Dissolution. Solubility of substances in water. Solubility of solids in water I Dissolution and solutions
Solutions play a key role in nature, science and technology. Water is the basis of life, always contains dissolved substances. Fresh water of rivers and lakes contains few dissolved substances, while sea water contains about 3.5% of dissolved salts.
The primordial ocean (during the birth of life on Earth) is thought to have contained only 1% dissolved salts.
“It was in this environment that living organisms first developed, from this solution they scooped up the ions and molecules that are necessary for their further growth and development ... Over time, living organisms developed and transformed, so they were able to leave the aquatic environment and move to land and then rise to air. They obtained these abilities by preserving in their organisms an aqueous solution in the form of liquids that contain a vital supply of ions and molecules, ”the famous American chemist, Nobel Prize winner Linus Pauling describes the role of solutions in nature in these words. Inside each of us, in every cell of our body, there are memories of the primordial ocean, the place where life originated, an aqueous solution that provides life itself.
In any living organism, an unusual solution constantly flows through the vessels - arteries, veins and capillaries, which forms the basis of blood, the mass fraction of salts in it is the same as in the primary ocean - 0.9%. Complex physicochemical processes occurring in the human and animal body also interact in solutions. The process of assimilation of food is associated with the transfer of highly nutritious substances into solution. Natural aqueous solutions are directly related to the processes of soil formation, the supply of plants with nutrients. Such technological processes in the chemical and many other industries, such as the production of fertilizers, metals, acids, paper, occur in solutions. Modern science deals with the study of the properties of solutions. Let's find out what is a solution?
Solutions differ from other mixtures in that the particles of the constituents are evenly distributed in them, and in any microvolume of such a mixture the composition will be the same.
That is why solutions were understood as homogeneous mixtures, which consist of two or more homogeneous parts. This idea was based on the physical theory of solutions.
Adherents of the physical theory of solutions, which van't Hoff, Arrhenius and Ostwald were engaged in, believed that the dissolution process is the result of diffusion.
D. I. Mendeleev and supporters of the chemical theory believed that dissolution is the result of the chemical interaction of a solute with water molecules. Thus, it will be more accurate to define a solution as a homogeneous system that consists of particles of a solute, a solvent, and also the products of their interaction.
Due to the chemical interaction of a solute with water, compounds are formed - hydrates. Chemical interaction is usually accompanied by thermal phenomena. For example, the dissolution of sulfuric acid in water takes place with the release of such an enormous amount of heat that the solution can boil, which is why acid is poured into water, and not vice versa. The dissolution of substances such as sodium chloride, ammonium nitrate, accompanied by the absorption of heat.
M. V. Lomonosov proved that solutions turn into ice at a lower temperature than the solvent.
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Solution is called a thermodynamically stable homogeneous (single-phase) system of variable composition, consisting of two or more components (chemicals). The components that make up a solution are a solvent and a solute. Typically, a solvent is considered to be a component that exists in its pure form in the same state of aggregation as the resulting solution (for example, in the case of an aqueous salt solution, the solvent is, of course, water). If both components before dissolution were in the same state of aggregation (for example, alcohol and water), then the component that is in a larger amount is considered the solvent.
Solutions are liquid, solid and gaseous.
Liquid solutions are solutions of salts, sugar, alcohol in water. Liquid solutions may be aqueous or non-aqueous. Aqueous solutions are solutions in which the solvent is water. Non-aqueous solutions are solutions in which organic liquids (benzene, alcohol, ether, etc.) are solvents. Solid solutions are metal alloys. Gaseous solutions - air and other mixtures of gases.
Dissolution process. Dissolution is a complex physical and chemical process. During the physical process, the structure of the dissolved substance is destroyed and its particles are distributed between the solvent molecules. A chemical process is the interaction of solvent molecules with solute particles. As a result of this interaction, solvates. If the solvent is water, then the resulting solvates are called hydrates. The process of formation of solvates is called solvation, the process of formation of hydrates is called hydration. When aqueous solutions are evaporated, crystalline hydrates are formed - these are crystalline substances, which include a certain number of water molecules (water of crystallization). Examples of crystalline hydrates: CuSO 4 . 5H 2 O - copper (II) sulfate pentahydrate; FeSO4 . 7H 2 O - iron sulfate heptahydrate (II).
The physical process of dissolution proceeds with takeover energy, chemical highlighting. If as a result of hydration (solvation) more energy is released than it is absorbed during the destruction of the structure of a substance, then dissolution - exothermic process. Energy is released during the dissolution of NaOH, H 2 SO 4 , Na 2 CO 3 , ZnSO 4 and other substances. If more energy is needed to destroy the structure of a substance than it is released during hydration, then dissolution - endothermic process. Energy absorption occurs when NaNO 3 , KCl, NH 4 NO 3 , K 2 SO 4 , NH 4 Cl and some other substances are dissolved in water.
