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Exploring the limits of solubility and how physical conditions affect the saturation of a solution.
Have you ever wondered why a warm soda goes flat faster than a cold one, or how a single tiny crystal can turn a clear liquid into a solid mass of needles in seconds?
Solubility isn't just a limit; it's a balance. In an unsaturated solution, the solvent can still hold more solute. However, once you reach the saturated point, a dynamic equilibrium is established. At this stage, the rate at which the solute dissolves is exactly equal to the rate at which it recrystallizes. To the naked eye, nothing changes, but at the molecular level, particles are constantly moving between the solid and aqueous phases. A supersaturated solution is a fragile state where more solute is dissolved than theoretically possible at that temperature, often achieved by heating a solution and cooling it very slowly.
Quick Check
In a saturated solution with visible undissolved solid at the bottom, why does the mass of the solid remain constant despite particles still dissolving?
Answer
Because the rate of dissolution equals the rate of recrystallization, meaning for every particle that dissolves, another one returns to the solid state.
A solubility curve graphs the maximum amount of solute that can dissolve in of water across a range of temperatures. For most solids, solubility increases with temperature because the kinetic energy helps break the lattice energy of the crystal. If a saturated solution at a high temperature is cooled, the 'excess' solute can no longer stay dissolved and will fall out of the solution as a precipitate. By subtracting the solubility at the lower temperature from the solubility at the higher temperature, we can predict exactly how much solid will form.
A solution contains of in of water at . If the solubility at is and at it is , how much precipitate forms if the solution is cooled to ?
1. Identify initial state: The solution is unsaturated at because . 2. Identify final capacity: At , the water can only hold . 3. Calculate the difference: . 4. Result: of will precipitate.
The solubility of nitrogen in blood at is . If a diver breathes air at a total pressure of , what is the new solubility of nitrogen?
1. Set up the ratio: 2. Rearrange for : 3. Solve: 4. Conclusion: The solubility triples, which explains why rapid decompression can cause nitrogen bubbles to form in the blood (the 'bends').
Which of the following describes a supersaturated solution?
Increasing the temperature of a solvent generally decreases the solubility of gaseous solutes.
If the pressure of a gas over a liquid is doubled while temperature is constant, what happens to the solubility of the gas?
Review Tomorrow
In 24 hours, try to sketch a solubility curve for a typical solid and explain how to find the amount of precipitate if it is cooled from to .
Practice Activity
Look at a nutritional label for a carbonated drink and research why they use high-pressure CO2 during the canning process.