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

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

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)

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

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:

-Halide: Cl-, Br-, I-, except for salts with Ag+, Hg22+, Pb+2

-Nitrate, NO3-

-Acetate, CH3CO2-

-Sulfate, SO42-, except for salts with Ba+2, Hg2

2+, Pb+2

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)

“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

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)

initial values final values

M1V1 = M2V2

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)

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

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)