The amount of energy released or absorbed during dissolution is called thermal effect of dissolution.
Solubility substance is its ability to be distributed in another substance in the form of atoms, ions or molecules with the formation of a thermodynamically stable system of variable composition. The quantitative characteristic of solubility is solubility factor, which shows what is the maximum mass of a substance that can be dissolved in 1000 or 100 g of water at a given temperature. The solubility of a substance depends on the nature of the solvent and substance, on temperature and pressure (for gases). The solubility of solids generally increases with increasing temperature. The solubility of gases decreases with increasing temperature, but increases with increasing pressure.
According to their solubility in water, substances are divided into three groups:
1. Highly soluble (p.). The solubility of substances is more than 10 g in 1000 g of water. For example, 2000 g of sugar dissolves in 1000 g of water, or 1 liter of water.
2. Slightly soluble (m.). The solubility of substances is from 0.01 g to 10 g in 1000 g of water. For example, 2 g of gypsum (CaSO 4 . 2 H 2 O) dissolves in 1000 g of water.
3. Practically insoluble (n.). The solubility of substances is less than 0.01 g in 1000 g of water. For example, in 1000 g of water, 1.5 . 10 -3 g AgCl.
When substances are dissolved, saturated, unsaturated and supersaturated solutions can be formed.
saturated solution is the solution that contains the maximum amount of solute under given conditions. When a substance is added to such a solution, the substance no longer dissolves.
unsaturated solution A solution that contains less solute than a saturated solution under given conditions. When a substance is added to such a solution, the substance still dissolves.
Sometimes it is possible to obtain a solution in which the solute contains more than in a saturated solution at a given temperature. Such a solution is called supersaturated. This solution is obtained by carefully cooling the saturated solution to room temperature. Supersaturated solutions are very unstable. Crystallization of a substance in such a solution can be caused by rubbing the walls of the vessel in which the solution is located with a glass rod. This method is used when performing some qualitative reactions.
The solubility of a substance can also be expressed by the molar concentration of its saturated solution (section 2.2).
Solubility constant. Let us consider the processes that occur during the interaction of a poorly soluble but strong electrolyte of barium sulfate BaSO 4 with water. Under the action of water dipoles, Ba 2+ and SO 4 2 - ions from the crystal lattice of BaSO 4 will pass into the liquid phase. Simultaneously with this process, under the influence of the electrostatic field of the crystal lattice, part of the Ba 2+ and SO 4 2 - ions will again precipitate (Fig. 3). At a given temperature, an equilibrium will finally be established in a heterogeneous system: the rate of the dissolution process (V 1) will be equal to the rate of the precipitation process (V 2), i.e.
BaSO 4 ⇄ Ba 2+ + SO 4 2 -
solid solution
Rice. 3. Saturated barium sulfate solution
A solution in equilibrium with the BaSO 4 solid phase is called rich relative to barium sulfate.
A saturated solution is an equilibrium heterogeneous system, which is characterized by a chemical equilibrium constant:
, (1)
where a (Ba 2+) is the activity of barium ions; a(SO 4 2-) - activity of sulfate ions;
a (BaSO 4) is the activity of barium sulfate molecules.
The denominator of this fraction - the activity of crystalline BaSO 4 - is a constant value equal to one. The product of two constants gives a new constant called thermodynamic solubility constant and denote K s °:
K s ° \u003d a (Ba 2+) . a(SO 4 2-). (2)
This value was previously called the solubility product and was designated PR.
Thus, in a saturated solution of a poorly soluble strong electrolyte, the product of the equilibrium activities of its ions is a constant value at a given temperature.
If we accept that in a saturated solution of a sparingly soluble electrolyte, the activity coefficient f~1, then the activity of ions in this case can be replaced by their concentrations, since a( X) = f (X) . WITH( X). The thermodynamic solubility constant K s ° will turn into the concentration solubility constant K s:
K s \u003d C (Ba 2+) . C(SO 4 2-), (3)
where C(Ba 2+) and C(SO 4 2 -) are the equilibrium concentrations of Ba 2+ and SO 4 2 - ions (mol / l) in a saturated solution of barium sulfate.
To simplify calculations, the concentration solubility constant K s is usually used, taking f(X) = 1 (Appendix 2).
If a poorly soluble strong electrolyte forms several ions during dissociation, then the expression K s (or K s °) includes the corresponding powers equal to the stoichiometric coefficients:
PbCl 2 ⇄ Pb 2+ + 2 Cl-; K s \u003d C (Pb 2+) . C 2 (Cl -);
Ag3PO4 ⇄ 3 Ag + + PO 4 3 - ; K s \u003d C 3 (Ag +) . C (PO 4 3 -).
