AP Chemistry
Chapter 4
Solution Stoichiometry
I.
II.
III.
IV.
V.
VI.
The electrons in the covalent bonds of water aren’t shared evenly
a. oxygen is more electronegative.
b. They spend more time close to O than to H.
c. This uneven distribution of charge makes water polar.
i. This makes water a very good solvent.
d. The positive end (H) attracts negative ions or the negative end of another polar
molecule.
e. The negative end of water (O) attracts the positive ions or the positive ends of another
polar molecule.
When water surrounds an ionic crystal, the H end attracts the anion and the O end attracts
the cation. This process is called hydration
a. Hydration causes salts to dissolve.
b. Water also dissolves polar covalent substances such as C2H5OH.
c. Water doesn’t dissolve nonpolar covalent substances because there is not enough
attraction between water and the nonpolar covalent substance.
A solution is a homogenous mixture.
a. IN a solution, a solute dissolves in the solvent.
b. If the solute ionizes in the solution, electricity can be conducted and the solute is said to
be an electrolyte.
c. If the solute ionizes 100% or nearly 100%, it is called a strong electrolyte.
i. Soluble salts
ii. Strong acids (HCl , HNO3, H2SO4)
iii. Strong bases – completely ionizez
1. Contains OH
2. Bitter taste and slippery feel
3. NaOH , KOH
d. Lesser ionization occurs with weak electrolytes.
i. Only ionizes slightly (weak acids and bases)
ii. HC2H3O2  H+ + C2H3O2Molarity (M) = moles of solute / liters of solution
Dilution M1V1 = M2V2
Types of Reactions
a. SEE FLOWCHART!!!
b. It helps, yo!
c. But in case you are one sadistic person… here are the rules…
d. Decomposition Rxns
i. A compound may break down to produce two elements
ii. A compound may break down to produce an element and a compound
iii. A compound may break down to produce two compounds
iv. Metallic carbonates break down to yield metallic oxides and carbon dioxide
v. Metallic chlorates break down to yield metallic chlorides and oxygen
vi. Metallic sulfites break down to yield metallic oxides and sulfur dioxide
vii. Hydrogen peroxide decomposes into water and oxygen
viii. Sulfurous acid decomposes into water and sulfur dioxide
ix. Carbonic acid decomposes into water and carbon dioxide
x. Hydrated salts decompose into the salt and water.
e. Addition Rxns (aka synthesis, combination, or composition)
i. A Group IA or IIA metal may combine with a nonmetal to make a salt
ii. Two nonmetals may combine to form a molecular compound
iii. Two compounds combine to form a single product
iv. A metallic oxide plus carbon dioxide yields a metallic carbonate
v. A metallic oxide plus sulfur dioxide yields a metallic sulfite
vi. A metallic oxide plus water yields a metallic hydroxide
vii. A nonmetallic oxide plus water yields an acid
f. Double Replacement (metathesis)
i. All double replacement rxns must have a “driving force” that removes a pair of
ions from solution.
ii. Formations of a precipitate
1. A precipitate is an insoluble substance formed by the rxn of two
aqueous substances.
2. Two ions bond together so strongly that water cannot pull them apart
iii. Simple Rules for Solubility
1. Most nitrate salts are soluble
2. Most alkali salts and NH4+ are soluble.
iv. Formation of a gas
1. Gases may form directly in a double replacement rxn or can form from
the decomposition of a product such as H2CO3 or H2SO3.
a. Don’t leave carbonic or sulfurous acids, or ammonium
hydroxide as products of double replacement rxn—
DECOMPOSE THEM!
v. Formation of a molecular substance
1. When a molecular substance such as water or acetic acid is formed, ions
are removed from solution and the rxn “works”.
g. Single replacement
i. In a single replacement rxn, one element displaces another in a compound. One
element is oxidized and another is reduced.
1. A + BC  AC + B
VII.
VIII.
IX.
X.
XI.
XII.
XIII.
ii. Active nonmetals replace less active nonmetals from their compounds in
aqueous solution.
1. Each halogen will displace heavier halogens from their binary salts.
Activity Series of Nonmetals
a. Decreasing Activity  F, Cl, Br, I
b. Active metals replace less active metals or hydrogen from their compounds in aqueous
solution.
