Estudo das Soluções: 06 Calculando com Curvas de Solubilidade

Summary

In this educational video, the instructor guides viewers through calculating solubility using solubility curves. The lesson covers essential topics such as the effect of temperature on solubility, calculating the minimum amount of water needed to dissolve a given amount of salt, and understanding how solubility changes with temperature. Practical examples are used to demonstrate how to calculate solubility at different temperatures, determine the maximum amount of solute that can dissolve, and assess the formation of precipitates when a solution cools. The content is designed to help viewers apply these concepts to solve real-world chemistry problems.

Takeaways

• 😀 The video introduces how to use solubility curves for calculations in solution chemistry.
• 😀 The script explains how to determine the minimum amount of water needed to dissolve a certain amount of salt, using solubility data from graphs.
• 😀 Solubility curves can be exothermic, meaning that the solubility decreases as the temperature rises, as discussed for salt A.
• 😀 At 10°C, the solubility of salt A is 80 grams per 100 grams of water.
• 😀 To dissolve 16 grams of salt A at 10°C, 20 grams of water are required, based on the solubility data.
• 😀 A graph shows how solubility varies with temperature, and this information is crucial for calculating how much salt can dissolve in a given amount of water at specific temperatures.
• 😀 At 60°C, the solubility of a salt (e.g., salt B) is higher, and the amount of salt that can dissolve in 250 grams of water is 225 grams.
• 😀 When the temperature is 60°C, to dissolve 15 grams of salt B, you would need 25 grams of water.
• 😀 The script covers how cooling a saturated solution causes precipitation of excess solute. An example with ammonium chloride (NH4Cl) shows how cooling from 70°C to 30°C results in precipitate formation.
• 😀 The video emphasizes the importance of understanding solubility data to make accurate calculations for dissolving salts in water at different temperatures.

Q & A

What is the solubility curve used for in this video?

The solubility curve is used to determine how the solubility of a substance changes with temperature, allowing calculations for how much solute can dissolve in a given amount of solvent at specific temperatures.

How do you calculate the minimum amount of water needed to dissolve a given mass of solute?

To calculate the minimum amount of water, you need to know the solubility of the solute at the given temperature. Then, use the ratio of solubility (grams of solute per 100 grams of water) to determine how much water is required to dissolve the given mass of solute.

In the first example, how much water is needed to dissolve 16 grams of salt at 10°C?

At 10°C, the solubility of the salt is 80 grams per 100 grams of water. To dissolve 16 grams of salt, you would need 20 grams of water.

What is the significance of the solubility curve being described as 'exothermic' in the video?

The term 'exothermic' refers to the fact that the solubility of the salt decreases as the temperature increases, meaning heat is released as the solute dissolves in the solvent.

How do you calculate the maximum amount of solute that can dissolve in a specific mass of water?

To calculate the maximum amount of solute that can dissolve, you use the solubility value at the given temperature. Multiply the solubility (grams of solute per 100 grams of water) by the amount of water available and divide by 100.

What is the maximum amount of solute that can dissolve in 250 grams of water at 60°C?

At 60°C, the solubility is 90 grams per 100 grams of water. To dissolve in 250 grams of water, you can dissolve 225 grams of solute.

In the second example, how do you find the amount of water needed to dissolve 15 grams of salt at 60°C?

At 60°C, the solubility of the salt is 60 grams per 100 grams of water. To dissolve 15 grams of salt, you need 25 grams of water, which can be calculated by the proportion 15/60 = x/100.

What happens when a saturated solution is cooled?

When a saturated solution is cooled, the solubility of the solute decreases, and excess solute will precipitate out of the solution, forming solid crystals.

How much solute will precipitate if a saturated solution of ammonium chloride is cooled from 70°C to 30°C?

At 70°C, the solubility of ammonium chloride is 60 grams per 100 grams of water. At 30°C, the solubility decreases to 40 grams per 100 grams of water. If the solution contains 200 grams of water, 40 grams of solute will remain dissolved, and 120 grams will precipitate out.

Why is it important to use solubility curves when solving problems involving different temperatures?

Solubility curves show how the solubility of a solute changes with temperature, allowing for accurate calculations of how much solute can be dissolved at different temperatures, which is crucial for understanding saturation points and precipitation.