Problem 109 - Chemistry Matter and Change

Question

If you prepared a saturated aqueous solution of potassium chloride at \(25^{\circ} \mathrm{C}\) and then heated it to \(50^{\circ} \mathrm{C},\) would you describe the solution as unsaturated, saturated, or supersaturated? Explain.

Step-by-Step Solution

Answer

The solution would be described as unsaturated at 50°C. This is because the solubility of KCl increases with temperature, and when we heat a saturated solution of KCl from 25°C to 50°C, the amount of KCl that can be dissolved in water increases. Thus, the solution can dissolve additional KCl and is no longer saturated.

Step 1: Understand the solubility of KCl at different temperatures

First, we need to investigate how the solubility of potassium chloride changes with temperature. Check a solubility graph or a table with values of KCl solubility at various temperatures.

Step 2: Determine the solubility at 25°C and 50°C

From a solubility graph or table, find the solubility of KCl at 25°C and 50°C. For instance, we can find that the solubility of KCl at 25°C is approximately 34 grams per 100 grams of water, and the solubility at 50°C is approximately 48 grams per 100 grams of water.

Step 3: Compare solubility at 25°C and 50°C

By comparing the solubility at 25°C (34 grams per 100 grams of water) and 50°C (48 grams per 100 grams of water), we can see that the solubility increases with temperature. This means that at 50°C, water can dissolve more KCl than it could at 25°C.

Step 4: Determine the state of the solution

Since we started with a saturated solution at 25°C and then heated it to 50°C, increasing the amount of KCl that can be dissolved in water, the solution would no longer be saturated at 50°C. Instead, it would become unsaturated, as it now has the capacity to dissolve additional KCl. In conclusion, if we prepare a saturated aqueous solution of potassium chloride at 25°C and then heat it to 50°C, the solution would be described as unsaturated.

Key Concepts

Saturated Solution

In the world of chemistry, a saturated solution is an intriguing concept. This type of solution contains the maximum amount of solute that can be dissolved in a solvent at a particular temperature and pressure. Essentially, it means that the solution has reached its full capacity of solute, leaving any additional material unable to dissolve.
In practical terms, think of it like putting sugar in tea; once the solution is saturated, any extra sugar will simply settle at the bottom. The saturation point varies depending on the substances involved. For example, at a certain temperature, water can only dissolve so much potassium chloride (KCl) before becoming saturated.

• Defines the limit of solubility at a given condition
• No more solute can be dissolved
• Directly influenced by temperature and pressure

Thus, if you have potassium chloride dissolved in water to its maximum solubility at 25°C, the solution is saturated.

Unsaturated Solution

An unsaturated solution is like a glass half full. It means that the solution contains less solute than what is needed to saturate it. In other words, there's room for more solute to dissolve.
This happens often in everyday life. Suppose you add a spoonful of salt to a pot of water, but the salt quickly dissolves—this is an unsaturated solution. There is potential for even more salt to be added and dissolved into the water.

• Still has capacity to dissolve more solute
• Under the saturation level
• Can become saturated if more solute is added

Returning to our potassium chloride example, if the solution is saturated at 25°C and then heated to 50°C, the increased temperature means it can dissolve more KCl. Therefore, it transitions to being unsaturated, as there is now spare capacity for additional solute to dissolve.

Temperature Effect on Solubility

Temperature has a fascinating impact on solubility, often dictating how much of a substance can be dissolved in a solvent. When you increase the temperature, the solubility of solids in liquids generally increases. This is because higher temperatures provide the energy needed to break bonds in the solute, allowing more of it to dissolve.
For example, when heating a saturated potassium chloride solution from 25°C to 50°C, you are increasing the capacity of the solvent (water in this case) to dissolve more potassium chloride. This is why the once saturated solution becomes unsaturated at the higher temperature.

• Higher temperatures often lead to greater solubility for solids
• Energy from heat helps dissolve more solute
• Solubility can vary greatly between different substances

Understanding this concept is crucial in fields like cooking, chemistry, and industrial processes, where temperature control can enhance the dissolution rates significantly.