"Concentration of Solution" Solution PPT Courseware 2

Description

"Concentration of Solution" Solution PPT Courseware 2

learning target:

1. Master the concept and calculation formula of solute mass fraction.

2. Be able to calculate the solute mass fraction.

(such as calculating the mass fraction of solute; the mass of solute, solvent, etc.)

Self-study guidance: Please read carefully the content above "Example 2" in 42-44 of the textbook and pay attention

(1) Understand the concept and calculation formula of solute mass fraction;

(2) Master the problem-solving ideas and steps of Example 1, and be able to solve similar problems. After 7 minutes, let’s see who’s self-study is better!

How to express the composition of a solution

Correctly understand "concentrated" solutions and "dilute" solutions:

You can judge whether a colored solution is "thick" or "thin" by observing its color. The darker color is "thick" and the lighter color is "thin".

Judging by color is only a rough judgment of the "thickness" and "thinness" of the solution. We need to know the specific "thickness" and "thinness" of the solution. We can use the concentration of the solution.

[Discussion]The mass fraction of solute in a certain sodium chloride solution is 10%. What does it mean?

Indicates that 100 parts by mass of sodium chloride solution contains 10 parts by mass of sodium chloride and 90 parts by mass of water.

Solute mass: Solvent mass = 1:9

Definition: The ratio of the mass of the solute to the mass of the solution. (usually expressed as a percentage)

Mass fraction of solute = mass of solute/mass of solution × 100% = mass of solute/mass of solute + mass of solvent × 100%

Notice:

①The mass of the solute: the part of the solute that forms the solution, regardless of what is not dissolved into the solution.

②The mass of the solution = the mass of the solute + the mass of the solvent. (Must distinguish between solute, solvent and solution).

③The upper and lower mass units should be unified when calculating.

④Don’t forget to X100% to get the final percentage.

⑤The mass fraction of a substance is meaningful only if it does not exceed its maximum solubility range.

1. Find the masses of solute and solvent based on a certain amount of solution

Example 1: In agricultural production, it is often necessary to use a sodium chloride solution with a mass fraction of 16% for seed selection. Now to prepare 150kg of this solution, what is the mass of sodium chloride and water required?

Solution: Mass fraction of solute = mass of solute/mass of solution × 100%

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

=150kg×16% = 24kg

Solvent mass = Solution mass - Solute mass

=150 kg - 24 kg =126 kg

Answer: Preparing 150kg of sodium chloride solution with a mass fraction of 16% requires 24kg of sodium chloride and 126kg of water.

Exercise: 3 (Textbook P45) At a certain temperature, 35g of potassium chloride solution is evaporated to dryness to obtain 7g of potassium chloride. Find the mass fraction of the solute in the solution.

[Solution] Mass fraction of solute = mass of solute/mass of solution × 100%

Mass fraction of solute = 7g/35g×100% =20%

Answer: The mass fraction of solute in this solution is 20%

Exercise: 4 (Textbook P45) To prepare 500mL of sodium hydroxide solution with a mass fraction of 10% (density 1.1g/cm3), what is the mass of sodium hydroxide and water required?

[Solution] Solution mass = Solution volume × Solution density

= 500mL ×1.1g/cm3 = 550g

Solute mass = 550g ×10% = 55g

Solvent mass = 550g — 55g = 495g

Answer: 55g of sodium hydroxide and 495g of water are required.

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Update Time: 2024-07-29

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