Properties of Solutions

15.2

Solvents and Solutes

An aqueous solution is water that contains dissolved substances.

the dissolving medium is the solvent.

the dissolved particles are the solute.

Solutions

Solutions = homogeneous mixtures In a solution, the solute is dispersed

uniformly throughout the solvent.

Why does a solution form?LIKE DISSOLVES LIKEPolar solvents (water)dissolve ionic compounds and polar compounds.

Nonpolar solvents (gasoline) dissolve nonpolar compounds.

15.2

Vitamin A is soluble in nonpolar compounds (like fats).

Vitamin C is soluble in water.

Which vitamin is water-soluble and which is fat-soluble?

How Does a Solution Form?• There are 3 ways a solution can form• 1. dissociation• 2. dispersion• 3. ionization

Dissociation The process which an ionic compound

separates into its ions as it dissolves is called dissociation

Physical change

DispersionWhen a solid breaks into small pieces and is spread throughout the solvent

Ex: lifesaver on your tongue

Physical change

Ionization of Molecular compounds The process in which neutral molecules

gain or lose electrons is known as ionization

Chemical change

Properties of liquid solutionsConductivityFreezing and boiling point

Conductivity When ionic compounds are dissolved in water they separate into ions and the solution is able to conduct electricity

Freezing Point and Boiling Point Adding a solute to water can increase

the boiling point of the solvent and decrease the freezing point of the solvent

Frozen frogs What about people?

Heat of Solution During the formation of a solution, heat

is either Absorbed- endothermic- bonds broken

(solute and solvent)

Released – exothermic- bonds formed between solute and solvent

In order for a solution to form attractions between the solute particles and attractions between the solvent particles must be broken- this requires energy- endothermic

When the new attraction is formed between the solute and solvent- energy is released- exothermic

SolubilityA saturated solution contains the maximum amount of solute for a given quantity of solvent at a given temperature and pressure.

An unsaturated solution contains less solute than a saturated solution at a given temperature and pressure.

16.1

Degree of saturation

Unsaturated Solution Less than the

maximum amount of solute for that temperature is dissolved in the solvent.

No solid remains in flask.

Degree of saturation

Supersaturated Solvent holds more solute than is normally

possible at that temperature. These solutions are unstable; crystallization

can often be stimulated by adding a “seed crystal” or scratching the side of the flask.

Solution FormationThe compositions of the solvent and

the solute determine IF a substance will dissolve.

The factors that determine the RATE which a substance dissolves are:

stirring (agitation)temperaturethe surface area of the

dissolving particles

16.1

Factors Affecting Rate of Solubility

Temperature The solubility of most solid substances increases as the temperature of the solvent increases.

The solubilities of most gases are greater in cold water than in hot.

16.1

Factors Affecting Solubility Pressure

Changes in pressure have little effect on the solubility of solids and liquids, but pressure strongly influences the solubility of gases.

Gas solubility increases as the partial pressure of the gas above the solution increases.

16.1

Gases in SolutionThe solubility of

liquids and solids does not change appreciably with pressure.

But, the solubility of a gas in a liquid is directly proportional to its pressure.

Increasing pressure above solution forces more gas to dissolve.

Factors Affecting the Solubility of Gases Solubility of most gases decreases as

temperature increases Gases tend to have weak intermolecular

forces Ex: N2 and O2 form weak dipole-induced dipole

forces and weak dispersion forces with water As the kinetic energy of particles within a

solution increases the gas particles break free from weak attractions and re-enter the gas phase

TemperatureThe opposite is true

of gases. Higher temperature drives gases out of solution.

Carbonated soft drinks are more “bubbly” if stored in the refrigerator.

Warm lakes have less O2 dissolved in them than cool lakes.

Temperature

Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

Factors Affecting Solubility

16.1

Factors Affecting Solubility of Gases Real life:

Warm soda goes flat faster than cold soda Fishing Thermal pollution The Bends

SolubilitySolubility is often expressed in grams of solute per 100 g of solvent.

16.1

Gases in Solution

In general, the solubility of gases in water increases with increasing mass.

Why?Larger molecules

have stronger dispersion forces.

Gases in Solution

Concentration of Solutions Percent by Volume

% by volume – volume of solute x 100 volume of solution

Concentration of Solutions Percent by Mass

% by mass = mass of solute x 100 mass of solution

Concentration of Solutions Molarity

Molarity = moles of solute moles of solution

Properties of Acids and Bases

Acid and Bases

Acid and Bases

Acid and Bases

Identifying Acids Acids – produce hydrogen ions (H+) in

solution – also known as hydronium ions H3O+

Properties of Acids Taste sour React with metals Change color in indicators React with carbonates Contain H+ ions

Acids React with Active Metals

Acids react with active metals to form salts and hydrogen gas:

HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

This is a single-replacement reaction

Acids React with Carbonates and Bicarbonates

HCl + NaHCO3

NaCl + H2O + CO2

Hydrochloric acid + sodium bicarbonate

salt + water + carbon dioxide

An old-time home remedy for relieving an upset stomach

Effects of Acid Rain on Marble(marble is calcium carbonate)

George Washington:BEFORE acid rain

George Washington:AFTER acid rain

Identifying bases Bitter taste Slippery feel Color changes in indicators Contain hydroxide ions OH -1

Changing indicator color

the flower color can be determined by the relative acidity of the soil: an acidic soil (pH below 6) will usually produce flower color closer to blue, whereas an alkaline soil (pH above 6) will produce flowers more pink. This is caused by a color change of the flower pigments in the presence of aluminium ions which can be taken up into hyperaccumulating plants.

Neutralization Acid + base → salt + water

HCl + NaOH → NaCl + H2O

A specific type of double replacement reaction

Proton donors and acceptors Acids can be defined as proton donors

Bases can be defined as proton acceptors

Ex:

Strengths of Acids and Bases pH scale – the lower the pH the greater

concentration of H+ ions in solution

The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion.

Under 7 = acid 7 = neutral

Over 7 = base

Strong vs weak Strong acids completely ionize in water

HCl → H+ + Cl –

Weak acids do not completely ionize in water HC2H3O2 → H+ + C2H3O2

- + HC2H3O2

Buffer Weak acids can be used to make buffers Buffer is resistant to large changes in pH

Buffer systems in your blood keep the pH of your blood within a narrow range

Buffers continued … Carbon dioxide dissolved in the blood

acts as an acid and forms carbonic acid when dissolved in water

Hydrogen carbonate produced in the kidneys is a base that soaks up the hydrogen ions when there are too many and transport them to the lungs where the acid is excreted as carbon dioxide

Electrolytes A substance that ionizes or dissociates

into ions when it dissolves in water

Can conduct electricity