + Na + ;

Na + is a cation of a strong base, CH 3 COO - is an anion of a weak acid.

Na + cations cannot bind water ions, since NaOH, a strong base, completely decomposes into ions. Anions of weak acetic acid CH 3 COO - bind hydrogen ions to form slightly dissociated acetic acid:

CH 3 COO - + HOH ↔ CH 3 COOH + OH -

It can be seen that, as a result of the hydrolysis of CH 3 COONa, an excess of hydroxide ions formed in the solution, and the reaction of the medium became alkaline (рН > 7).

Thus, it can be concluded that salts formed by a weak acid and a strong base are hydrolyzed at the anion ( An n - ). In this case, salt anions bind H ions + , and OH ions accumulate in the solution - , which causes an alkaline environment (pH> 7):

An n - + HOH ↔ Han (n -1) - + OH -, (at n = 1, HAn is formed - a weak acid).

Hydrolysis of salts formed by dibasic and tribasic weak acids and strong bases proceeds stepwise

Consider the hydrolysis of potassium sulfide. K 2 S dissociates in solution:

K 2 S ↔ 2K + + S 2-;

K + is a cation of a strong base, S 2 is an anion of a weak acid.

Potassium cations do not take part in the hydrolysis reaction; only anions of weak hydrosulphuric acid interact with water. In this reaction, weakly dissociating HS - ions are formed in the first stage, and weak acid H 2 S is formed in the second stage:

1st stage: S 2- + HOH ↔ HS - + OH -;

2nd stage: HS - + HOH ↔ H 2 S + OH -.

The OH ions formed in the first stage of hydrolysis significantly reduce the likelihood of hydrolysis in the next stage. As a result, the process that proceeds only through the first stage is usually of practical importance, which, as a rule, is limited when assessing the hydrolysis of salts under normal conditions.