In general, the expression for the concentration solubility constant for the electrolyte A m B n ⇄ m A n+ + n B m - has the form
K s \u003d C m (A n+) . C n (B m -),
where C are the concentrations of A n+ and B m ions in a saturated electrolyte solution in mol/l.
The value of K s is usually used only for electrolytes, the solubility of which in water does not exceed 0.01 mol/l.
Precipitation conditions
Suppose c is the actual concentration of ions of a sparingly soluble electrolyte in solution.
If C m (A n +) . With n (B m -) > K s , then a precipitate will form, because the solution becomes supersaturated.
If C m (A n +) . C n (B m -)< K s , то раствор является ненасыщенным и осадок не образуется.
Solution properties. Below we consider the properties of nonelectrolyte solutions. In the case of electrolytes, a correction isotonic coefficient is introduced into the above formulas.
If a non-volatile substance is dissolved in a liquid, then the saturation vapor pressure over the solution is less than the saturation vapor pressure over the pure solvent. Simultaneously with the decrease in vapor pressure over the solution, a change in its boiling and freezing point is observed; the boiling points of solutions increase, and the freezing points decrease in comparison with the temperatures characterizing pure solvents.
The relative decrease in the freezing point or the relative increase in the boiling point of a solution is proportional to its concentration:
∆t = K С m ,
where K is a constant (cryoscopic or ebullioscopic);
C m is the molar concentration of the solution, mol/1000 g of the solvent.
Since C m \u003d m / M, where m is the mass of the substance (g) in 1000 g of solvent,
M - molar mass, the above equation can be represented:
; .
Thus, knowing the value of K for each solvent, setting m and experimentally determining ∆t in the device, one finds M of the solute.
The molar mass of a solute can be determined by measuring the osmotic pressure of a solution (π) and calculated using the van't Hoff equation:
; .
Laboratory work
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Author - Sevostyanova Lyudmila Nikolaevna, teacher of chemistry of the highest qualification category of the municipal autonomous general educational institution of secondary school No. 3 r.p. Ilyinogorsk, Volodarsky municipal district of the Nizhny Novgorod region
Designation of the subject content of the project. Students gain an understanding of dissolution as a physical and chemical process, the concept of hydrates and crystalline hydrates, solubility, solubility curves, as a model of the dependence of dissolution on temperature, saturated, supersaturated and unsaturated solutions. Draw conclusions about the importance of solutions for nature and agriculture.
The methodological development was compiled on the basis of the program of basic general education in chemistry, the educational and methodological complex of O.S. Gabrielyan “Chemistry. 8-11 grades (Working programs. Chemistry 8-11 grades: teaching aid / compiled by G.M. Paldyaev. - 2nd ed., stereotype. M .: Bustard, 2013). This concentric course complies with the Federal State Educational Standard for Basic General Education, is approved by the Russian Academy of Education and the Russian Academy of Sciences, has a "Recommended" stamp and is included in the Federal List of Textbooks.
According to the current Basic Curriculum, the work program for the 8th grade provides for teaching chemistry in the amount of 2 hours per week.
Chapter. Dissolution. Solutions. Properties of electrolytes.
Subject. Solubility. Solubility of substances in water.
Justification of the expediency of this subject content for the organization of project / research activities of students. Through the organization of research activities, to form an idea of dissolution as a physical and chemical process. Based on the knowledge and skills gained during active search and independent problem solving, students learn to establish interdisciplinary and cause-and-effect relationships.
Also, this project, aimed at forming an idea of the physicochemical process of dissolution, studying the solubility of various substances under various conditions, ensures the development of a sustainable interest in chemistry.
Project name: Solutions. Solubility of substances in water.
Description of the problem situation, definition of the problem and purpose of the project module. The teacher organizes the actions of students to identify and formulate the problem, inviting students to conduct a mini-study "Preparation of aqueous solutions of potassium permanganate and sulfuric acid." During the experiments, students note that in the process of dissolving substances, both signs of a physical and signs of a chemical phenomenon are observed.
The students and the teacher formulate a contradiction.
Contradiction: In the process of dissolution, on the one hand, signs of physical phenomena can be observed, on the other, chemical phenomena.
Problem: Is the process of "dissolution" a chemical or physical process? Is it possible to influence this process?
Description of the project product/result with evaluation criteria.
Purpose of the project module: prove the essence of the dissolution process and explain the dependence of solubility on various factors through the creation of a mental map "Solubility of substances in water".
Project product: mental map "Solubility of substances in water".
