Chapter 4: Solution Chemistry: The Hydrosphere
(Topics to Review)
EVIDENCE OF A CHEMICAL REACTION
a) A gas is produced.
b) A precipitate forms.
c) Heat is released/absorbed
Types of Chemical Reactions
• Precipitation Reactions
• Acid-Base Neutralization Reaction
• Oxidation-Reduction (Redox) Reactions
– Also classified as combination, decomposition, combustion, and single-replacement
reactions
4.7 PRECIPITATION REACTIONS
Solubility Rules: Indicate if an ionic compound is soluble or insoluble in water.
– Keep in mind that these are just general guidelines, and in reality, some ionic compounds
may only be slightly soluble, and solubility may depend on temperature.
Solubility Rules for Ionic Compounds in Water
Soluble if the ionic compound contains:
1. Li+, Na+, K+, NH4+ (ALWAYS!)
2. C2H3O2–, NO3–, ClO3–, ClO4–
3. Halide ions (X–): Cl–, Br–, or I–, but AgX, PbX2,
HgX, and Hg2X2 are insoluble
4. sulfate ion (SO42-), but CaSO4, SrSO4, BaSO4,
Ag2SO4, `and PbSO4 are insoluble.
Insoluble if the ionic compound contains:
5. carbonate ion, CO326. chromate ion, CrO427. phosphate ion, PO438. sulfide ion (S2–), but CaS, SrS, and
BaS are all soluble.
9. hydroxide ion (OH–), but Ca(OH)2,
Sr(OH)2, and Ba(OH)2 are soluble.
soluble = compound dissolves in water → exists as individual ions in solution
→ physical state is aqueous, (aq)
insoluble = compound does not dissolve in water but remains a solid
→ physical state is shown as solid, (s)
CHEM 161: Chapter 4 Review Notes v0916 p. 1 of 10 Ex. 1 Use the Solubility Rules and identify the ionic compounds are soluble or insoluble by
indicating the physical state of each compound.
a. NaCl
d. LiOH
g. Mg(OH)2
j.
Ag3PO4
b. MgS
e. CaS
h. SrSO4
k. BaCO3
c. K3PO4
f. Li2CrO4
i. Na2CO3
l. (NH4)2CrO4
Ex. 2 Use your answers from Ex. 1 to draw each soluble compound as individual ions and each
insoluble compound as a solid at the bottom of the beaker:
NaCl
MgS
K3PO4
Ag3PO4
(NH4)2CrO4
In a precipitation reaction, two solutions react to form a precipitate (an insoluble solid):
AX(aq) + BZ(aq)
→ AZ(s) + BX(aq)
precipitate
To balance and complete the following reactions:
1. Exchange the anions, writing the formulas for the
products based on the charges of the ions!
2. Use the Solubility Rules to determine if each product is
soluble or insoluble.
– If at least one product is insoluble, a precipitate
reaction has occurred, so write the formulas for
both products, indicating the precipitate as(s), then
balance the equation.
– If both products are soluble—both(aq)—then write
NR=no reaction.
3. Keep in mind that the charges on ions do NOT
change in precipitation reactions.
CHEM 161: Chapter 4 Review Notes v0916 p. 2 of 10 For metals that can form more than one charge, use the charge on the metal ion from the
reactant side of the equation.
Ex 1.
MgSO4(aq)
+
NaOH(aq)
→
+
Ex 2.
K2CO3(aq)
+
→
AlCl3(aq)
+
Ex 3.
SrBr2(aq)
+
→
Zn(NO3)2(aq)
+
→
→
→
CHEM 161: Chapter 4 Review Notes v0916 p. 3 of 10 UNSATURATED, SATURATED, AND SUPERSATURATED SOLUTIONS
If a solid is soluble in a solvent, more solid dissolves in the solvent at higher temperatures.
unsaturated:
saturated:
contains less than the maximum amount of solute that a solvent can hold at a
specific temperature
contains the maximum amount of solute that a solvent can hold at a specific
temperature
supersaturated:
contains more than the maximum amount of solute that a solvent should
be able to hold at specific temperature
A supersaturated NaC2H3O2 solution recrystallizing after addition of more solute:
https://www.youtube.com/watch?v=BLq5NibwV5g
How can a solution hold more solute than it should be able to hold?
– If a given amount of solute is dissolved in a solvent at a higher temperature, and the
solution is allowed to cool without being disturbed, the solute will remain in solution.
But the solution is unstable, and the solute will come out of solution (i.e. recrystallize) if the
solution is disturbed (e.g. by adding more solute, scratching the glass, etc.)
For some substances, recrystallization is exothermic, releasing heat to the surroundings.
→ Hot packs used to warm hands and feet in winter
For other substances, recrystallization is endothermic,
absorbing heat and making the surroundings colder.
