CHAPTER 4

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CHAPTER 4
AP CHEMISTRY
PRECIPITATION
PROBLEMS
Water
Highly polar
Ionic and polar compounds are attracted to the positive
and/or negative ends of the water molecule. This is
called HYDRATION (a hydration reaction is something
different)
When a precipitate is formed there is a zero net charge
Solubility rules (handout)
What happens when a ionic compound dissolves in water?
They break up into their ion form
What are spectator ions?
Ions that do not participate in the reaction
You must show that atoms and charges are balanced
ELECTROYTES
 Solute - substance
 Solvent - water, what you put solute in
 Electrolytes- conduct electricity
 Strong - strong acids and bases, soluble salts
 Weak - weak acids and bases, insoluble or slightly
soluble salts
 Nonelectroytes - molecules, nonpolar covalent
compounds
 ARRHENIUS
 Ions are responsible for conducting electricity
 Down played convictions to get PhD then crusaded
to get theory accepted
 Received Nobel prize 1903
OXIDATION-REDUCTION
REACTIONS
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An oxidation-reduction reaction involves transfer of electrons
Addition of O2 or H2 often occur
LEO goes GER
Oxidized or oxidation
 Species that lose electrons
 oxidation number goes up
 Reduced or reduction
 Species that gain electrons or oxidation number reduced
 Oxidizing agent
 What causes oxidation
 Reducing agent
 What causes reduction
OXIDATION NUMBER
RULES
 Elements found in nature is zero
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 Cu, O2
Monoatomic ions same as charge
 Cl-, Mg2+
Fluorine always 1Oxygen 2 Except with fluorine 2+
 Peroxide 1-, H2O2
 Superoxide ½ -, KO2
Hydrogen 1+
 With group one elements then a hyride 1Sum of oxidation numbers of a neutral compound is zero
The most electronegative element number is the same as the
ion charge
Sum of oxidation numbers of a polyatomic ion is same as its
charge
REDOX
 The concept of oxidation numbers explain oxidation and
reduction
 Oxidation: increase in oxidation number (lose electrons)
 Reduction: decreases in oxidation number (gain electrons)
 Balancing redox equations
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The half-equation method
Split the equation into two half-reactions
One for reduction and the other for oxidation
Balance one of the half-reactions; balance atom other than O or H
first, next use water to balance oxygen, then add hydrogen ions to
balance the hydrogen, add electrons to balance charge
 Balance other half-reaction
 Combine the two in such away as to eliminate all the electrons
MOLARITTY
 Number of moles of solute per liter of
solution
 M = number of mol/L
 Symbol [ ] means molar concentration
 Moles of solute after dilution = moles of
solute before dilution
 M1V1 = M2V2
TITRATION
 A volumetric analysis involving titration,
where a measured volume of a known
concentration of an acid or base is required
to find the exact concentration (the volume
must be known) of an unknown base or acid
 Equivalent point
 Where exact stoichometry amounts of
each reactant are present. (same number
of H+ and OH- ) NO EXCESSES
 End point
 Where the indicator changes color.
Immediately stop adding titrate.
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