The mental map is a systematized and visualized material. The theme of the project "Solubility of Substances" is written in the center. Based on the conducted mini-research, students are invited to formulate conclusions and creatively arrange them in several blocks:
Each individual project product of the pair is evaluated against the following criteria.
- Aesthetics of design
- Structural design
- Consistency of design
- visibility
- 1 point - partially presented
Rating "5" - 15-14 points
Rating "4" - 13-11 points
Grade "3" - 10-7 points
Score "2" - less than 7 points
Determination of the total amount of lesson hours required for the implementation of the project, and its distribution by stages of the project activities of students, indicating the actions of the teacher and students.
The project module includes 3 lessons (3 hours of the project module are implemented at the expense of 1 hour, which is allotted for studying the topic "Solutions. Solubility of substances" and 2 hours due to reserve time):
PD phases |
Stages of PD |
lesson planning |
Design |
Update |
1 lesson Homework |
Problematization |
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goal setting |
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Planning |
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Conceptualization Modeling |
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Implementation |
Criteria base development |
2 lesson Homework |
Implementation of the project product |
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Presentation of the project product Grade Reflection |
Performance |
3 lesson Homework |
Project Protection |
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Reflection |
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Diagnostics of the level of formation of project actions |
A phased description of the project module, the actions of students, the actions of the teacher.
Stages of project activity |
Teacher activity |
Student activities |
Facilities |
Result |
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Lesson 1 (preparatory and design stages): actualization - problematization - goal setting - action planning - conceptualization. |
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Updating the existing system: subject knowledge and methods of activity, meta-subject methods of activity, values and meanings associated with the content of the module and the process of cognition itself. |
Organizes the repetition of safety rules and behavior in the chemistry room. Organizes the frontal execution of tasks aimed at mastering the topic "Physical and chemical phenomena" Asks students a question: “How to distinguish chemical phenomena from physical ones?”, “What are the signs of chemical reactions?” |
They answer questions. Viewing in "silent" mode flash - movie "Signs of chemical reactions". Indicate signs of chemical reactions, comment on their answer. They argue and conclude that chemical phenomena are characterized by the formation of new substances, with new features. Signs of chemical reactions can be: the appearance of an odor (gas evolution), the formation of a precipitate, a change in color. |
Multimedia complex and interactive whiteboard. Material of the Unified Collection of the DER |
The border of "knowledge-ignorance" is revealed |
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Problematization– identifying the problem of the project and the causes leading to the appearance of the problem. |
Organizes students' actions to identify and formulate contradictions and problems. Conducting a mini-study: "Preparation of aqueous solutions of potassium permanganate and sulfuric acid" |
Students, observing the safety rules, perform mini-study No. 1: describe their observations, fill out the table. Dissolution
Problem: What phenomena does the process of dissolution refer to, physical or chemical, how can the process of dissolution of substances be described? |
Algorithm for performing a mini-study No. 1 Application No. 1 Equipment and reagents: : KMnO 4 , H 2 SO 4 (conc.), anhydrous CuSO 4 , water, test tubes, rack. |
The problem is formulated |
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goal setting– definition of the purpose and objectives of the project. |
Based on the formulated problem, creates conditions for formulating the goal and determining the future project product |
Formulate the goal of the project with the help of a teacher: describe the model of the dissolution process, determine the factors influencing the dissolution process, classify solutions, indicate the meaning and use of solutions. With the help of the teacher, the blocks of the mental map are determined: 1 block: "Model of the dissolution process" Block 2: "Dependence of the dissolution process on various factors" Block 3: "Classification of solutions" Block 4: "The meaning and use of solutions" |
The goal of the overall project product is formulated. |
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Action planning |
Creates conditions for the formation of project teams and the distribution of responsibilities within the groups for the implementation of project tasks
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The class is divided into 5 groups of 4-5 people. Each group chooses a leader. Together with the teacher, they pronounce a joint action plan.
