Irvington High School
Mr. Markic
AP Chemistry
Chapter 4-Reactions in Aqueous Solutions
A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount
Solution
Solvent
Solute
Soft drink (l)
H2O
Sugar, CO2
Air (g)
N2
O2, Ar, CH4
Soft Solder (s)
Pb
Sn
An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct
electricity.
A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct
electricity.
Conduct electricity in solution?
Cations (+) and Anions (-)
Strong Electrolyte – 100% dissociation
NaCl (s)
H2O
→
Na+ (aq) + Cl- (aq)
Weak Electrolyte – not completely dissociated
CH3COOH ↔
CH3COO- (aq) + H+ (aq)
Ionization of acetic acid
CH3COOH ↔ CH3COO- (aq) + H+ (aq)
↔
A reversible reaction. The reaction can occur in both directions
Acetic acid is a weak electrolyte because its ionization in water is incomplete.
Hydration is the process in which an ion is surrounded by water molecules arranged in a specific
manner.
δ-
δ+
Page 1 of 13
Irvington High School
Mr. Markic
AP Chemistry
Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
H2O
C6H12O6 (s) →
C6H12O6 (aq)
Review of Concepts
The diagrams here show three compounds AB2 (a), AC2 (b), and AD2 (c) dissolved in water. Which is
the strongest electrolyte and which is the weakest? (For simplicity, water molecules are not shown.)
Precipitation Reactions
A precipitate is an insoluble solid formed by a reaction in solution
precipitate

Pb(NO3)2 (aq) + 2NaI (aq)  PbI2 (s) + 2NaNO3 (aq)
molecular equation
Pb2+ + 2NO3- + 2Na+ + 2I-  PbI2 (s) + 2Na+ + 2NO3ionic equation
Pb2+ + 2I-  PbI2 (s)
net ionic equation
Na+ and NO3- are spectator ions
Sample Exercise
Classify the following ionic compounds as
soluble or insoluble:
(a) silver sulfate (Ag2SO4)
(b) calcium carbonate (CaCO3)
(c) sodium phosphate (Na3PO4).
(d) copper (II) sulfide (CuS).
(e) calcium hydroxide (Ca(OH)2).
(f) zinc nitrate (ZnNO3).
Page 2 of 13
Irvington High School
Mr. Markic
AP Chemistry
Writing Net Ionic Equations
1. Write the balanced molecular equation.
2. Write the ionic equation showing the strong electrolytes completely dissociated into cations
and anions.
3. Cancel the spectator ions on both sides of the ionic equation
4. Check that charges and number of atoms are balanced in the net ionic equation.
Sample Exercise
Predict what happens when a potassium phosphate (K3PO4) solution is mixed with a calcium
nitrate [Ca(NO3)2] solution. Write a net ionic equation for the reaction.
Practice Exercise
Predict the precipitate produced by mixing an Al(NO3)3 solution with a NaOH solution. Write the net
ionic equation for the reaction.
Review of Concepts
Which of the diagrams here accurately describes the
reaction between Ca(NO3)2(aq) and Na2CO3(aq)? For
simplicity, only the Ca2+ (yellow) and CO32- (blue) ions are
shown.
Properties of Acids
 Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid.
 Cause color changes in plant dyes.
 React with certain metals to produce hydrogen gas.
2HCl (aq) + Mg (s)  MgCl2 (aq) + H2 (g)

React with carbonates and bicarbonates to produce carbon dioxide gas
2HCl (aq) + CaCO3 (s) 

