Molecular View of
Reactions
in Aqueous Solutions
CHAPTER 5
Chemistry: The Molecular Nature of Matter, 6th edition
By Jesperson, Brady, & Hyslop
CHAPTER 5: Molecular View of Reactions
Learning Objectives
 Define a solution, solute, solvent
 Solubility Rules
 Concentration
 Dilution
 Solution Stoichiometry
 Writing chemical equations for reactions in
solutions
 Definition/basics of solution chemistry of Acids
& Bases
 Titrations
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Solutions
Definition
• For reaction to occur
– Reactants needs to come into physical contact
• Happens best in gas or liquid phase
– Movement occurs
Solution
• Homogeneous mixture
– Two or more components mix freely
– Molecules or ions completely intermingled
– Contains at least two substances
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Solutions
Examples of Solutions
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Solutions
Solutes and Solvents
Solvent
• Medium that dissolves solutes
– Component present in largest amount
– Can be gas, liquid, or solid
– Aqueous solution—water is solvent
Solute
• Substance dissolved in solvent
– Solution is named by solute
– Can be gas—CO2 in soda
– Liquid—ethylene glycol in antifreeze
– Solid—sugar in syrup
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Solutions
Electrolytes
In Water…
• Strong electrolytes produce ions and conduct an
electric current.
• Weak electrolytes produce a few ions.
• Nonelectrolytes do not produce ions.
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Solutions
Acids & Bases
• Arrhenius Theory
– Acids produce hydronium when dissolved in water
– Bases produce hydroxide when dissolved in water
• Bronsted-Lowry Theory
– Acids are proton (H+) donors.
– Bases are proton (H+) acceptors.
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Solutions
Acids & Bases
• Neutralization: metathesis reaction in which acid +
metal hydroxide or metal oxide forms water and salt
– NaOH(aq) + HCl(aq) →H2O(l) + NaCl(aq)
• Acid-base reaction: reaction of weak base and acid
transferring a H+ ion, driven by the formation of a weaker
acid.
– HCl(aq) + NH3(aq) →NH4Cl(aq)
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Solutions
Writing Solution Chemical Equations
• hydrated ions, with the symbol (aq), are written
separately
• Na2SO4(s) → 2Na+(aq) + SO42-(aq)
• you might encounter the equation as:
• Na2SO4(s) → 2Na+ + SO42– Accepted because only 2 states allow for dissociated
ions (plasma and aqueous). Aqueous is far more
common
– It is vague and not preferred
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Solutions
Writing Solution Chemical Equations
• Molecular equation:
– Balanced, shows states, all substances electrically
neutral
– AgNO3(aq) + KCl(aq) →AgCl(s) + KNO3(aq)
• Ionic equation:
– Balanced, shows states, shows strong electrolytes as
dissociated ions, net charges balance
– Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) →AgCl(s) + K+(aq) + NO3(aq)
• Net ionic equation:
– Balanced, shows states, eliminates spectator ions from
the ionic equation, net charges balance
– Ag+(aq) + Cl-(aq) →AgCl(s)
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Solutions
Criteria for Balancing Ionic &
Net Ionic Equations
Material Balance
• There must be the same number of atoms of
each kind on both sides of the arrow
Electrical Balance
• The net electrical charge on the left must equal
the net electrical charge on the right
• Charge does not have to be zero
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Solutions
Solubility
• saturated –no more solute can be dissolved at the
current temperature in the given amount of solvent
• solubility - the amount of solute that can dissolve in
the specified amount of solvent at a given temperature
(usually g solute/ 100 g solvent or moles solute/L
solution)
• unsaturated - contains less solute than the solubility
allows
• supersaturated- contains more solute than solubility
predicts
Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E
Brady & Senese 5th Ed
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Solutions
Solubility & Temperature
Solubility:
•Depends on temperature.
•Of most solids increases as
temperature increases.
•Of gases decreases as
temperature increases.
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Solutions
Solubility & Pressure
•Henry’s Law states
•The solubility of a gas in a
liquid is directly related to
the pressure of that gas
above the liquid.
•At higher pressures, more
gas molecules dissolve in
the liquid.
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Solutions
Concentration
• In solutions, solutes are dispersed in a larger volume
• Molarity expresses the relationship between the moles
of solute and the volume of the solution
• Molarity (M)=moles solute/L solution
– Hence, a 6.0M solution of HCl contains 6.0 mole HCl
in a liter of solution
moles of solute
mole
Molarity (M ) =
=
liters of solution volume
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Dilution
Solutions
• Can take solution of higher concentration and dilute it to a
lower concentration.
Small
Volume
Concentrated
Solution
Large
Volume
Dilute
Solution
Add solvent
• Amount of MOLES does NOT change
Remains the same
• moles of solute do not change, hence CstockVstock= CnewVnew
• C=concentration
• V=volume
Vdil  Mdil = Vconc  Mconc
Jesperson, Brady, Hyslop. Chemistry: The
Brady & Senese 5th Ed
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Solutions
Solubility Rules
A general idea as to whether a fair amount of solid will
dissolve is achieved using solubility rules
1. All compounds of the alkali metals (Group IA)
2. All salts containing NH4+, NO3−, ClO4−, ClO3−, and C2H3O2−
3. All chlorides, bromides, and iodides (salts containing Cl−,
Br−, or I−) except when combined with Ag+, Pb2+, and Hg22+
4. All sulfates (salts containing SO42−) except those of Pb2+,
Ca2+, Sr2+, Hg22+, and Ba2+
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Solutions
Solubility Rules
A general idea as to whether a fair amount of solid will
dissolve is achieved using solubility rules
5. All metal hydroxides (ionic compounds containing OH−)
and all metal oxides (ionic compounds containing O2−)
are insoluble except those of Group IA and Group IIA
• When metal oxides dissolve, they react with water to
form hydroxides. The oxide ion, O2−, does not exist
in water. For example, Na2O(s) +H2O(l)→ 2NaOH(aq)
6. All salts that contain PO43−, CO32−, SO32−, and S2− are
insoluble, except those of Group IA and NH4+.
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Solutions
Solution Stoichiometry
• Often work with solutions when conducting reactions
• How do we determine amounts needed to completely react
one compound?
• Like any other stoichiometry problem
• Now use volume and molarity to obtain moles of each
substance.
• Sometimes we need to know concentrations of ions
• Important for net ionic reaction stoichiometry
• Molar concentration of particular ion equals molar
concentration of salt multiplied by number of ions of that kind
in one formula unit of salt.
Brady & Senese 5th Ed
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Solutions
Titrations
• Is the controlled addition of one reactant (titrant) to a
known quantity of another reactant of unknown
concentration (analyte) until the reaction is complete
• Often, an indicator is used to signal the reaction
completion
• Endpoint: the volume of titrant required to complete
the reaction
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Solutions
Titrations
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