AP Chemistry
th
Zumdahl Notes, 9 ed.
A Brief Collection of notes, Chapter 4
Feel free to open these files and annotate as you feel the need…this is
for your success.
Types of Chemical Rxns. & Solution Stoich.
• Water, the common solvent
• Sometimes referred to as the universal solvent, aqueous solutions are where much
chemistry occurs, as water allows the ionic compounds to be dissociated into ions
which can react with other ions to form new compounds (insoluble to be seen as
products)
• How does this occur? We need to recall/realize that water is a polar molecule, polar
enough to dissolve many compounds This process is called hydration, where the salt
comes apart in the water, forming the aqueous solution containing the ions which
previously were the salt
• Water can also dissolve many nonionic compounds, but most of these have some
source of polarity in their own molecules, like simple alcohols, so that they will
interact with water’s polar molecule well. Substances that are much more nonpolar
will not dissolve well…think fats, which are long chain hydrocarbons with much less
polar nature. Hydrocarbons in general are immiscible (incapable of attaining a
homogeneous state with water)
• Consider the rule: “like dissolves like”
• Remember: solute dissolve in solvent
Types of Chemical Rxns. & Solution Stoich.
• Nature of Aqueous Solutions: strong/weak electrolytes
• Electrical conductivity: the ability to conduct an electrical current
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What is needed? Lots of ions to allow for the passage of charge
Weak electrolytes: dissociate only partially…small current flow
Strong electrolytes: dissociate largely/completely…large current flow
Nonelectrolytes: virtually no dissociation…no current flow
Idea of conductivity being due to the presence of ions first identified by Svante
Arrhenius. He established the idea of how current flow being directly proportional to the
quantity of ions present in the solution (yes, this really is a big deal!) 
This allowed Arrhenius to further propose that an acid produces H+ when dissolved into
water…these are also strong electrolytes if they dissociate largely…hence, strong acids
This then directs us to consider strong bases, those that dissociate and produce OH- ions
Weak electrolytes, thus, are those which produce either ions, H+ or OH-, but not
completely…they dissociate/ionize to a limited extent
Nonelectrolytes…the molecule stays intact when it dissolves in water
Types of Chemical Rxns. & Solution Stoich.
• Composition of Solutions: how to describe what we have
• Molarity (M): moles solute/liters solution
• As previously discussed, when you work with this in problems, it is useful to virtually
automatically insert this conversion so you know where you have to go in your equation
• 1.0M means one mole solute per one liter solution
• Calculations
• Simple deal, just like stoichiometry in general: you need to get to moles, volume in liters
to get anywhere in these calculations…may take 0, 1, 2, possibly more steps
• If calculating ions, realize that paying attention to the subscripts is crucial for accuracy
• Dilutions
• Realization: moles before and after must remain the same
• M1v1=M2v2
Realization 2: molarity x volume = moles! Yeah, we are there!
Types of Chemical Rxns. & Solution Stoich.
• Types of chemical reactions that can occur in solutions:
• Precipitation reactions
• Acid/base reactions
• Oxidation/reduction reactions
Types of Chemical Rxns. & Solution Stoich.
• Precipitation Reactions: soluble solution + soluble solution  soluble
solution and precipitate from new compound formed
• Consideration…solubility rules…oh, yeah, these tell you what the new
compound could be. Useful? VERY! Note small table on 156…might
want to remember a lot of this
• Reality check: be thoughtful about how much of a solute you are trying to
dissolve…it is possible to go past the solubility of a given material
Types of Chemical Rxns. & Solution Stoich.
• Describing Reactions in Solution
• Yes, Virginia, there is a Santa Claus…we do have methods for describing what
is happening in solution reactions
• Formula equation: K2CrO4(aq) + Ba(NO3)2(aq) BaCrO4(s) + 2KNO3(aq)
• Complete/total ionic equation:
2K+(aq) + CrO42-(aq) + Ba2+(aq) + 2NO3-(aq)  BaCrO4(s) + 2K+(aq) + 2NO3-(aq)
• Net ionic equation (what really happens): Ba2+(aq) + CrO42-(aq)  BaCrO4(s)
• Typically you will have problems where you will have to start with the formula equation
and work your way through these and, likely, then start some other calculations about
product or reactant amounts…yep.
Types of Chemical Rxns. & Solution Stoich.
• Stoichiometry of Precipitation Reactions
• First thought: need to figure out which reaction may be occurring
• Solubility rules, after total ionic equation…what can form?
