Solutions, Acids, and Bases

Chapter 7 & 8

Parts of a solution

Solute The substance that

is dissolved into the solution.

examples: • Sugar in kool-aid• Salt in salt water

• CO2 in soda

Solvent The substance that

does the dissolving in a solution.

examples:• Most common is

water.

Dissolving

Three ways to dissolve a solute in a solvent:

1. Dissociation

2. Dispersion

3. Ionization

1. Dissociation

The process in which an ionic compound separates into ions in a solution. (physical change)

Example: salt in water

2. Dispersion

Breaking the solute into small pieces and spreading throughout the solvent.

Ex. Sugar in waterPhysical change

3. Ionization

The process in which neutral molecules lose or gain electrons.

Chemical change

Conductivity

Many solutions can conduct an electric current if electrolytes are present. (ions)

Electrolytes = substances that will conduct an electric current when dissolved. Ex. NaCl, KCl, MgBr2

Freezing Point Depression

Lowering the freezing point of water by the addition of a solute

ex. salt. Used on icy roads in

winter Ice-cream

Boiling point elevation

The addition of a solute to a liquid solvent will usually raise the boiling point of the solvent.

Adding salt to boil water when cooking

Heat of Solution

A measure of the amount of energy either absorbed or released when a solute dissolves in a solvent.

Can be endothermic or exothermic.

Rate of Solution

Speed at which solute dissolves in a solvent.

1st Stirring the solution. Helps to move the solute particles away from the solid solute.

Other factors:

2nd : Powdering the solute.

Increases the surface area

3rd : Heating the solution.

Speeds up the molecules

Concentration

ConcentratedA large amount

of solute dissolved in a solvent

DiluteA little bit of

solute dissolved in a solvent

Saturation

A solution that contains all the solute it can possibly hold at a given temperature is said to be saturated.

Unsaturated = contains less solute than it can possibly hold

Supersaturated = a solution that holds more solute than it should at a given temperature.

Supersaturation example:

Sodium acetate in water.

Used in commercial hand warmers.

Insoluble

A substance that will NOT dissolve in water.

“Like dissolves like”

Nonpolar solvents will dissolve nonpolar solutes.

examples: benzene & acetone Polar solvents will dissolve polar solutes

2 factors that affect solubility:

1.Temperature Increase in temp

generally increases solubility of a solid in a liquid

Increase in temp decreases solubility of a gas in a liquid.

2. Pressure Usually has little, if

any, effect on solid and liquid solutes.

Increase in pressure increases the solubility of a gas in a liquid.

Specific concentration

Can be defined as percent by volume or percent by mass

Example: 3% hydrogen peroxide or 25% fruit juice.

MOLARITY

Acids

Very important chemicals in everyday life processes.

Properties of acids:

1. Sour taste (never taste a chemical)

2. All contain hydrogen

3. Also called “proton donors”

4. React with active metals to produce hydrogen gas.

Zn + 2HCl ZnCl2 + H2

Indicators

Chemicals used to identify acids and bases by changing color.

ACIDS:

A. Litmus paper (blue to red)

B. Phenolphthalein (colorless)

C. Methyl Orange (orange to red)

D. Bromothymol Blue (changes to yellow)

Common acids

Sulfuric (H2SO4) used in car batteries

Nitric (HNO3) used in fertilizers

Hydrochloric (HCl) stomach acid Carbonic (H2CO3) carbonated drinks

Acetic (HC2H3O2) vinegar

Bases

Also very important in everyday processes.

Properties of Bases:

Taste bitter; feel slippery Contain hydroxide (OH) ions. Known as “proton acceptors” Phenolphthalein turns bright pink Red litmus paper turns blue Bromothymol blue turns blue Methyl orange turns yellow

Common bases:

Sodium hydroxide NaOH making soap; drain cleaners

Potassium hydroxide KOH battery electrolyte

Calcium hydroxide Ca(OH)2 making plaster and drywall

Magnesium hydroxide Mg(OH)2antacids

Solutions of acids and bases

pH scale A numerical scale developed to

measure the relative strengths of acids and bases

Ranges from 0 to 14 0 is the strongest acid 14 is the strongest base.

What happens when an acid and a base combine? Always forms water and a salt. Salt = ionic compound formed when a

positive ion of a base combines with a negative ion of an acid.

Neutralization. These are double replacement

reactions.

What determines if an acid is classified as “strong” or weak? Strength is determined by how well the

acid or base dissociates into solution. Strong acids and strong bases are good

electrolytes.

Buffers

A mixture of a weak acid or weak base with its salt.

Resists large changes in pH.

Examples:– Bicarbonate ions in

your blood stream.