CaCl2 (aq) + CO2 (g) + H2O (l)
Aqueous acid solutions conduct electricity.
Page 3 of 13
Irvington High School
Mr. Markic
AP Chemistry
Properties of Bases
 Have a bitter taste.
 Feel slippery. Many soaps contain bases.
 Cause color changes in plant dyes.
 Aqueous base solutions conduct electricity.
Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water
A Brønsted acid is a proton donor
A Brønsted base is a proton acceptor
A Brønsted acid must contain at least one ionizable proton!
Monoprotic acids
HCl  H+ + ClStrong electrolyte, strong acid
HNO3  H+ + NO3Strong electrolyte, strong acid
CH3COOH  H+ + CH3COOWeak electrolyte, weak acid
Diprotic acids
H2SO4  H+ + HSO4HSO4-  H+ + SO42-
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Triprotic acids
H3PO4  H+ + H2PO4- Weak electrolyte, weak acid
H2PO4-  H+ + HPO42- Weak electrolyte, weak acid
HPO42-  H+ + PO43Weak electrolyte, weak acid
Review of Concepts
Which of the following diagrams best represents a weak acid? Which
represents a very weak acid? Which represents a strong acid? The proton exists in water as the
hydronium ion. All acids are monoprotic. (for simplicity, water molecules are not shown.)
Page 4 of 13
Irvington High School
Mr. Markic
AP Chemistry
Sample Exercise
Classify each of the following species in aqueous solution as a Brønsted acid or base:
(a) HBr
(b) NO3(c) HCO3-
Practice Exercise
Classify each of the following species as a Brønsted acid or base:
(a) SO42(b) HI
Neutralization Reaction
acid + base  salt + water
HCl (aq) + NaOH (aq)

H+ + Cl- + Na+ + OH- 
H+ + OH-
NaCl (aq) + H2O
Na+ + Cl- + H2O

H2O
Neutralization Reaction Involving a Weak Electrolyte
weak acid + base  salt + water
HCN (aq) + NaOH (aq)
HCN + Na+ + OHHCN + OH-



NaCN (aq) + H2O
Na+ + CN- + H2O
CN- + H2O
Practice Exercise
Write molecular, ionic, and net ionic equations for each of the following acid-base reactions:
(a) hydrobromic acid(aq) + barium hydroxide(aq)
(b) sulfuric acid(aq) + potassium hydroxide(aq)
Write a molecular equation, and ionic equation, and a net ionic equation for the reaction between
aqueous solutions of phosphoric acid and sodium hydroxide.
Page 5 of 13
Irvington High School
Mr. Markic
AP Chemistry
Neutralization Reaction Producing a Gas
acid + base 
salt + water + CO2
2HCl (aq) + Na2CO3 (aq)

2H+ + 2Cl- + 2Na+ + CO32- 
2H+ + CO32-

2NaCl (aq) + H2O +CO2
2Na+ + 2Cl- + H2O + CO2
H2O + CO2
Oxidation-Reduction Reactions (electron transfer reactions)
2Mg

O2 + 4e-
2Mg2+ + 4e
2O2-
2Mg + O2 + 4e- 
2Mg + O2


Cu2+ + 2e-
Zn2+ + 2e
Reduction half-reaction (gain e-)
2Mg2+ + 2O2- + 4e-
2MgO
Zn(s) + CuSO4(aq) 
Zn
Oxidation half-reaction (lose e-)
Cu
ZnSO4(aq) + Cu(s)
Zn is oxidized
Zn is the reducing agent
Cu2+ is reduced
Cu2+ is the oxidizing agent
Oxidation number
The charge the atom would have in a molecule (or an ionic compound) if electrons were completely
transferred.
1. Free elements (uncombined state) have an oxidation number of zero.
Na, Be, K, Pb, H2, O2, P4 = 0
2. In monatomic ions, the oxidation number is equal to the charge on the ion.
Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2
3. The oxidation number of oxygen is usually –2. In H2O2 and O22- it is –1.
4. The oxidation number of hydrogen is +1 except when it is bonded to metals in binary
compounds. In these cases, its oxidation number is –1.
5. Group IA metals are +1, IIA metals are +2 and fluorine is always –1.
6. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge
on the molecule or ion.
7. Oxidation numbers do not have to be integers. The oxidation number of oxygen in the
superoxide ion, O2-, is –½.
Page 6 of 13
Irvington High School
Mr. Markic
AP Chemistry
Sample Exercise
Assign oxidation numbers to all the elements in the following compounds and ion:
(a) Li2O
(c) Cr2O72-
(b) HNO3
(d) PF3
(e) MnO4-
Types of Oxidation-Reduction Reactions
1. Combination Reaction
A+B 
C
2Al + 3Br2 
2AlBr3
2. Decomposition Reaction
C
 A+B

