"Quantitative Expression of Solution Composition" Solution PPT Courseware 3

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"Quantitative Expression of Solution Composition" Solution PPT Courseware 3

Knowledge review

Knowledge point 1: Calculation of solute mass fraction

The solute mass fraction is the ratio of _______ mass to _______ mass.

Related formulas:

①Solute mass fraction = solute mass/solution mass × 100%

②Solution mass =_______ mass +_______ mass

③Solute mass =_______ mass × mass fraction of solute;

Mass of solution = Volume of solution × Density of solution

[Attention]

①The mass fraction of solute is generally expressed as a percentage, not as a fraction.

②The mass fraction is a ratio. Its size is related to both the mass of the solute and the quality of the solution. It does not mean that the mass fraction of the solute must be larger if there is more solute.

③Undissolved substances cannot be included in the solute mass.

Knowledge point 2: Calculation of solution dilution problems

Calculation principle:

During the process of diluting a solution, the mass of ____ does not change.

Calculation formula:

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

Mass of dilute solution × mass fraction of solute in dilute solution.

[Note] ①When two solutions are mixed, the masses can be added or subtracted, but the volumes cannot be added or subtracted.

② The dilution method can be diluting with water or diluting a concentrated solution with a dilute solution. The following equality relationships exist before and after mixing:

Mass of concentrated solution × mass fraction of solute in concentrated solution + mass of dilute solution × mass fraction of solute in dilute solution = mass of mixed solution × mass fraction of solute in mixed solution.

③Keep the units consistent when calculating.

Knowledge point 3: Calculation of solute mass fraction combined with chemical equations

This kind of simple comprehensive calculation is the most common calculation in the high school entrance examination. When calculating, it should be noted that the solute in the solution usually participates in the chemical reaction. Therefore, the corresponding mass of the substance substituted into the chemical equation should be the mass of the solute, not the mass of the solution.

[Tips] If the mass given in the question is the mass of the solution, you must use the solution mass × the mass fraction of the solute to calculate the solute mass and then substitute it into the chemical equation for calculation.

Example analysis

►Type 1: Simple calculation of solute mass fraction

Proposition perspective: Test students’ mastery of simple calculations of solute mass fractions.

Example 1: In agriculture, a sodium chloride solution with a mass fraction of 16% is often used for seed selection. Now we need to prepare 200 kg of this solution. The mass of sodium chloride is ____kg and the mass of water is _____kg.

[Method Instructions] When doing this type of question, you should pay attention to the calculation formula of solute mass fraction and the application of its deformations, and at the same time, you should clearly distinguish the difference between solvent quality and solution quality.

[Analysis] The mass of NaCl needs to be weighed 200 kg×16%=32 kg,

The required mass of water is 200 kg-32 kg=168 kg.

►Type 2: Calculation of dilution issues

Proposition perspective: Test students’ ability to calculate the mass fraction of solutes in the dilution process.

Example 2 Figure 9-1 is part of the label on a certain reagent bottle.

To dilute the concentrated sulfuric acid into 100g of 19.6% dilute sulfuric acid, the mass of the concentrated sulfuric acid is required to be ____g.

[ Method Tips , everyone should pay attention to find out the actual mass of the solution before and after dilution and the corresponding solute mass fraction.

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Update Time: 2024-10-02

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

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