• Realize that moles and volumes are critical…may be past solubility point of some
materials, even if they are “normally” totally soluble…think solubility curves (see pg. 520,
figure 11.6)
• Don’t forget to pay attention if things like percent yield are included…be awful to assume
100% when they tell you 82%....
Types of Chemical Rxns. & Solution Stoich.
• Acid/base reactions
• Arrhenius definition: acids: H+ donor, bases: OH- donor
• Bronsted-Lowry: acids: proton (H+) donor, bases: proton (H+) acceptor
• We must realize that, in a given reaction, if H+ and OH- are present, it is likely that one
product formed will be H-OH, water…this will be the net ionic equation, especially if the
cation and anion formed are of a soluble compound.
• Idea to know: if a hydroxide source reacts with a weak acid, it is assumed that the
reaction will go completely, as the hydroxide is such a strong base, it will drive it forward.
• As with other stoich: start with formula equation, move to total ionic, then net ionic
equations, so that you can know all of what is present; calculate moles of all ions
present, determine limiting reactants as you can, calculate moles of products or
reactants, as needed; finish any last output conversions, again, as needed.
Types of Chemical Rxns. & Solution Stoich.
• Acid-base titrations
• This is a volumetric analysis technique for determining the concentration of a
certain substance (analyte) by measuring it against a known concentration of
another substance (titrant) (terms from Zumdahl, pg. 166).
• Watch these to understand titrations…yes, you will be doing this sometime
later in this course
• https://www.youtube.com/watch?v=8UiuE7Xx5l8
• https://www.youtube.com/watch?v=sFpFCPTDv2w
• The equivalence point/stoichiometric point is usually shown by an indicator
undergoing a color change at/near the endpoint of the titration (clearly
shown in the videos). Frequently these are neutralizations….
• Completion of problems revolves around what is asked for…it all depends on
the form of the answer required what steps you will need to do to get there.
Types of Chemical Rxns. & Solution Stoich.
• Oxidation/reduction reactions
• Reality check: many reactions involve the rearrangement of the electrons
present within a system; most biological chemical reactions involve
these…think of all the cycles for the storage and release of energy!
• Must be familiar with oxidation states/numbers: the arbitrary assignment of
electrons to atoms within a compound; I am including the table from pg. 171
on the next slide to ensure that you are comfortable with deducing these
• BIG REALITY CHECK: remember…the sum of oxidation states, like charge, must
total zero for a compound
Types of Chemical Rxns. & Solution Stoich.
• Table 4.2: rules for assigning oxidation states
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An atom in an element is zero, always; examples: Na(s), O2(g), Hg(l)
A monoatomic ion is the same as its charge; Na+, Cl-, Ca2+
Fluorine is -1 in its compounds, always; HF, PF3
Oxygen is usually -2 except for peroxides (O2-2); H2O, CO2, CaO
Hydrogen is +1 in its covalent compounds; H2O, HCl, NH3
• Convention is that, for oxidation states are written as +/-n, and that actual
charges are shown as n+/-
Types of Chemical Rxns. & Solution Stoich.
• Other rules for oxidation numbers:
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Hydrogen is -1 if acting as anion, in a metal hydride
Ia metals: +1
IIa metals: +2
VIIa elements: typically -1
The sum of the oxidation numbers of a polyatomic ion equals the ion’s charge.
For example, the sulfur’s ox. # in SO42- is +6, as final sum = -2.
• As a periodic trend, lower left tends to be positive, while upper right tends to
be less so
Types of Chemical Rxns. & Solution Stoich.
• Characteristics of Red/ox (oxidation-reduction) reactions
• Transfer of electrons (by definition)
• Mnemonics
• OIL RIG (oxidation is loss, reduction is gain)
• LEO says GER (loss of electrons is oxidation, gain of electrons is reduction)
• Oxidation: if loss of electrons, means species oxidized is losing more
electrons, so has an increase in oxidation #
• Reduction: a gain in electrons, so a reduction in oxidation #
• Either of these may result in a change of sign for the oxidation number of the given
element involved
Types of Chemical Rxns. & Solution Stoich.
• Balancing Redox reactions
• Since the total must balance, electrons gained by one species involved must
equal electrons lost by another species, we can find ourselves working to
balance this in a way very similar to balancing an equation
• Procedure, a la Zumdahl (pg. 176)
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Write unbalanced equation
Determine oxidation states of all atoms in reactants and products
How electrons gained and lost with “tie lines” between before/after
Use coefficients to equalize, like conventional balancing
Complete as needed
Add appropriate states (solid, liquid, gas)