2KClO3
2KCl + 3O2
3. Combustion Reaction
A + O2 
B
S + O2 
SO2
2Mg + O2

2MgO
4. Displacement Reaction
A + BC 
AC + B
Sr + 2H2O  Sr(OH)2 + H2
TiCl4 + 2Mg


Cl2 + 2KBr
Ti + 2MgCl2
2KCl + Br2
Hydrogen Displacement
Metal Displacement
Halogen Displacement
The Activity Series for Metals
i.
M + BC
Hydrogen Displacement Reaction

MC + B
M is metal
BC is acid or H2O
B is H2
Ca + 2H2O

Ca(OH)2 + H2
Pb + 2H2O

Pb(OH)2 + H2
Page 7 of 13
Irvington High School
Mr. Markic
AP Chemistry
The activity series for metals
The metals are arranged according to their ability to displace hydrogen from water or acids. Li
(Lithium) is the most reactive metal, and Au (gold) is the least reactive. Metal that acts as the
reducing agent lies above the metal that is reduced
•
•
•
ii.
Halogen Displacement
F2 > Cl2 > Br2 > I2
As we move down group 7A the power of the oxidizing agents decreases
Molecular fluorine is the most active nonmetal – it’s so reactive it even attacks water
Cl2 + 2KBr
•

2KCl + Br2
I2 + 2KBr

2KI + Br2
They are all strong oxidizing agents
Types of Oxidation-Reduction Reactions
1. Disproportionation Reaction
The same element is simultaneously oxidized and reduced.
reduced
Example:
0
Cl2 +
-1
+1
2OH-

