Estudo das Soluções - 04 Calculando com Coeficiente de Solubilidade

Summary

In this educational video, the presenter teaches viewers how to calculate solubility and understand different types of solutions, such as unsaturated, saturated, and supersaturated. Using practical examples involving salts and their solubility at various temperatures, the video walks through step-by-step calculations to determine the maximum amount of salt that can dissolve in water. The script also explores how temperature changes affect solubility, with a focus on understanding when precipitates form. Viewers are encouraged to grasp these concepts to solve similar problems through proportional reasoning and rule-of-three calculations.

Takeaways

• 😀 Solubility is the maximum amount of a substance that can dissolve in a solvent at a given temperature.
• 😀 The solubility of a salt can change with temperature, and calculating it requires understanding the solubility coefficient.
• 😀 In the first example, a 350g amount of water dissolves a maximum of 105g of salt, and the solution formed is saturated when 70g of salt is added.
• 😀 A solution is considered saturated when the maximum amount of solute has dissolved in the solvent, and any extra solute will remain undissolved.
• 😀 In the second example, the solubility of silver nitrate increases with temperature, indicating it is an endothermic dissolution process.
• 😀 A solution prepared at a higher temperature (35°C) can form a precipitate if cooled down, as the solubility decreases with temperature.
• 😀 By calculating the difference between the solubility at different temperatures, you can determine the amount of precipitate formed.
• 😀 When preparing solutions, use the correct formula for solubility based on the volume of solvent (e.g., 36g of solute in 100mL of water).
• 😀 Precipitation occurs when the solute exceeds the maximum solubility for the given temperature, leading to undissolved solids.
• 😀 In the third example, the solubility of potassium chromate is calculated, and the solution's state is determined based on the amount of solute added to a fixed volume of solvent.

Q & A

What is the solubility coefficient mentioned in the script?

The solubility coefficient refers to the amount of a substance (salt) that can dissolve in a certain amount of solvent (water) at a specific temperature. For example, 30 grams of salt can dissolve in 100 grams of water at a temperature of 42°C.

How is the saturation of a solution determined?

Saturation is determined by comparing the amount of solute dissolved in a solvent to the maximum solubility of the solute at a given temperature. If the amount of solute equals the solubility coefficient, the solution is saturated.

What happens when you add more solute than the saturation point?

When more solute is added than the saturation point allows, the excess solute will not dissolve and will form a precipitate, indicating that the solution is supersaturated.

What was the solubility of the salt in the first example when 350 grams of water was used?

In the first example, the maximum amount of salt that could dissolve in 350 grams of water at 42°C was 105 grams, based on the solubility coefficient of 30 grams per 100 grams of water.

What type of solution was formed when 70 grams of salt was added to 350 grams of water?

Since 70 grams of salt is less than the maximum dissolvable amount (105 grams), the solution was considered saturated, meaning no more solute could dissolve.

How does temperature affect solubility in the case of silver nitrate (AgNO3)?

Temperature increases the solubility of silver nitrate. The script states that at 25°C, the solubility is 36 grams per 100 mL of water, but at 35°C, the solubility increases to 55 grams per 100 mL.

What happened when a solution of silver nitrate prepared at 35°C was cooled to 25°C?

When the solution was cooled, the solubility of silver nitrate decreased, leading to the formation of a precipitate as excess solute could no longer remain dissolved in the solvent.

What is the formula for calculating the mass of solute that can dissolve in a given volume of solvent?

To calculate the mass of solute that can dissolve in a given volume of solvent, you can use the formula: Mass = (Solubility Coefficient × Volume of solvent) / 100. For example, if the solubility is 36 grams per 100 mL, in 200 mL, you can dissolve 72 grams of solute.

How do you calculate whether a solution is saturated, supersaturated, or unsaturated?

You compare the amount of solute dissolved in the solvent to the solubility coefficient at the given temperature. If the amount of solute is equal to the solubility coefficient, the solution is saturated. If more solute is added than can dissolve, it is supersaturated. If less solute is present than the maximum, it is unsaturated.

What was the precipitate formation in the third example involving potassium chromate?

In the third example, after agitating and mixing different amounts of potassium chromate with 20 mL of water, it was determined that solutions with more than 2.5 grams of solute formed precipitates. The solutions with 3 grams, 5 grams, and 7 grams had precipitates due to exceeding the solubility limit of 2.5 grams per 20 mL.