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Formed groups of students to complete the project. A plan for further work has been developed |
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Organizes student activities to work in groups. Assists in the distribution of responsibilities within the group Offers work in groups on single tasks: read the text of the textbook pp. 186-188, draw up a diagram-model of the dissolution process. Guides groups to complete Practical Mini-Study #2 Observing the Influence of the Nature of the Solute on the Dissolution Process Guides groups to complete practical mini-study No. 3 "Observation of the influence of the nature of the solvent on the process of dissolving substances" Directs groups to carry out a practical mini-study No. 4 "Observation of the effect of temperature on the solubility of substances.". |
Make up a scheme-model "Dissolution as a physical and chemical process." Each student in the group reads the text independently. 1 student: considers the history of the study of this issue. 2 student: identifies supporters of the physical theory of solutions 3 student: identifies supporters of the chemical theory of solutions 4 student: describe modern ideas, draw up a model diagram SOLUTION = H2O + R.V. + HYDRATES(products of H2O interaction solutes). 5 the student plans and draws up block 1 of the mental map. Students, observing the safety rules, perform mini-study No. 2 "Observation of the influence of the nature of the solute on the dissolution process" according to the proposed algorithm, formulate a conclusion. Formulate conclusions: The nature of the solute affects the dissolution process. The solubility of a substance depends on the nature of the substance itself. Students, observing the safety rules, perform a mini-study No. 3 "Observation of the influence of the nature of the solvent on the process of dissolution of substances" according to the proposed algorithm, formulate a conclusion. Formulate conclusions: The nature of the solvent affects the solvent process. The solubility of a substance depends on the nature of the substance itself. Students, observing the safety rules, perform a mini-study No. 4 “Observation of the effect of temperature on the solubility of substances.” According to the proposed algorithm, they formulate a conclusion. Formulate conclusions: With increasing temperature, the solubility of a substance increases. It is possible to build a model of solubility depending on temperature. |
Design assignments "Brainstorm" Mini-Study Algorithm #2 Annex 2 Equipment and reagents: numbered test tubes with substances: No. 1 Calcium chloride No. 2 Calcium hydroxide No. 3 Calcium carbonate, water. Mini-Study Algorithm #3 Annex 3 Equipment and reagents: Two numbered test tubes No. 1 and No. 2 with several iodine crystals, alcohol, water. Mini-Study Algorithm #4 Appendix 4 |
Intermediate products have been created: a scheme is a model of the dissolution process. Factors affecting the solubility of substances are formulated:
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Conceptualization and modeling - object image creation design. |
Organizes the actions of students to create an image of the project product. Advises students on the creation of a project product. |
Students in groups discuss what the final module will be, argue their point of view, listen to the students of their group, and participate in the discussion of the layout. . |
Brainstorm |
An image (model) of the project product was created - the mental map "Solubility of substances" |
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Organizes the work on the distribution of blocks within the group, organizes the work on filling out the time sheet for work on the project |
They choose a block to fill, negotiate with each other, offer mutual assistance in the distribution and design of blocks. Evaluate their own work and the work of classmates |
Project worksheet |
All blocks within each group are distributed, the work for the lesson is evaluated. |
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D/z: study paragraph 34, complete the tasks in the workbook. Select illustrations for blocks to the mental map, illustrating the classification and application of solutions. |
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Lesson 2 (implementation stage): solving specific practical problems. Creation of a project product. |
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Criteria base development |
Organizes work on the creation of project criteria |
They offer options for evaluating the project product:
For each criterion from 0 to 3 points:
Rating "5" - 15-14 points Rating "4" - 13-11 points Grade "3" - 10-7 points Score "2" - less than 7 points |
Reception "Opinion Tree" |
Project evaluation criteria developed |
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Solving specific practical problems and creating educational products(creation of a project product) |
Creates conditions for the implementation of the project product. The implementation of the project task is organized, the requirements for compiling a mental map, the requirements for structuring the information found are considered Each group receives a project task and an algorithm for its implementation, Provides consulting assistance in creating a project product. |
Students, in accordance with the distributed responsibilities, determine the image of a specific practical task. This will be a mental map on which information will be structured on the topic “Solubility of substances. Solutions. The topic will be in the center. There are 4 blocks around. Information should be presented in the form of diagrams, drawings, associations. Students distribute responsibilities in a group: 1 student: responsible for unit No. 1, group commander 2 student: responsible for block No. 2, tracking time; 3 student: responsible for block number 3, 4 student: responsible for block number 4 5 student: general design of the work, responsible for evaluating the work performed. Performing tasks jointly, but under the control of the responsible person:
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Paper, markers, scissors, printer |
Design assignments completed. A design semi-finished product has been created. |
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D / z: repeat paragraph 34. Finalize the created project semi-finished product, prepare a presentation from the group. |
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Lesson 3 “Presentation of the resulting project product. Evaluation of the quality of the product and reflection of actions in the project of its creators. |
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Presentation of the received project product. |
Creates conditions for the presentation of the project product |
They present the created project products - a mental map assembled from 4 blocks. |
Demonstration of the map “Dissolution-bridge. Solutes." |
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Evaluation of the quality of the project product and reflection of the actions in the project of its creators. |
Organizes the generalization of knowledge and performed actions. It offers to correlate the tasks and results of creating the project, to evaluate the correctness of the choice of the project method. Summarizes the knowledge gained, the actions performed. Uses criteria to evaluate results. Evaluates the acquired knowledge and mastered actions in accordance with the criteria. Controls knowledge on the topic “Dissolution. Solubility of substances. |
Groups come out to defend their product. Evaluate their work in the group for the implementation of project activities, the work of classmates; and evaluate projects. Dispute or agree with the assessment of their work. Analyze the deficiencies. Make suggestions to the algorithm for performing tasks of the same type. Evaluate the project activity in accordance with the criteria of the evaluation sheet. |
Evaluation sheet of project activities. Application No. 5 Design Product Evaluation Sheet Application No. 6 The task "Insert the missing word" by options. |
Ratings posted. Errors indicated. Reflection done. Knowledge control. |
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D/z: complete the tasks of the textbook p.192. Prepare messages about solutions used in medicine - 1st row, in agriculture - 2nd row, in everyday life - 3rd row. |
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Description of intermediate project products and description of lesson homework assignments used (didactic support of the project module).