ClO-
+
Cl- +
H2O
oxidized
Elements that are most likely to
undergo disproportionation
Sample Exercise
Classify the following redox reactions and indicate changes in the oxidation numbers of the elements:
(a) 2N2O(g)  2N2(g) + O2(g)
(b) 6Li(s) + N2(g)  2Li3N(s)
(c) Ni(s) + Pb(NO3)2(aq)  Pb(s) + Ni(NO3)2(aq)
(d) 2NO2(g) + H2O(l)  HNO2(aq) + HNO3(aq)
Practice Exercise
Identify the following redox reactions by type
(a) Fe + H2SO4  FeSO4 + H2
(c) 2CuCl  Cu + CuCl2
(b) S + 3F2  SF6
(d) 2Ag + PtCl2  2AgCl + Pt
Page 8 of 13
Irvington High School
Mr. Markic
AP Chemistry
Review of Concepts
Which of the following combination reactions is not a redox reaction?
(a) 2Mg(s) + O2(g)  2MgO(s)
(c) NH3 + HCl(g)  NH4Cl(s)
(b) H2(g) + F2(g)  2HF(g)
(d) 2Na(s) + S(s)  Na2S(s)
Solution Stoichiometry
The concentration of a solution is the amount of solute present in a given quantity of solvent or
solution.
moles of solute
M = molarity = liters of solution
(a) A known amount of a solid solute is transferred into the
volumetric flask; then water is added through a funnel
(b) The solid is slowly dissolved by gently swirling the flask
(c) After the solid has completely dissolved, more water is added to
bring the level of solution to the mark.
Knowing the volume of the solution and the amount of solute dissolved in it, we can calculate the
molarity of the prepared solution
This procedure does not require knowing the amount of water added, as long as the volume of
the final solution is known
Sample Exercise
How many grams of potassium dichromate (K2Cr2O7) are required to prepare a 250-mL solution
whose concentration is 2.16 M?
Practice Exercise
What is the molarity of an 85.0-mL ethanol (C2H5OH) solution containing 1.77 g of ethanol?
In a biochemical assay, a chemist needs to add 3.81 g of glucose to a reaction mixture. Calculate the
volume in milliliters of a 2.53 M glucose solution she should use for the addition.
What volume (in milliliters) of a 0.315 M NaOH solution contains 6.22 g of NaOH?
Page 9 of 13
Irvington High School
Mr. Markic
AP Chemistry
Dilution
Dilution is the procedure for preparing a less concentrated solution from a more concentrated
solution.
Dilution
→
Add solvent
Moles of solute
before dilution (i)
=
Moles of solute
after dilution (f)
MiVi
=
MfVf
The dilution of a more concentrated solution (a) to a less concentrated one (b) does not change the
total number of solute particles (18)
Sample Exercise
Describe how you would prepare 5.00 × 102 mL of a 1.75 M H2SO4 solution, starting with an 8.61 M
stock solution of H2SO4.
Practice Exercise
How would you prepare 2.00 x 102 mL of a 0.866 M NaOH solution, starting with a 5.07 M stock
solution?
Solution Stoichiometry
• The quantitative aspects of reactions in aqueous solution
• Two techniques for studying solution stoichiometry:
i.
Gravimetric analysis
ii.
Titration
• These are important tools of quantitative analysis, which is the determination of the amount
or concentration of a substance in a sample
i.
•
•
•
•
•
•
Gravimetric Analysis
Analytical technique based on the measurement of mass
Involves formation, isolation, and mass determination of a precipitate
Applied to ionic compounds
Highly accurate technique – because the mass of a sample can be measured accurately
Reactions must go to completion (totally insoluble in water)
Does not establish the whole identity of the unknown, but the percent by mass helps identify
the unknown
Page 10 of 13
Irvington High School
Mr. Markic
AP Chemistry
Gravimetric Analysis
1. Dissolve unknown substance in water
2. React unknown with known substance to form a precipitate
3. Filter and dry precipitate
4. Weigh precipitate
5. Use chemical formula and mass of precipitate to determine amount of unknown ion
Sample Exercise
A 0.5662-g sample of an ionic compound containing chloride ions and an unknown metal is dissolved
in water and treated with an excess of AgNO3. If 1.0882 g of AgCl precipitate forms, what is the
percent by mass of Cl in the original compound?
A sample of 0.3220 g of an ionic compound containing the bromide ion (Br-) is dissolved in water and
treated with an excess of AgNO3. If the mass of the AgBr precipitate that forms is 0.6964 g, what is
the percent by mass of Br in the original compound?
Review of Concepts
Calculate the mass of AgBr formed if a solution containing 6.00 g of KBr is treated with an excess of
AgNO3
Titrations
In a titration a solution of accurately known concentration (standard solution) is added gradually
added to another solution of unknown concentration until the
chemical reaction between the two solutions is complete.
Equivalence point – the point at which the reaction is complete
(neutral)
Indicator – substance that changes color at (or near) the
equivalence point (phenolphthalein)
Sample Exercise
In a titration experiment, a student finds that 23.48 mL of a NaOH solution are needed to neutralize
