P R O P E R T I E S O F S O L U T I O N S

1. PROPERTIES OF SOLUTIONS 1. A solution is composed of: the solute: the minor component (least number of moles) the solvent: the major component (largest number of moles) 2. Soluble / Insoluble: A soluble substance readily dissolves in the solvent. An insoluble substance will NOT dissolve readily in a solvent. 3. Miscible / immiscible: Two liquids are miscible in each other if they readily mix to form a uniform solution. Two immiscible liquids will always separate out into two distinct layers. 4. Solubilitydescribes the amount of solute that will dissolve in a solvent. For example, 35.7 g of NaCl will dissolve in 100 mL of water at 0oC , no more.

2. PROPERTIES OF SOLUTIONS Factors which effectsolubility: 1. The size of the ions interacting 2. The charge of the ions interacting 3. Attractive and repulsive force interactions between ions 4. Intermolecular force interactions between solute and solvent. 5. Temperature 6. Pressure (for gas/liquid solutions)

3. General Solubility Rules for aqueous solutions Disclaimer: these rules do not address slightly soluble salts. 1. All Na+, K+, and NH4+ salts are soluble. 2. All NO3- and most C2H3O2- are soluble. 3. The Halides are soluble except Ag+, Hg22+, & Pb2+. 4. Sulfates are soluble except Ba2+, Sr2+, and Pb2+. 5. CO32-, PO43-, OH-, & S2- are insoluble except for those mentioned in #1.

4. PROPERTIES OF SOLUTIONS 5. Qualitatively solutions can be described as either dilute or concentrated. A dilute solution has a relatively small amount of solute while a concentrated solution has a relatively large amount of solute. There is generally no numeric value associated with these terms. For example a particular drink may be concentrated in sugar for one person’s taste but dilute in terms of another person’s preference.

5. PROPERTIES OF SOLUTIONS 6. A SATURATED solution occurs when the rate of dissolving of the solute (pink dots) into the solvent (blue dots) is in equilibrium with the rate of formation of the solute back into crystalline form. No more solute can be added without disturbing the equilibrium, resulting in the solute “falling” out of solution and crystal reformation is apparent. In this picture since the salt crystal is visible, the solution “saturated” with the solute. This solution has the maximum amount of solute dissolved. A salt crystal in water

6. PROPERTIES OF SOLUTIONS 7. In a SUPERSATURATED solution, the amount of solute dissolved in the solvent is beyond the saturated amount. This is possible by altering some physical conditions in order to “shift” the equilibrium so more solute can dissolve. For some substances, an increase in the temperature is one way to increase how much solute will dissolve in a given solvent. 204 g of sugar will dissolve in 100 g of water at 20oC but at 50oC you would be able to dissolve 260 g. If the 50oC saturated solution was allowed to cool to 20oC and if the sugar remained in solution then the solution is said to be supersaturated. This is usually an unstable situation and any disturbance to the cooled solution could cause the excess solute to “fall out” of solution as the 20oC saturation equilibrium is established.

7. FACTORS EFFECTING THE RATE OF DISSOLVING SOLIDS 1. Particle size: The smaller the particle size, the more surface area that is exposed thus the easier the solute dissolves. 2. Temperature: In many cases, temperature increases the rate of dissolving. 3. Concentration of solution: Dissolving is easier when there is less solute particles. The rate of dissolving decreases as the solution nears saturation. 4. Agitation: Stirring and swirling a solution increases the kinetic motion thus increases dissolving.

8. GENERAL PROPERTIES OF SOLUTIONS 1. A solution is a homogeneous mixture of two or more components. 2. It has variable composition. 3. The dissolved solute is molecular or ionic in size. 4. A solution may be either colored or colorless nut is generally transparent. 5. The solute remains uniformly distributed throughout the solution and will not settle out through time. 6. The solute can be separated from the solvent by physical methods.

9. PRACTICE PROBLEMS Short essay: • Can a saturated solution ever be a dilute solution? Explain. (answer on next slide) 2. Some drinks like tea are consumed either hot or cold but soft drinks are drunk only cold. Explain. 3. In a saturated solution containing undissolved solute, the solute is continuously dissolving, but the concentration of the solution remains unchanged. Explain.

10. Short essay answer: 1. Can a saturated solution ever be a dilute solution? Explain. Yes, a saturated solution can be dilute since the two terms do not correspond to each other. A saturated solution has the dissolved solute in equilibrium with undissolved solute, that is, all possible solute is already dissolved for that given temperature. A dilute solution contains a small amount of solute relative to the solvent. An example of a dilute solution that is saturated would be LiF in water, the solubility of LiF at 0oC is 0.12 g per 100 g of H2O therfore if you calculate the moles of solute: 0.12 g LiF (1 mol / 25.94 g) = 0.0046 mol of solute The moles of solvent is: 100 g ( 1 mol / 18 g ) = 5.55 mol of solvent Upon comparison, since the moles of solvent is 99.9% more than the moles of solute, one could argue that LiF is dilute relative to the solvent (Although still saturated).