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)

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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, Hg22+, 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)

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“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: •Solute particles are small •Solvent is heated •Solution is stirred

Concentration: Relationship between amount of solute contained in a specific amount of solution

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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

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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 initial values

M2V2 final values

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

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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

Example:

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

4% starch

H2O

10% starch

Eventually, the flow of water across the semi-permeable membrane becomes equal in both directions.

7% starch H2 O

7% starch

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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 (hypertonic)

Burst (hypotonic)

No Change (isotonic)

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