0.5468 g of KHP (Potassium Hydrogen Phthalate (monoprotic acid) = 204.4 g/mol). What is the
concentration (in molarity) of the NaOH solution?
Page 11 of 13
Irvington High School
Mr. Markic
AP Chemistry
How many grams of KHP (Potassium Hydrogen Phthalate (monoprotic acid) = 204.4 g/mol) are
needed to neutralize 18.64 mL of a 0.1004 M NaOH solution?
Practice Exercise
How many milliliters (mL) of a 0.610 M NaOH solution are needed to neutralize 20.0 mL of a 0.245 M
H2SO4 solution?
How many milliliters of a 1.28 M H2SO4 solution are needed to neutralize 60.2 mL of a 0.42 M KOH
solution?
Review of Concepts
A NaOH solution is initially mixed with an acid solution shown in (a). Which of the diagrams in (b)-(d)
corresponds to one of the following acids: HCl, H2SO4, H3PO4? Color codes: Blue spheres (OHions); red spheres (acid molecules); green spheres (anions of the acids). Assume all the acid-base
neutralization reactions go to completion.
Sample Exercise
A 16.42-mL volume of 0.1327 M KMnO4 solution is needed to oxidize 25.00 mL of a FeSO4 solution in
an acidic medium. What is the concentration of the FeSO4 solution in molarity? The net ionic
equation is:
5Fe2+ + MnO4- + 8H+  Mn2+ + 5Fe3+ + 4H2O
How many milliliters of a 0.206 M HI solution are needed to reduce 22.5 mL of a 0.374 M KMnO4
solution according to the following equation:
10 HI + 2KMnO4 + 3H2SO4  5I2 + 2MnSO4 + K2SO4 + 8H2O
Page 12 of 13
Irvington High School
Mr. Markic
AP Chemistry
Big Idea 3: Changes in Matter involve the rearrangement and/or reorganization of atoms and/or the transfer of
elections
Duration: Early October
Textbook Chapter: 4
Enduring Understanding
Essential Knowledge
3.A: Chemical changes are represented by a balanced 3.A.1: A chemical change may be represented by a
chemical equation that identifies the ratios with
molecular, ionic, or net ionic equation.
which reactants react and products form.
3.A.2: Quantitative information can be derived from
stoichiometric calculations that utilize the mole ratios
from the balanced chemical equations. The role of
stoichiometry in real-world applications is important to
note, so that it does not
seem to be simply an exercise done only by chemists.
3.B: Chemical reactions can be classified by
3.B.1: Synthesis reactions are those in which atoms and/or
considering what the reactants are, what the
molecules combine to form a new compound.
products are, or how they change from one into the
Decomposition is the reverse of synthesis, a process
other. Classes of chemical reactions include synthesis, whereby molecules are
decomposition, acid-base, and oxidation-reduction
decomposed, often by the use of heat.
reactions.
3.B.2: In a neutralization reaction, protons are transferred
from an acid to a base.
3.B.3: In oxidation-reduction (redox) reactions, there is a
net transfer of electrons. The species that loses electrons
is oxidized, and the species that gains electrons is
reduced.
3.C: Chemical and physical transformations may be
3.C.1: Production of heat or light, formation of a gas, and
observed in several ways and typically involve a
formation of a precipitate and/or a color change are
change in energy.
possible evidences that a chemical change has occurred.
Learning Objectives
1.19 The student can design, and/or interpret data from, an experiment that uses gravimetric analysis to
determine the concentration of an analyte in a solution.
1.20 The student can design, and/or interpret data from, an experiment that uses titration to determine the
concentration of an analyte in a solution.
2.1 Students can predict properties of substances based on their chemical formulas, and provide explanations of
their properties based on particle views.
3.1 Students can translate among macroscopic observations of change, chemical equations, and particle views.
3.2 The student can translate an observed chemical change into a balanced chemical equation and justify the
choice of equation type (molecular, ionic, or net ionic) in terms of utility for the given circumstances.
3.7 The student is able to identify compounds as Bronsted-Lowry acids, bases, and/or conjugate acid-base pairs,
using proton-transfer reactions to justify the identification.
3.8 The student is able to identify redox reactions and justify the identification in terms of electron transfer.
3.9 The student is able to design and/or interpret the results of an experiment involving a redox titration.
3.10 The student is able to evaluate the classification of a process as a physical change, chemical change, or
ambiguous change based on both macroscopic observations and the distinction between rearrangement of
covalent interactions and noncovalent interactions.
5.10 The student can support the claim about whether a process is a chemical or physical change (or may be
classified as both) based on whether the process involves changes in intramolecular versus intermolecular
interactions.
Page 13 of 13