At the first lesson, the teacher checks the level of assimilation of the previously studied topic, offers to verbally complete the task to update knowledge - Viewing in the "silent" mode of the flash video "Signs of chemical reactions", Material of the Unified Collection of the CER
Based on the results of the work in the first lesson, students receive intermediate products: mini-study reports No. 1 “Observation of the processes of dissolution of potassium permanganate, concentrated sulfuric acid and anhydrous copper sulfate”, No. 2 Observation of the influence of the nature of the solute on the dissolution process”, No. 3 “ Observation of the influence of the nature of the solvent on the dissolution process, No. 4 “Observation of the influence of temperature on the dissolution process”
Students receive the following task at home: study paragraph 34, complete the task in the workbook, part I, topic 34, using an Internet source, select illustrations on the topics “The meaning and use of solutions”, “Classification of solutions”.
In the second lesson, students develop a project product in accordance with project assignments. At the end of the lesson, each group draws up a mental map. After the second lesson, students receive homework: finalize the project semi-finished product and prepare a mini-speech on it, including preparation for the project and its implementation.
After the third lesson, students receive homework: to prepare a report on the use of solutions in everyday life, agriculture or medicine.
Solubility (R, χ or k s) – this is a characteristic of a saturated solution, which shows what mass of a solute can be dissolved in 100 g of solvent as much as possible. The solubility dimension is g/ 100 g water. Since we are determining the mass of salt that falls on 100 g of water, we add a factor of 100 to the solubility formula:
here m r.v. is the mass of the dissolved substance, g
m r-la is the mass of the solvent, g
Sometimes the designation is used solubility factor k S .
Solubility tasks, as a rule, cause difficulties, since this physical quantity is not very familiar to schoolchildren.
The solubility of substances in various solvents varies widely.
The table shows the solubility of some substances in water at 20 o C:
Substance | Substance | Solubility, g per 100 g H 2 O |
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NH4NO3 | H3BO3 | ||
NaCl | CaCO3 | 0,0006 |
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NaHCO3 | 0,0000002 |
What does the solubility of substances depend on? From a number of factors: from the nature of the solute and solvent, from temperature and pressure. The reference tables suggest substances are divided into highly soluble, slightly soluble and insoluble. This division is very conditional, since there are no absolutely insoluble substances. Even silver and gold are soluble in water, but their solubility is so low as to be negligible.
Dependence of solubility on the nature of the solute and solvent*
Solubility of solids in liquids depends on the structure of the solid (on the type of crystal lattice of the solid). for example, substances with metallic crystal lattices (iron, copper, etc.) are very slightly soluble in water. Substances with an ionic crystal lattice, as a rule, are highly soluble in water.
There is a wonderful rule: like dissolves in like". Substances with an ionic or polar type of bond dissolve well in polar solvents.for example salts are highly soluble in water. At the same time, non-polar substances, as a rule, dissolve well in non-polar solvents.
Most alkali metal and ammonium salts are highly soluble in water. Almost all nitrates, nitrites and many halides (except silver, mercury, lead and thallium halides) and sulfates (except alkaline earth metal, silver and lead sulfates) are highly soluble. Transition metals are characterized by a low solubility of their sulfides, phosphates, carbonates, and some other salts.
The solubility of gases in liquids also depends on their nature. For example, in 100 volumes of water at 20 o C dissolves 2 volumes of hydrogen, 3 volumes of oxygen. Under the same conditions, 700 volumes of ammonia dissolve in 1 volume of H 2 O.
Effect of temperature on the solubility of gases, solids and liquids*
The dissolution of gases in water due to the hydration of the dissolved gas molecules is accompanied by the release of heat. Therefore, as the temperature rises, the solubility of gases decreases.
