Properties of Solutions

1. Properties of Solutions Solution: Homogenous mixture of 2 or more substances; particles are small (transparent) Colloid: Homogenous mixture of 2 or more substances; particles are larger (opaque) Solutions can be liquid, solid or gaseous Examples: Ocean, sugar water Gold alloy Air, humid oxygen

2. Solvent: Substance present in a solution in the greatest amount Example: Water in the ocean; nitrogen in air Solute: Substance present in a solution in lesser amounts than the solvent Example: Salt in ocean; oxygen in air Solutes can be electrolytes or nonelectrolytes Electrolytes: solutes that dissociate in solution into ions that carry charge (ionic compounds) Nonelectrolytes: solutes that do not dissociate in solution, and do not carry any charge

3. Solubility Soluble substance: Substance that is able to dissolve in a solvent Insoluble substance: Substance that does not dissolve in a solvent Solubility: Maximum amount of solute that can be dissolved in a specific amount of solvent under specific conditions of temperature and pressure (g solute/100 mL solution)

4. Saturated Solution: Solution containing maximum amount of solute that will dissolve under current conditions • Unsaturated Solution: Solution containing less than the maximum amount of solute that will dissolve under current conditions • Supersaturated Solution: Unstable solution containing amount of solute greater than the solubility value

5. General Rules for the Solubility of Ionic Compounds • A compound is soluble if it contains one of the following cations: • -Group 1A cations: Li+, Na+, K+, Rb+, Cs+ • -Ammonium, NH4+ • A compound is soluble if it contains one of the following anions:

6. Solubility of Solids and Liquids vs. Gases • Solubility of liquids and solids in water increases with increasing temperature • Example: More sugar will dissolve in warm water than in cold water • Solubility of gases in water decreases with temperature • Solubility of gases in water increases with increasing pressure (Henry’s Law)

7. “Like dissolves like:” • polar solvents will dissolve polar solutes • nonpolar solvents will dissolve nonpolar solutes • Examples: wax in CCl4, sugar in water; oil in water? • Solutes fail to dissolve when: • 1) forces between solute particles out-weigh attractions between solute and solvent • 2) solvent particles are more attracted to each other than to solute

8. Examples of Like Dissolves Like SolventsSolutes Water (polar) Ni(NO3)2 (ionic) CH2Cl2 (nonpolar) I2 (nonpolar)

9. Solutes dissolve faster when: Concentration: Relationship between amount of solute contained in a specific amount of solution • Solute particles are small • Solvent is heated • Solution is stirred

10. Concentration as Percent • Percent: Solution concentration giving the amount of solute in 100 parts of solution • % = part/total x 100 • Weight/weight percent: Concentration giving the mass of solute in 100 mass units of solution • %(w/w) = solute mass/solution mass x 100 • Example: 12.0%(w/w) sugar solution • 12 g sugar per 100 g solution

11. Weight/volume percent: Concentration giving the grams of solute contained in 100 mL of solution • %(w/v) = grams solute/mL solution x 100 • Example: 12.0%(w/v) sugar solution • 12 g sugar per 100 mL solution

12. Molarity: Unit of concentration used with solutions; number of moles of solute per liter of solution • Molarity (M) = moles of solute/liters of solution • Examples: 2 moles of NaCl dissolved in 1 L of water • M = 2 moles/1 L = 2 M • 1.5 moles NaCl dissolved in 2 L of water: • M = 1.50 moles/2.00 L = .750 M

13. Dilution Dilution: addition of solvent to decrease theconcentration of solute. The solution volume changes,but the amount of solute is constant. moles of solute (mol) = molarity (M) x volume (V) M1V1 = M2V2 initial values final values

14. M1 V1 =M2 V2 • Practice Problem: Prepare 250 mL of 0.100 M NaCl solution from a 2.00 M NaCl solution. • M1 = molarity of starting solution (in this case 2.00M NaCl) • V1 = volume of starting solution required (always unknown) • M2 = molarity of final solution after dilution (in this case 0.100M NaCl) • V2 = volume of final solution, after dilution (in this case 250ml)

15. Prepare 250 mL of 0.100 M NaCl solution from a 2.00 M NaCl solution. • M1 = molarity of starting solution (in this case 2.00M NaCl) • V1 = volume of starting solution required (always unknown) • M2 = molarity of final solution after dilution (in this case 0.100M NaCl) • V2 = volume of final solution, after dilution (in this case 250ml) • M1 V1 =M2 V2 • V1 = M2 V2 / M1 • V1 = (0.100M) x (250 ml) / (2.00M) = 12.5ml

16. Osmotic Pressure Osmosis: Movement of water through a semipermeable membrane, from more dilute solution towards more concentrated solution Osmotic pressure: amount of pressure required to stop flow of water due to osmosis Isotonic solutions: solutions with identical osmotic pressure; no urge for water to flow

17. Example: During osmosis, water flows across the semi-permeable membrane from the 4% starch solution into the 10% solution. 4% starch 10% starch H2O

18. Eventually, the flow of water across the semi-permeable membrane becomes equal in both directions. 7% starch 7% starch H2O

19. Hypotonic solution: the more dilute of 2 solutions separated by a semipermeable membrane; water leaves this solution and flows across membrane to the more concentrated solution Hypertonic solutions: the more concentrated of 2 solutions separated by a semipermeable membrane; water enters this solution, moving across the membrane from the more dilute solution Crenate Burst No Change (hypertonic) (hypotonic) (isotonic)