"Concentration of Solution" Solution PPT Courseware 3

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"Concentration of Solution" Solution PPT Courseware 3

The mass fraction of a solute

[Experimental Study 1] Add 0.5g, 1g, and 1.5g of solid copper sulfate to test tubes No. 1, 2, and 3 respectively, and then pour 10 mL of water respectively. After shaking and dissolving, compare the colors of the three copper sulfate solutions.

Experimental phenomenon: The solution in test tube No. 1 has the lightest color; followed by No. 2;

The solution in test tube 3 is the darkest.

Experimental conclusion: The darker the color of the solution, the more concentrated the solution.

[Experimental Study 2] Take the copper sulfate solution you just prepared and pour one solution into two empty test tubes. Add water to one of them, shake it, and observe the color.

Experimental phenomenon: The color becomes significantly lighter.

Experimental conclusion: Factors that affect the concentration of the solution are also the quality of the solvent.

In summary:

The quality of the solute and the quality of the solvent will affect the concentration of the solution.

1. Mass fraction of solute

Definition: The ratio of the mass of the solute to the mass of the solution

Expression: Mass fraction of solute =

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

Solution mass = Solvent mass + Solute mass

= solute mass ÷ solute mass fraction

= solution volume × solution density

The relationship between disaturated solutions, unsaturated solutions, concentrated solutions, and dilute solutions

1. Classification of solutions

(1) Based on whether a certain solute can continue to be dissolved, solutions are divided into: saturated solution; unsaturated solution.

(2) Based on the mass ratio of solute to solvent, solutions are divided into: concentrated solution; dilute solution.

2. The relationship between saturated solution, unsaturated solution and “concentrated” and “dilute” solutions

For example, at 20/℃, 20g NaCl is dissolved in 100g water, which can be said to be concentrated but not saturated;

At 20/℃, 0.153g Ca(OH)2 is dissolved in 100g of water, which is dilute but saturated.

Conclusion: A saturated solution is not necessarily a concentrated solution, and a dilute solution is not necessarily an unsaturated solution.

3. Calculation of solutions

1. Given the mass of solute and solvent, find the mass fraction of solute

[Calculation] Add 0.5g,

1g, 1.5g of solute, what is the mass fraction of the solute in the three solutions?

The mass fractions of solutes in the three solutions are:

1. The mass fraction of solute is: 0.5g/ 0.5g+10g×100% = 4.8%

2. The mass fraction of solute is: 1g/1g+10g×100% = 9%

3. The mass fraction of solute is: 1.5g/ 1.5g+10g×100% = 13%

Put 1g of table salt into the beaker, then add 9mL of water, and stir with a glass rod until dissolved. Then add 10 mL of water to the above beaker and stir (the density of water is 1 g·cm-3). Find: 1. Try to write down the solute mass, solution mass, and solute mass fraction before and after dilution. 2. Analyze the changes in each quantity.

Answer: 1. Before dilution

The mass of the solute before dilution is 1g.

The mass of the solution is 10g,

The mass fraction of solute is 10%

After dilution

The mass of the solute after dilution is 1g.

The mass of the solution is 20g,

The solute mass fraction is 5%

2. After dilution, the mass of the solution increases, the mass of the solute remains unchanged, and the mass fraction of the solute decreases.

Mass of solute before dilution = Mass of solute after dilution

Conclusion: The mass fraction of the solute is reduced by half, and the mass of water added is the same as the mass of the corresponding solution.

Example 1. The chemical laboratory currently has 98% concentrated sulfuric acid, and dilute sulfur is often needed in experiments.

acid solution. To dilute 50g of concentrated sulfuric acid with a mass fraction of 98% to a mass fraction of

How many grams of water are needed for 20% sulfuric acid solution?

Solution 1: Suppose the mass of water to be added is x

50g×98%=(50 + x)×20%

x=195g

Solution 2: Let the mass of the diluted solution be y

59g×98%=20%·y

y=245g

Water required: 245g-50g=195g

answer:--------.

Example 2. A factory laboratory prepares 5000g of 20% hydrochloric acid, which requires 38% of

How many milliliters of hydrochloric acid (density is 1.19g·mL-1)

Analysis: The mass fraction of a solute is a mass ratio, and the volume cannot be directly substituted into the formula for calculation. When it comes to volume:

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

Solution: Suppose the required volume of 38% hydrochloric acid is x

1.19g·mL-1·x·38%=5000g×20%

x = 2211mL

answer:---------.

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Update Time: 2024-07-28

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