A KCl solution containing 42g of KCl per 100.0 g of water is cooled from 60 C to 0 C . What will happen during cooling?
Since the solubility of KCl is about 45 g at 60 ∘C, a KCl solution containing 42 g in 100 g of water at 60∘C is holding less solute than possible at that temperature and is unsaturated. The solubility of KCl is about 27 g at 0 ∘C, so a KCl solution containing 42 g in 100 g of water at 0 ∘C is holding as much solute as possible at that temperature and is saturated. Therefore, the excess solute will precipitate as the solution cools.
Answer Requested
The amount that precipitates should be the difference between the mass of KCl
present initially and the solubility value for KCl at 0 ∘C:
mass precipitate=(initial dissolved mass)−(solubility at 60∘C)=42g−27g=15gKCl precipitates
Well, during the cooling process, the KCl solution will start feeling a bit "chilled" out. It'll become cooler and cooler as the temperature drops from 60°C to 0°C. You might even see some "cool crystals" forming as the KCl becomes less soluble in the colder water. Just make sure it doesn't turn into one icy cold KCl popsicle – that wouldn't be very refreshing!
During the cooling of the KCl solution, several things will happen:
1. The temperature of the solution will decrease from 60°C to 0°C.
2. As the temperature decreases, the solubility of KCl in water will decrease. This means that the KCl will start to come out of the solution and form solid crystals.
3. The formation of solid crystals will result in the solution becoming more concentrated with KCl.
4. Eventually, at or near the freezing point of the solution, the solubility limit of KCl will be reached, and no more KCl will be able to dissolve.
5. As the cooling continues, more and more KCl will solidify, resulting in the formation of a KCl crystal lattice within the solution.
6. The solution will become supersaturated, meaning that it contains more solute (KCl) than it can hold at that temperature.
7. The excess KCl will continue to crystallize, eventually resulting in the separation of solid KCl crystals from the remaining liquid.
8. The final result will be a mixture of solid KCl crystals suspended in a smaller volume of liquid, which will be more concentrated in KCl compared to the original solution.
During the cooling process, the KCl solution will undergo several changes:
1. Decrease in temperature: The KCl solution is initially at 60°C, and as it is cooled, the temperature will decrease gradually.
2. Crytallization: As the temperature drops, the solubility of KCl in water decreases. At a certain temperature, known as the solubility limit, the excess KCl in the solution will start to form crystals. This is because the cooler temperature reduces the kinetic energy of the molecules, and they have less energy to overcome the attractive forces holding them together, resulting in the formation of solid KCl crystals.
3. Increase in concentration: As KCl crystals form, the amount of KCl dissolved in the water decreases. However, since the amount of water remains constant, the concentration of KCl in the solution increases. This is because the dissolved KCl is "trapped" in the liquid phase, while the solid KCl is separated out.
4. Supercooling: In some cases, the KCl solution can be cooled below the solubility limit without crystallization occurring immediately. This is called supercooling, where a solution remains in a liquid state even though it is below the temperature at which it would normally freeze. Supercooling can occur due to the absence of impurities or nucleation sites in the solution that would facilitate crystal formation.
Overall, as the KCl solution is cooled from 60°C to 0°C, the temperature decreases, KCl crystals begin to form, the concentration of KCl in the solution increases, and there can be a possibility of supercooling before crystallization occurs.