Temperature affects the solubility of solids in water in various ways. In most cases solubility of solids increases with temperature. for example, the solubility of sodium nitrate NaNO 3 and potassium nitrate KNO 3 increases when heated (the dissolution process proceeds with the absorption of heat). The solubility of NaCl increases slightly with increasing temperature, which is due to the almost zero thermal effect of the dissolution of table salt.
Effect of pressure on the solubility of gases, solids and liquids*
The solubility of solid and liquid substances in liquids is practically not affected by pressure, since the change in volume during dissolution is small. When gaseous substances are dissolved in a liquid, the volume of the system decreases, therefore, an increase in pressure leads to an increase in the solubility of gases. In general, the dependence of the solubility of gases on pressure obeys W. Henry's law(England, 1803): the solubility of a gas at constant temperature is directly proportional to its pressure over the liquid.
Henry's law is valid only at low pressures for gases whose solubility is relatively low and provided there is no chemical interaction between the molecules of the dissolved gas and the solvent.
Influence of foreign substances on solubility*
In the presence of other substances (salts, acids and alkalis) in water, the solubility of gases decreases. The solubility of gaseous chlorine in a saturated aqueous solution of table salt is 10 times less. than pure water.
The effect of decreasing solubility in the presence of salts is called salting out. The decrease in solubility is due to the hydration of salts, which causes a decrease in the number of free water molecules. Water molecules associated with electrolyte ions are no longer a solvent for other substances.
Examples of problems for solubility
Task 1. The mass fraction of a substance in a saturated solution is 24% at a certain temperature. Determine the solubility coefficient of this substance at a given temperature.
Decision:
To determine the solubility of a substance, we take the mass of the solution equal to 100 g. Then the mass of salt is equal to:
m r.v. = m r-ra ⋅ω r.v. = 100⋅0.24 = 24 g
The mass of water is:
m water \u003d m solution - m r.v. = 100 - 24 = 76 g
Determine the solubility:
χ = m r.v. /m p-la ⋅100 = 24/76⋅100 = 31.6 g of substance per 100 g of water.
Answer: χ = 31.6 g
A few more similar issues:
2. The mass fraction of salt in a saturated solution at a certain temperature is 28.5%. Determine the solubility coefficient of the substance at this temperature.
3. Determine the solubility coefficient of potassium nitrate at a certain temperature, if the mass fraction of salt at this temperature is 0.48.
4. What mass of water and salt will be required to prepare 500 g of a solution of potassium nitrate saturated at a certain temperature, if its solubility coefficient at this temperature is 63.9 g of salt per 100 g of water?
Answer: 194.95 g
5. The solubility coefficient of sodium chloride at a certain temperature is 36g of salt in 100g of water. Determine the molar concentration of a saturated solution of this salt if the density of the solution is 1.2 g/ml.
Answer: 5.49M
6. What mass of salt and 5% of its solution will be required to prepare 450 g of a solution of potassium sulfate saturated at a certain temperature, if its solubility coefficient at this temperature is 439 g / 1000 g of water?
7. What mass of barium nitrate will be released from a solution saturated at 100ºС and cooled to 0ºС if there was 150 ml of water in the solution taken? The solubility coefficient of barium nitrate at temperatures of 0ºС and 100ºС is 50 g and 342 g in 100 g of water, respectively.
8. The solubility coefficient of potassium chloride at 90ºС is 500g/l of water. How many grams of this substance can be dissolved in 500 g of water at 90ºC and what is its mass fraction in a saturated solution at this temperature?
9. 300 g of ammonium chloride are dissolved in 500 g of water when heated. What mass of ammonium chloride will be released from the solution when it is cooled to 50ºС, if the solubility coefficient of the salt at this temperature is 50 g/l of water?
* Materials of the portal onx.distant.ru
Today we will talk about the substance - water!
Have any of you seen water?
Did the question seem ridiculous to you? But it refers to completely pure water, in which there are no impurities. To be honest and accurate in the answer, you will have to admit that neither I nor you have seen such water yet. That is why on a glass of water after the inscription "H 2 O" there is a question mark. So, there is not pure water in the glass, but what then?
Gases dissolved in this water: N 2, O 2, CO 2, Ar, salts from the soil, iron cations from water pipes. In addition, the smallest particles of dust are suspended in it. That's what we call h and s t o y water! Many scientists are working on solving the difficult problem of obtaining absolutely pure water. But so far it has not been possible to obtain such ultrapure water. However, you may object that there is distilled water. By the way, what is she?
