Properties of Solutions
Solution: Homogenous mixture of 2 or more substances
Solutions can be liquid, solid or gaseous
Examples: Ocean, sugar water
Gold alloy
Air, humid oxygen
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
Colloid: Homogenous mixture of 2 or more substances in which the substances are larger than those in solutions
Suspension: Heterogeneous mixture, with very large particles capable of settling out of solution
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
Saturated Solution: Solution containing maximum amount of solute that will dissolve under current conditions
Supersaturated Solution: Unstable solution containing amount of solute greater than the solubility value
Solubility of liquids and solids in water typically 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)
“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
Examples of Like Dissolves Like
Solvents Solutes
Water (polar) Ni(NO3)2
(ionic)
CH2Cl2 (nonpolar)
I2 (nonpolar)
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
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
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
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
Preparing Solutions
Measure proper amount of solute into container, then add solvent to proper volume.
Example: 1 L of 1.50 M CoCl2 Solution
M = moles/Liter M x Liter = moles
1.5 moles/L x 1L = 1.5 moles needed
1.5 moles CoCl2 = 195g CoCl2
1.5 mol CoCl2 x 130 g CoCl2/mol = 195g CoCl2
Place 195 g CoCl2 in a flask. Add water to fill to 1-L mark
Dilute a more concentrated solution with solvent to give a solution of lower concentration.
M1 V1 =M2 V2
Example: 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)
Use M1 V1 = M2 V2 to solve for the unknown variable (V1); this is the amount of the starting solution you need. Add solvent (usually water) to reach the desired total volume (V2).
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)
Answer: Prepare solution by adding 0.0125 L of 2.0 M NaCl to flask and adding water up to 250 mL mark.
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
4% starch
10% starch
H2O
Example:
During osmosis, water flows across the semi-permeable membrane from the 4% starch solution into the 10% solution.
Eventually, the flow of water across the semi-
permeable membrane becomes equal in both directions.
7% starch
7% starch
H2O
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)
Practice with Molarity
Calculate the molarity of 1.50 L of solution containing 0.294 moles of solute
Calculate the molarity of 500 mL of solution containing 0.304 moles of solute
Calculate the molarity of a 100 mL solution containing 4 g of NaOH.
How would you make 100 mL of 0.25 M Na2SO4 solution?
How would you prepare 5 L of 6 M H2SO4 from 18 M H2SO4 solution?