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: Dissociation Dispersion 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 water Physical 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 Concentrated A large amount of solute dissolved in a solvent Dilute A 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: Sour taste (never taste a chemical) All contain hydrogen Also called “proton donors” React with active metals to produce hydrogen gas. Zn + 2HCl ZnCl2 + H2

Indicators Chemicals used to identify acids and bases by changing color. ACIDS: Litmus paper (blue to red) Phenolphthalein (colorless) Methyl Orange (orange to red) 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.