Activity Series of Metals
a. Decreasing Activity  Li, K, Ba, Ca, Na, Mg, Al, Zn, Fe, Cd, Ni, Sn, Pb, H, Cu, Hg, Ag, Au
b. Metals from Li to Na will replace H from water and acids; metals from Mg to Pb will
replace H from acids only.
Combustion Reactions
a. In the presence of excess oxygen, most hydrocarbons and alcohols can undergo
complete combustion rxns to form carbon dioxide and water.
Analysis terms
a. Selective precipitation – process by which ions are caused to ppt one by one in
sequence to separate mixtures of ions.
b. Qualitative analysis – process of separating and identifying ions
c. Quantitative analysis – determines how much of a component is present
d. Gravimetric analysis – quantitative procedure where a ppt containing a substances is
formed, filtered, dried, and weighed.
Acid-Base Rxns (type of Double Replacement)
a. Bronsted-Lowry
i. Acid – proton donor
ii. Base – proton acceptor
b. When a strong acid and a strong base react, the net ionic rxn is:
i. H+ + OH-  H2O
c. When a strong acid reacts with a weak base or a weak acid reacts with a strong base,
the rxn is complete (the weak substance ionizes completely.)
d. Neutralization Rxn – when just enough base is added to react exactly with the acid in a
solution, the acid is said to be “neutralized”
Volumetric Analysis (titration)
a. Titration – process in which a solution of known concentration (standard solution) is
added to analyze another solution.
b. Titrant – solution of known concentration (in buret)
c. Equivalence point (stoichiometric point) – point where just enough titrant has been
added to react with the substance being analyzed
d. Indicator – chemical which changes color at or near the equivalence point
e. End point – point at which the indicator changes color
Net Ionic Equations
a. Net ionic equations show only the species actually involved in the rxn.
XIV.
XV.
b. As you first learn to write net ionic equations, you will write three different eq. for each
rxn
c. Steps in writing net ionic equations:
i. Write the complete molecular equation
ii. Write the complete ionic equation
1. To do this, you must ionize everything that is soluble and ionized in
solution.
2. Everything else is left together. Do not ionize solids, gases or weak
electrolytes such as acetic acid.
iii. Write the net ionic equation
1. To do this, cancel out all ions that are not participating in the rxn
(spectator ions) and rewrite the equation
Oxidation-Reduction Reactions
a. Redox Rxns – reaction in which one or more electrons are transferred.
i. All single replacement and combustion, many synthesis, and many
decomposition reactions are redox.
ii. Many redox reactions are more complex and can’t be balanced by the
inspection method
b. Electronegativity – attracted for shared electrons
i. MOST ELECTRONEGATIVE ELEMENTS
ii. F > O > N > Cl
iii. “Phone Call”
c. Oxidation State (or Oxidation Numbers) Rules
i. Oxidation state of an atom in an element = 0
ii. Oxidation state of monatomic element = charge
iii. Oxygen = -2 in covalent compounds (except peroxides where it = -1)
iv. H = +1 in covalent compounds
v. Fluoride = -1 in compounds
vi. Sum of oxidation states = 0 in compounds
1. Sum of oxidation states = charge of ions
d. Oxidation – loss of electrons or increase in oxidation number
e. Reduction – gain of electrons or decrease in oxidation number
i. OIL – Oxidation Is Loss
ii. RIG – Reduction Is Gain
iii. Oxidizing agent – electron acceptor; substance that is reduced
iv. Reducing agent – electron donor; substance that is oxidized
Balancing Redox Rxns by the Half-Rxn Method
a. Write skeleton half-rxns
b. Balance all elements other than O and H
c. Balance O by adding H2O
d. Balance H by adding H+
e. Balance charge by adding e- to the more positive side.
f.
g.
h.
i.
j.
Make the # of e- lost = # of e- gained by multiplying each half-rxn by a factor.
Add half-rxns together
Cancel out anything that is the same on both sides.
If the rxn occurs in basic solution, add an equal number of hydroxide ions to both sides
to cancel out the hydrogen ions. Make water on the side with the hydrogen ions.
Cancel water if necessary.
Check to see that charge and mass are both balanced.