A solution is prepared by dissolving 12.5 g of KBr in 20 mL of wa...

Question

A solution is prepared by dissolving 12.5 g of KBr in 20 mL of water at 60 °C (see Figure 9.3). Is this solution saturated, unsaturated, or supersaturated? What will happen if the solution is cooled to 10 °C?

Graph showing solubility of KBr and other salts in water at varying temperatures.

Accepted Answer

Welcome back everyone. At 50 degrees Celsius, 16.4 g of potassium chloride is dissolved in 100 mL of water. The solution is then cooled to 20 degrees Celsius is the solution unsaturated, saturated or supersaturated. In the new temperature. Below, we are given a graph of solubility of various substances. One of them which include our focused substance being potassium chloride. Now this is going to be the solute and it's dissolved in 100 g of water where on the y axis of this graph is recorded the solubility values for each of these substances in different solutions. And then we have temperature and Celsius on the X axis. From the prompts. We're told that the solubility of the mass of potassium chloride is at 50 degrees Celsius. So let's determine what that solubility value would be starting at 50 degrees Celsius and traveling until we hit the curve, we would observe that the solubility of potassium chlorate at that temperature, 50 Celsius is about maybe we'll say about 21 g and recall that solubility is typically going to be a single value for a given substance at a cer certain temperature. But then we have concentration that we can express in terms of either moles of solute per liter of solution or we can express concentration as weight of solute by volume of solution. In this case of our example, grams per milliliter. However, we should express volume in liters typically. So for the concentration we're told we have a mass of potassium chloride being used of 16.4 g. And this is out of 100 mL of solvent. Let's recall the following. When the concentration of solute is less than its solubility then recall that this correlates to an unsaturated solution. So there is more solute available to be dissolved and this will favor the solution of the solute within the solvent. Next, let's recall that when the concentration of the solute is equal to its solubility, then the solution is considered saturated. So we have a saturated solution and for a saturated solution recalled that the solute is an equilibrium between its aqueous phase and solid phase. So third, let's recall that when the concentration of our solute is greater than its solubility that would correlate to the solution. Now being super saturated and recall a supersaturated solution favors precipitates. So with all of this outlined, let's now go back to the fact that given the solubility of potassium chloride, this will represent the most solute that can be dissolved at a given temperature versus concentration, which just gives us a figure of how much solute the substance being dissolved that is available in the solution. So given that we are told that the temperature is then cooled to degrees Celsius for the solution. If we know we have 16.4 g of solute, let's see where that responds to on the graph starting at Celsius and traveling to 16.4 g. We'll say that's around this location that correlates to being above the solubility curve of potassium chloride. So let's make a marker there. So we can make a note that since at 20 degrees Celsius, given the mass of potassium chlorate, that position on the graph correlates to the concentration of potassium chlorate being greater than the solubility curve greater than its solubility based on what we outlined that correlates to the solution being super saturated. So precipitation will be favored and the solution can crystallize. And so our final answer is that decreasing, the temperature is going to lower the maximum solubility of potassium chloride. So the solution will now be super saturated in the new cooler temperature of 20 Celsius. This is our final answer. I hope this made sense and let us know if you have any questions.

A solution is prepared by dissolving 12.5 g of KBr in 20 mL of water at 60 °C (see Figure 9.3). Is this solution saturated, unsaturated, or supersaturated? What will happen if the solution is cooled to 10 °C?

Key Concepts

Solubility

Saturated, Unsaturated, and Supersaturated Solutions

Temperature Effects on Solubility

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