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CHEM 115: EXAM 2
Solution |
Homogenous substance
-may be gas, liquid, or solid |
Solvent
|
component present in the greatest quantity in a solution |
Solute |
components of a solution in lesser quantities than solvent |
Molarity (molar concentration) |
Number of moles of solute divided by liters of solution |
Dilution
|
creating a less concentrated solution by adding more solvent |
M of solute= |
Molarity x Volume
(Mi x Vi= Mf x Vf) |
Water |
-polar molecule with a dipole
-bent molecular shape
-uneven distribution of electrons |
Electron distribution in H2 and H2O |
H2: symmetrical
H2O: asymmetrical, each bond is polar, entire molecule is polar |
Strong electrolytes
|
dissociate almost completely into ions in water. Ions are hydrated (surrounded by water molecules). Charge carriers in solution lead to good conductivity.
(soluble ionic compounds, strong acids, strong bases, most molecular hydrogen halides)
|
Nonelectrolyte |
Does not dissociate into ions in a water solution. Solution does not conduct electricity.
(most molecular compounds)
|
Weak Electrolytes
|
dissociates only partially to ions in solution of water. Only partial conductivity of electrical currents.
(create weak acids + bases such as HF, NH3)
|
Ways to write molecular equations
|
All reactants and products written as chemical formulas
|
Ways to write Ionic equations
|
compounds that dissociate are written in ionic form. spectator ions appear on both sides of the equation
|
Ways to write a net ionic equation |
eliminate spectator ions; shows net reaction
|
Net Ionic Equation
|
Must be balanced both by atoms and charge. Focuses only on net chemical change. Emphasizes similarities in chemistry. |
Types of reactions in solutions
|
precipitation
acid-base
oxidation-reduction |
Precipitation reactions
|
soluble reactants yield an insoluble product. also known as double displacement or metathesis
|
Acid-base reactions
|
acid reacts with base to afford water and salt. also called a neutralization. can be viewed as a proton (H+) transfer reaction.
|
Oxidation-reduction reactions
|
involves transfer of electrons between reaction partners. charges on atoms in reactants can change. O atoms can appear to be transferred. also called redox. reactions can be run so electrons flow in external wire as electricity. |
Solubility rules (predict precipitation reactions)
|
-All NH4+ & alkali metal compounds (Li+,Na+,K+,Rb+,Cs+) are soluble
-all NO3-,C2H3O2-,HCO3-,ClO4- compounds soluble
-all Cl-,Br-, I- compounds are soluble, except for Ag+, Hg22+, Pb2+
-All SO42- compounds are soluble except for Ba2+, Sr2+, Pb2+, Ag+, and Ca2+
-Most O2-, OH0, CO32-, and S2- are insoluble, except Na+, K+, NH4+. Ba(OH)2 is partially soluble
|
Balanced Chemical Equations
|
-total number of atoms unchanged
-net charge unchanged
-only adjust coefficients
|
Combustion reaction
|
reactants: Compound + O2
Products: CO2+H2O+ other element oxides
|
Precipitation reaction
|
reactants: two or more ionic compounds
products: pairwise exchange of ions
|
general procedure for stoichiometry problems
|
mass known/MW=mol known
mol unknown x MW= mass unknown
|
Limiting reagents
|
-reactions eventually consume all of one reactant and stop
-other reactants are in excess and called excess reactants
|
Percent yield
|
(actual yield/theoretical yield) x 100
|
Concentration
|
-number of grams of solute per 100 g of solution
|
Solubility |
-number of grams of solute that can dissolve in 100g of solvent at a given temperature
-often increases with temp
-supersaturated solutions are unstable and often result in the formation of a precipitate
|
Molarity |
molar concentration (M)= number of mol solute/number of L solution
|
Dilutions |
*moles of solute are constant
Moles of solute= molarity x volume (Mi x Vi = Mf x Vf)
|
Solubility Rules Predict Precipitation Reactions
|
1. identify all cations and anions present
2. apply solubility rules to each possible pair
3. any insoluble pair will precipitate
|
Acids |
react with water to produce H+ (aq)
generally molecular compounds that ionize |
Bases |
substances that react with water to produce OH- (aq)
tend to be ionic compounds
|
Titration |
quantitative, volumetric technique used to determine concentration of 'unknown' solution.
Mb x Vb = Ma x Va
|
Oxidation-reduction reaction
|
oxidation-
|
OILRIG |
Oxidation
Involves
Loss of electrons
Reduction
Involves
Gain of electrons |