Solutions, Acids, and Bases

Chapter 7

Parts of a solution

SoluteThe substance that is dissolved into the

solution.examples:

• Sugar in kool-aid• Salt in salt water• CO2 in pop

SolventThe 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

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

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.

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) also 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 (page 277) 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? Which is stronger? 1 M acetic acid or

1M hydrochloric acid? Strength is determined by how well the

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

electrolytes.

Strong and Weak vs. Dilute and Concentrated Strong and weak refer to how well an

acid or base create ions in solution. If a large percentage of the molecules break up, then it is strong. If not, it is weak.

Dilute and Concentrated refer to the percentage of the solution that is made up of the solute.