"Concentration of Solution" Solution PPT Courseware 4

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"Concentration of Solution" Solution PPT Courseware 4

gas solubility

【think】

1. When you open the soda lid, the soda will automatically spurt out. What does this mean about the solubility of gas in water?

Pressure: As the pressure decreases, the solubility of gases in water decreases.

2. I often burp after drinking soda. What else does this show about the solubility of gases?

Temperature: As the temperature increases, the solubility of gases in water decreases.

The solubility of gas: refers to the volume of gas when the gas is dissolved in 1 volume of water and reaches saturation when the pressure is 101kPa and a certain temperature.

3. Gas solubility

1. Factors affecting gas solubility:

Gas solubility generally increases as pressure increases and decreases as pressure decreases.

Gas solubility generally decreases as temperature increases and increases as temperature decreases.

think?

(1) In the experiment to explore the conditions for iron to rust, the distilled water in the second test tube must be boiled. What is the reason?

(2) Fish often float in summer, but rarely in winter. What does this mean?

(3) Fish often float before thunderstorms. What does it mean?

learning target:

1. Understand that mass fraction is one of the ways to describe the concentration of a solution

2. Master the calculation formula of quality score

3. Master the calculation methods of dilution and concentration of solutions

Self-study guide:

1. Calculation formula of mass fraction————————

2. What is quality score?

3. What is the law of dilution?

mass fraction of solute

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:

① Mass of solute: The solute is what is dissolved in the solvent, and insoluble solids cannot be counted.

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.

1. To prepare 100g sodium chloride solution with a solute mass fraction of 10%, the following operations are correct ( )

A. Place 10g of sodium chloride solid directly on the tray of the balance and weigh it

B. When measuring 90ml of water, read from above

C. To speed up the dissolution of the solid, stir the solution with a thermometer

D. Pour the prepared solution into a narrow-mouth bottle, cap the bottle tightly, and label it

2. When preparing a certain mass fraction of sodium chloride solution, the following operational errors will cause the solute mass fraction of the prepared solution to decrease ( )

A. When weighing sodium chloride with a pallet balance, place the weight on the left pan but do not use the balance.

B. When measuring distilled water with a graduated cylinder, look up at the lowest point of the concave liquid surface.

C. When pouring the water from the measuring cylinder into the beaker, water spilled out

D. When transferring the prepared sodium chloride solution to a narrow-mouth bottle, part of the solution was accidentally spilled

Exercise: 1 (Textbook P45) At 20°C, add 40g of potassium nitrate solid to 100g of water. After thorough stirring, there are still 8.4g of potassium nitrate solid that is not dissolved. Please fill in the following blanks:

① The resulting solution is a _______ solution of potassium nitrate at 20°C; (fill in “saturated” or “unsaturated”)

② The solubility of potassium nitrate at 20℃ is _______;

③ The mass fraction of potassium nitrate in the resulting solution is _______.

Exercise: 2 (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: 2024-07-30

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