"Understanding Solutions" Solution PPT Courseware 2

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"Understanding Solutions" Solution PPT Courseware 2

Knowledge review

Knowledge point 1 Solution

1. Concept: refers to the dispersion of _____________ substance into _________ substance

Here, a homogeneous and stable mixture is formed.

2. Characteristics: Uniformity, Stability

Homogeneity means that the composition and properties of any part of the solution are exactly the same;

Stability means that the solute will not separate from the solvent when the external conditions remain unchanged (temperature, solvent volume, gas pressure, etc.).

[Note] ①A homogeneous and stable liquid is not necessarily a solution.

Such as water, alcohol, etc.

②Solutions are not necessarily colorless. For example, copper sulfate solution is blue, ferric chloride solution is yellow, etc.

3． Composition: composed of _____, _____. The substance that is dissolved is called ____, and the substance that can dissolve other substances is called ____.

Knowledge point 2: The phenomenon of dissolution

When a substance dissolves, it is usually accompanied by absorption and release of heat. This is because when a substance dissolves, the following two processes occur at the same time:

1. Diffusion process: (also called endothermic process) refers to the diffusion of solute molecules or ions into water;

2. Hydration process: (also called exothermic process) refers to the interaction between solute molecules or ions and water molecules to form hydrated molecules or hydrated ions.

The change in solution temperature when a substance dissolves depends on the relative amounts of heat in these two processes. When more heat is absorbed than released, the solution temperature decreases

For example, _________ dissolves in water; when the heat absorption is less than the heat release, the temperature of the solution rises, as if __________ dissolves in water; when the heat absorption equals the heat release, the temperature of the solution remains unchanged, such as ______ dissolves in water.

[Note] ①The mass of the solution is equal to the sum of the solute mass and the solvent mass, but the volume of the solution is not necessarily equal to the sum of the solute volume and the solvent volume. This is because during the process of dispersing the solute into the solvent, the particles that make up the substance are constantly moving, and the distance between the particles changes. ② When a substance is dissolved in water, the boiling point, freezing point, density, etc. of the solution will often change.

Knowledge point 3: Emulsification

When detergent is added to vegetable oil, the vegetable oil is dispersed into countless tiny droplets and cannot aggregate into large oil droplets. This phenomenon is called __________. Soaps, detergents, etc. all have emulsifying properties.

Example analysis

►Type 1: Formation of solution

Propositional perspective: Test students’ mastery of the basic conditions for forming solutions.

The following cooking condiments cannot form a solution when mixed with enough water ()

A. Table salt b. Rice wine C． White sugar D. olive oil

[Analysis] Olive oil is difficult to dissolve in water and cannot form a solution. Several other condiments are soluble in water and can form a solution.

Variant question Solutions are widely used in our daily lives. Which of the following substances belongs to solutions ()

A. Distilled water b. Iodine c. Lime mortar D. vegetable oil

[Method Instructions] Whether a solution can be formed by mixing substances mainly depends on the solubility of the substance. Therefore, we should pay attention to the solubility of some common substances in life in water.

[ Analysis Calcium hydroxide is not a solution.

►Type 2: Dissolution phenomenon

Proposition perspective: Test students’ understanding of the absorption and release of heat when substances dissolve.

Example 2: When an appropriate amount of the following substances are dissolved in water, the temperature of the solution will be significantly lowered: ()

A. Concentrated sulfuric acid B. Ammonium nitrate

C. caustic soda D. sucrose

[ Analysis The temperature remains basically unchanged.

Variant question: Xiaoqi adds a solid object to the beaker shown in the picture

After stirring, it was found that the temperature increased, the paraffin melted, and the plastic pieces fell off. The substance added by the student may be ()

A. Sucrose b. Ammonium nitrate

C. Sodium chloride d. sodium hydroxide

[Method Instructions] When a substance dissolves, it is often accompanied by a change in heat. It is necessary to memorize the absorption and release of heat when some common substances dissolve. For example, solid sodium hydroxide and concentrated sulfuric acid will release heat when dissolved; the temperature of the solution will decrease when ammonium nitrate is dissolved; the temperature of the solution will almost remain unchanged when salt and sucrose are dissolved. .

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"Understanding Solutions" solution PPT courseware:

"Understanding Solutions" Solution PPT Courseware Exploration Experiment 1: What is a solution? ① Add 10mL of water to the test tube, then add a small amount of salt, shake and let stand ② Add 10mL of water to the test tube, add a small amount of sucrose, shake and let stand ③ Add 10mL of water to the test tube Add a little vegetable oil...

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Update Time: 2024-11-22

This template belongs to Chemistry courseware Beijing Curriculum Reform Edition Ninth Grade Chemistry Volume 2 industry PPT template

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