"Representation of Solution Concentration" Solution PPT Courseware 4

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"Representation of Solution Concentration" Solution PPT Courseware 4

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1. The concentration of the solution

1. The concentration of a colored solution can be roughly expressed by the solution ____________, but it cannot be expressed for a colorless solution.

2. To quantitatively express the concentration of a solution, the solute mass fraction method is often used.

(1) Definition: The mass fraction of solute refers to the ratio of _________ to __________.

(2) Calculation formula: Mass fraction of solute = mass of solute/mass of solution × 100% = mass of solute/mass of solute + mass of solvent × 100%.

3. For liquid solutes, volume fraction is often used to quantitatively express the concentration of a solution.

2. Simple calculation of solute mass fraction

Mass of solute = mass of solution × mass fraction of solute

Mass of solution = Mass of solute/Mass fraction of solute

3. The relationship between saturated solution, unsaturated solution, concentrated solution and dilute solution

1. Saturated solutions and unsaturated solutions are defined based on whether the solute can be ___________ in the solution, while concentrated solutions and dilute solutions are defined based on the amount of solute contained in a certain amount of solution. They are classifications of solutions from different perspectives.

2. For different substances, when the temperature and the amount of solvent are constant, when different substances reach a saturated state, the amount of dissolved solutes will be more or less, and the solutions formed will be either concentrated or dilute, so the saturated solution ________(fill in "certain" or "not necessarily", the same below) is a concentrated solution, and an unsaturated solution __________ is a dilute solution.

3. For the same solute, at the same temperature and in the same mass of solvent, a saturated solution can dissolve more solute than an unsaturated solution, so the ________ solution at the same temperature is more concentrated than the ________ solution.

Interactive exploration

Research point 1: The concentration of the solution

[Scenario Display]Observe the colors of copper sulfate solutions with different concentrations (as shown in the picture):

[Question Investigation]Is the color depth of the colored solution related to the concentration of the solution? How do we quantitatively express the concentration of a solution?

[Inductive improvement]The depth of color of a colored solution can roughly reflect the concentration of the solution. The greater the concentration of the solution, the darker the color of the colored solution; the smaller the concentration, the lighter the color of the colored solution. However, to accurately solve the problem of concentration of colored and colorless solutions, we must use the concentration of the solution to express it quantitatively. The concentration of a solution is the mass fraction of the solute, that is, the amount of solute contained in a certain amount of solution (the ratio of the solute mass to the solution mass).

[Application Example]

Example 1: Add 12.5 g NaOH solid to 100 g 10% NaOH solution. After it is completely dissolved, the mass fraction of the solute in the resulting solution is ()

A． 12.5%B． 20%

C. 22.5% D． 25%

[Method Instructions] When calculating the mass fraction of a solute, it is necessary to clarify: what the solute is and what its mass is; what components the solution contains and what their masses are. Be careful not to omit “×100%” and the mass unit in the calculation formula.

Exploration point 2: Calculation of solution dilution problems

[Scenario Display]Add a certain amount of 98% concentrated sulfuric acid to a certain amount of water, or add a certain solute mass fraction of dilute sulfuric acid to obtain another dilute sulfuric acid with a certain solute mass fraction.

[Question Research]To dilute 50 g of 98% concentrated sulfuric acid into 49% dilute sulfuric acid, what mass of water needs to be added? If 24.5% dilute sulfuric acid is used, what is the mass of water required?

[Inductive improvement]The solution mass changes before and after the solution is diluted, the concentration changes, but the solute mass does not change. This is often used to find the equivalence relationship. The mass of the concentrated solution The mass of the solute in the solution (calculated by using the constant mass of the solute before and after mixing) = the mass of the concentrated solution × the mass fraction of the solute in the concentrated solution + the mass of the dilute solution × the mass fraction of the solute in the dilute solution = (mass of the concentrated solution + The mass of the dilute solution) × the mass fraction of the solute in the resulting solution.

[Application Example]

Example 2 2013·Nanjing If you want to prepare 245 g of dilute sulfuric acid with a mass fraction of 10%, you need 98% concentrated sulfuric acid (density of 1.84 g/cm3) __________mL (calculation results should be kept to one decimal place). When preparing a dilute solution from a concentrated solution, the calculation is based on the fact that the mass of the solute remains unchanged before and after the solution is diluted.

[Method Instructions] The mass of the solution changes before and after the solution is diluted, the concentration changes, but the mass of the solute does not change. This is often used to find the equivalence relationship. The mass of the concentrated solution × the mass fraction of the solute in the concentrated solution = the mass of the dilute solution × the mass fraction of the solute in the dilute solution.

On-site testing

Knowledge point 1: Simple calculation of the mass fraction of solute

1. To prepare 2000 g of physiological saline with a solute mass fraction of 0.9%, the mass of NaCl needs to be weighed ()

A． 9 g B. 18 g

C. 90 g D. 180g

2. To prepare 50 g of a glucose solution with a mass fraction of 8% solute, _______g of solid glucose is required; if _______g of a glucose solution with a mass fraction of 20% solute is used and water is added, it can also be diluted to 50 g of a solution with a mass fraction of 8% solute. .

Knowledge point 2: Solubility (solubility curve) and solute mass fraction synthesis

3. Figure 7-3-3 shows the solubility curves of two solid substances A and B.

(1) At ________°C, the solubilities of the two substances A and B are equal.

(2) At t2°C, ________g of substance A dissolved in 100 g of water is exactly saturated, and the mass fraction of solute in the saturated solution is ______. To dilute this saturated solution to a solution with a mass fraction of 10%, ________g of water should be added.

(3) When t2℃, the exactly saturated solutions of two substances A and B are cooled to t1℃ respectively. The mass fraction of the solute remains unchanged is ________.

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Update Time: 2024-09-08

This template belongs to Chemistry courseware Cantonese Education Edition Ninth Grade Chemistry Volume 2 industry PPT template

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