In fact, we get such water when we sterilize the jars before canning. Turn the jar upside down and place it over boiling water. Droplets appear on the bottom of the jar, this is distilled water. But as soon as we turn the jar over, gases from the air enter it, and again there is a solution in the jar. Therefore, competent housewives try to fill the jars with the necessary contents immediately after sterilization. They say that the products in this case will be stored longer. Perhaps they are right. Feel free to experiment! Precisely because water is capable of dissolving various substances in itself, scientists still cannot obtain ideally pure water in large volumes. And it would be so useful, for example, in medicine for the preparation of medicines.
By the way, being in a glass, water "dissolves" the glass. Therefore, the thicker the glass, the longer the glasses will last. What is sea water?
This is a solution that contains many substances. For example, table salt. How can salt be isolated from sea water?
Evaporation. By the way, this is exactly what our ancestors did. There were salt pans in Onega, where salt was evaporated from sea water. Salt was sold to Novgorod merchants, they bought expensive jewelry and chic fabrics for their brides and wives. Even the Moscow fashionistas did not have such outfits as the Pomoroks. And all only thanks to the knowledge of the properties of solutions! So, today we are talking about solutions and solubility. Write down the definition of the solution in your notebook.
A solution is a homogeneous system consisting of solvent and solute molecules, between which physical and chemical interactions occur.
Consider schemes 1–2 and analyze what solutions are.
Which solution would you prefer when making soup? Why?
Determine where is the dilute solution, where is the concentrated solution of copper sulphate?
If a certain volume of a solution contains little solute, then such a solution is called diluted, if a lot - concentrated
.
Determine which solution is where?
Do not confuse the concepts of "saturated" and "concentrated" solution, "unsaturated" and "dilute" solution.
Some substances dissolve well in water, others little, and still others do not dissolve at all. Watch the video "SOLUBILITY OF SOLIDS IN WATER"
Complete the task in the notebook: Distribute the proposed substances -CO 2, H 2, O 2 , H 2 SO 4 , Vinegar, NaCl, Chalk, Rust, Vegetable oil, Alcoholinto the empty columns of table 1, using your life experience.
Table 1
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Dissolved |
Substance examples |
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Soluble |
Slightly soluble |
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Gas |
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Liquid |
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Solid |
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Can you tell me about the solubility FeSO4?
How to be?
In order to determine the solubility of substances in water, we will use the table of the solubility of salts, acids and bases in water. It is in the attachments to the lesson.
In the top row of the table are cations, in the left column are anions; we are looking for an intersection point, we look at the letter - this is solubility.
Let's determine the solubility of salts: AgNO 3 , AgCl, CaSO 4 .
Solubility increases with increasing temperature (there are exceptions). You know perfectly well that it is more convenient and faster to dissolve sugar in hot water than in cold water. See "Thermal Phenomena in Dissolution"
Try it yourself, using the table, to determine the solubility of substances.
Exercise. Determine the solubility of the following substances: AgNO 3 , Fe (OH) 2 , Ag 2 SO 3 , Ca (OH) 2 , CaCO 3 , MgCO 3 , KOH.
DEFINITIONS on the topic "Solutions"
Solution- a homogeneous system consisting of solvent and solute molecules, between which physical and chemical interactions occur.
saturated solution A solution in which a given substance no longer dissolves at a given temperature.
unsaturated solution A solution in which a substance can still dissolve at a given temperature.
suspensioncalled a suspension in which small particles of solid matter are evenly distributed among water molecules.
emulsioncalled a suspension in which small droplets of a liquid are distributed among the molecules of another liquid.
dilute solutions - solutions with a small content of dissolved substance.
concentrated solutions - solutions with a high content of solute.
ADDITIONALLY:
According to the ratio of the predominance of the number of particles passing into the solution or removed from the solution, solutions are distinguished saturated, unsaturated and supersaturated. According to the relative amounts of solute and solvent, solutions are divided into diluted and concentrated.
A solution in which a given substance at a given temperature no longer dissolves, i.e. a solution in equilibrium with a solute is called rich, and a solution in which an additional amount of a given substance can still be dissolved, - unsaturated.
A saturated solution contains the maximum possible (for given conditions) amount of solute. Therefore, a saturated solution is one that is in equilibrium with an excess of solute. The concentration of a saturated solution (solubility) for a given substance under strictly defined conditions (temperature, solvent) is a constant value.
A solution containing more solute than it should be under the given conditions in a saturated solution is called supersaturated. Supersaturated solutions are unstable, non-equilibrium systems in which a spontaneous transition to an equilibrium state is observed. In this case, an excess of the solute is released, and the solution becomes saturated.
Saturated and unsaturated solutions should not be confused with dilute and concentrated solutions. dilute solutions- solutions with a small content of a dissolved substance; concentrated solutions- solutions with a high content of solute. It must be emphasized that the concepts of dilute and concentrated solutions are relative, expressing only the ratio of the amounts of a solute and a solvent in a solution.
