"Concentration of Solution" Solution PPT Courseware 6

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"Concentration of Solution" Solution PPT Courseware 6

Concentrated and dilute solutions

Correctly understand "concentrated" and "dilute" solutions

Summary: For colored solutions, whether the solution is concentrated or dilute can be distinguished based on the depth of the color.

1. Whether a solution is saturated or not is not necessarily related to the concentration or dilution, that is, a concentrated solution is not necessarily a saturated solution, and a dilute solution is not necessarily an unsaturated solution.

2. At the same temperature, for solutions of the same substance, the saturated solution is more concentrated than the unsaturated solution.

3. Concentrated and dilute solutions cannot accurately represent the amount of solute in a certain amount of solution. For practical applications, it is often necessary to know exactly the amount of solute in a certain amount of solution - that is, an exact representation of the solution's composition.

4. There are many ways to express the composition of a solution. The mass fraction of the solute in the solution is usually used to express the composition of the solution.

1. Mass fraction of solute

1. Definition: Ratio of solute mass to solution mass

2. Formula: Mass fraction of solute = mass of solute (g)/mass of solution (g) × 100%

=Mass of solute (g)/Mass of solute (g)+Mass of solvent (g)×100%

Solute mass = solution mass × solute mass fraction

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

3. Calculation of solute mass fraction

Example 1: Pour half of 20g of 10% salt water into the solution. Find the mass fraction of the solute in the remaining solution.

The solute mass fraction of the remaining solution remains unchanged, still 10%

Example 2: Take 35g of the solution from a bottle of potassium chloride and evaporate it to dryness to obtain 7g of potassium chloride solid. Find the mass fraction of the solute in this bottle of solution.

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

=7g/35g×100%=20%

Answer: The mass fraction of potassium chloride in this bottle of solution is 28.6%

2. Preparation of solution

(1) Experimental steps:

1. Calculate 2. Weigh, measure 3. Dissolve 4. Bottle

Example 1: (The solute is solid) Prepare 50g of 6% salt water

1. Calculation: 50g x 6% = 3g of salt required

Water required 50g–3g=47g 47g÷1g/mL= 47mL

2. Weighing: Use a balance to weigh 3g of salt. Measure: Use a graduated cylinder to measure 47mL of water.

3. Dissolve: Stir with a glass rod to completely dissolve

4. Bottle: (Cap the bottle and label it)

(2) Experimental instruments:

Medicine spoon, pallet balance, measuring cylinder, plastic tip dropper, beaker, glass rod

Reasons for the small solute mass fraction of the solution:

1. The balance is used incorrectly, such as medicines and weights are placed upside down (use weights when weighing), causing the weighed weight of medicines to be too small.

2. When measuring water, look up at the reading to avoid taking too much water.

3. The beaker is not dry. There is some water inside.

4. Solid medicines contain impurities, etc.

Reasons for the large solute mass fraction of the solution:

1. The balance is used incorrectly. If the balance is not adjusted before weighing, the pointer will be to the right, resulting in over-weighing of the medicine.

2. The weights are rusty.

3. When measuring water, you look down at the reading, which causes the amount of water to be taken out.

4. When pouring the water from the measuring cylinder into the beaker, part of it is sprinkled outside, etc.

Operation

1. Put 6g of iron sample into 100g of dilute sulfuric acid. After the reaction stops, 0.2g of hydrogen is generated. What is the mass fraction of the solute in the solution obtained after the reaction?

2. Put 12.5g of limestone sample into 100g of dilute hydrochloric acid. After the reaction stops, the total mass of the remaining material is 108.1g. Find the mass fraction of the solute in the solution obtained after the reaction?

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Update Time: 2024-11-19

This template belongs to Chemistry courseware People's Education Press Ninth Grade Chemistry Volume 2 industry PPT template

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