Solubility of a Salt
Introduction: The solubility of a pure substance in a particular solvent is the quantity of that substance that will dissolve in a given amount of a solvent. Solubility varies with the temperature of the solvent. Thus, solubility must be expressed as quantity of solute per quantity of solvent at a specific temperature. For most ionic solids, especially salts, and water, solubility varies directly with the temperature. That is, the higher the temperature of the solvent (water), the more solute (salt) that will dissolve in it. In this experiment, we will study the solubility of potassium nitrate (KNO3) in water. You will dissolve different quantities of this salt in a given amount of water at a temperature close to its boiling point. Which solution will be
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Saturated- The solution is full and contains the maximum amount of dissolved solute for that given temperature. No more solute can be dissolved in the solvent. This condition can be represented by a point on the solubility curve.
Unsaturated- This is a solution in which more solute can be added and can still be dissolved. It has not reached a maximum yet for that temperature. This is a point that is underneath the solubility curve.
Supersaturated- This is a solution that contains more solute than the solvent can dissolve. This is any point above the solubility curve. A supersaturated solution is made by heating the solvent to a high temperature, dissolving the solute, and then slowly cooling it without presenting a seed to crystallize it.
Classify the following KNO3 solutions as saturated, unsaturated, or supersaturated. Explain your answer.
75 g KNO3/100 mL H2O at 40°C- supersaturated; At 40°C, the maximum amount of solute that can be dissolved in 100 mL of water is approximately 60 g of potassium nitrate. Dissolving 75 g will be more than what the solvent can dissolve, making it a supersaturated