Unit 10 - Solubility

1. Unit 10 - Solubility Water & Solutions

2. I. Water – the universal solvent Surface Tension –inward force, or pull, that tends to minimize the surface area of a liquid Surfactant –wetting agent such as soap that decreases surface tension Hydrogen Bond – small attraction between the (+) hydrogen and (-) oxygen ends of water molecules

3. Atypical Ice Open framework arranged like a honeycomb. Framework collapses, molecules packed closer together, making it more dense

4. II. The Solution Process Solute - substance being dissolved Solution - homogeneous mixture Solvent - dissolving medium First... 1st solute particles are surrounded by solvent particles Then... 2nd solute particles are separated and pulled into solution

5. NONPOLAR NONPOLAR POLAR POLAR “Like Dissolves Like” Polar solvents dissolve polar molecules and ionic compounds Nonpolar solvents dissolve nonpolar compounds “Polar Dissolves Polar”

6. A. Electrolytes – compounds that conduct an electric current in solutions III. Electrolytes • All ionic compounds are electrolytes • Compounds that don’t conduct an electric current are called nonelectrolytes – not composed of ions, includes many molecular compounds (covalent bonds)

7. - + - - + + acetic acid salt sugar Non- Electrolyte Weak Electrolyte Strong Electrolyte solute exists as ions and molecules solute exists as ions only solute exists as molecules only solute exists as ions and molecules solute exists as ions only solute exists as molecules only

8. IV. Heterogeneous Systems Suspensions – mixtures from which particles settle out upon standing and the average particle size is greater than 100 nm in diameter. • Clearly identified as two substances • Gravity or filtration will separate the particles Colloids – heterogeneous mixtures containing particles that are between 1 nm and 100 nm in diameter • Appear to be homogeneous but particles are dispersed through medium • Ex: paint, aerosol spray, smoke, marshmallow, whipped cream Tyndall Effect -phenomenon observed when beam of light passes through a colloid or suspension • Colloids exhibit the Tyndall effect

9. IV. Solubility SATURATED SOLUTION max amount no more solute dissolves SUPERSATURATED SOLUTION over max amount becomes unstable, crystals form UNSATURATED SOLUTION capable of dissolving more solute • Supersaturated solutions are not in equilibrium with the solid substance and can quickly release the dissolved solids. • Saturated solution is one that is in equilibrium with respect to the dissolved substance. These conditions can quickly change with temperature. Concentration Increasing

10. Factors Affecting Solubility Stirring (agitation) - Increases solubility b/c if fresh solvent is brought in contact with the surface of the solute Temperature - Increases solubility by increasing kinetic energy, which increases the collisions b/w molecules of solvent and the surface of the solute Surface Area - A smaller particle size dissolves more rapidly than larger particles size (Surface phenomenon - More surface area exposed, faster rate of dissolving)

11. V. Solubility defined as the maximum grams of solute that will dissolve in 100 g of solvent at a given temperature Gases are more soluble at… low temperatures or high pressures (Henry’s Law). EX: the “bends” & soda Solubility Curve • shows the dependence of solubility on temperature • Note: the solubility of the gases are greater in cold water than in hot water • Solids are more soluble at... • high temperatures. When opened partial pressure of CO2 liquid decreases and the concentration of dissolved CO2 decreases.

12. VI. Concentrations of Solutions Concentrationof a solution is a measure of the amount of solute that is dissolved in a given quantity of solution. Dilute solution – contains a low concentration of solute. Concentrated solution –contains a high concentration of solute. Molarity (M) –number of moles of a solute dissolved per liter of solution (molar concentration) Molarity (M) = moles of solute liters of solution