→ Cold packs used for sports injuries
CHEM 161: Chapter 4 Review Notes v0916 p. 4 of 10 4.4 ELECTROLYTES AND NONELECTROLYTES
Electrolytes and electrical conductivity
– If a solution conducts electricity, it contains ions
– A solution that contains many ions is a strong electrolyte.
→ Light bulb burns brightly in a light bulb conductivity apparatus.
– A solution that contains only a few ions is a weak electrolyte.
→ Light bulb burns dimly in a light bulb conductivity apparatus.
– A solution that contains only a no ions is a nonelectrolyte.
→ Light bulb does not light in a light bulb conductivity apparatus.
CHEM 161: Chapter 4 Review Notes v0916 p. 5 of 10 strong electrolytes: substances that are good conductors of electricity
– These substances break up to produce many ions in water
→ many ions are present to move electrons/conduct electricity → strong electrolyte
For example,
NaCl(s)
or simplified
HO
""2"#
Na+(aq) + Cl–(aq)
+2
–
O
Ba(OH)2(s) "H
"2"# Ba (aq) + 2 OH (aq)
HBr(aq) + H2O(l) → H3O+(aq) + Br–(aq)
HBr (aq) → H+(aq) + Br–(aq)
– Examples: strong acids, strong bases, all soluble ionic compounds
weak electrolytes: substances that are weak/poor conductors of electricity
– These substances mostly remain intact as compounds, producing very few ions in water
→ only a few ions are present to move electrons/conduct electricity
→ weak electrolyte
O
Mg(OH)2(s) "H
"2"# Mg(OH)2(s)
HNO2(aq) → HNO2(aq)
For example,
– Examples: weak acids, weak bases, insoluble ionic compounds
nonelectrolytes: substances that cannot conduct electricity
– These molecules never break down into ions.
– They always remain intact as neutral molecules that have no charge
→ no ions to move electrons/conduct electricity
For example,
C12H22O11(s)
HO
""2"#
C12H22O11(aq)
– e.g., sugar (e.g. sucrose), ethanol (C2H5OH), and all other molecules that are not acids
Know the following acids and bases. All other acids and bases are weak!
Strong Acids
Strong Bases
HCl, HBr , HI, HNO3, HClO4, H2SO4
LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
Strong acids and bases dissolve in water to form many ions (or species) in solution.
For example,
HNO3(aq) +
H2O(l) →
Ca(OH)2(aq) →
H3O+(aq) + NO3–(aq)
Ca2+(aq) + 2 OH–(aq)
Note: H2SO4(aq) is a strong acid and diprotic (able to release 2 H+ ions), but it generally
ionizes to release only one H+ ion in water:
or simplified
H2SO4(aq)
H2SO4(aq)
+ H2O(l) → H3O+(aq) + HSO4–(aq)
→ H+(aq) + HSO4–(aq)
Recognize that in water H2SO4(aq) releases only one proton (not both protons)!
CHEM 161: Chapter 4 Review Notes v0916 p. 6 of 10 Ex. 1: Label each of the following as an acid, ionic compound, or neither then classify each
as a strong electrolyte, weak electrolyte, or nonelectrolyte:
acid, ionic compound, or neither
strong, weak, or nonelectrolyte
HI
Mg(OH)2
H2SO3
Sr(OH)2
ZnSO4
Al(NO3)3
C2H5OH
HNO3
(NH4)3PO4
H2CO3
Ex. 2: Draw each strong electrolyte broken up into individual ions in solution and each weak
electrolyte and nonelectrolyte remaining intact as a compound when in solution:
HI(aq)
Mg(OH)2
H2SO3
Sr(OH)2
ZnSO4
Al(NO3)3
C2H5OH
HNO3
(NH4)3PO4
H2CO3
CHEM 161: Chapter 4 Review Notes v0916 p. 7 of 10 MOLECULAR, IONIC, AND NET IONIC EQUATIONS
molecular equation: equation showing reactants and products as compounds
total/complete ionic equation:
– shows strong electrolytes as individual ions while all solids, liquids, gases, and weak
electrolytes remain intact as compounds
spectator ions: ions that do not form solids, liquids, gases, weak electrolytes
– appear on both sides of total ionic equation as ions
net ionic equations:
show only solids, liquids, gases, weak electrolytes (weak acids and
weak bases), and ions undergoing a chemical change/reaction
– excludes spectator ions
Guidelines for Writing Net Ionic Equations
1. Balance the chemical/molecular equation.
2. Convert the molecular equation to total ionic equation
– Leave solids, liquids, gases, and weak acids and bases as compounds
– Show strong acids and all aqueous ionic compounds as ions in solution.
3. Cancel spectator ions to get net ionic equation
– If canceling spectator ions eliminates all ions → NO REACTION (NR)
– If coefficients can be simplified, do so to get the lowest ratio.
4. Make sure total charges on both sides of the equation are equal.
Write the net ionic equation for each of the following:
a. molecular:
K2CO3(aq) +
Ca(NO3)2(aq) →
KNO3(aq) +
CaCO3(s)
total
ionic
eq.:
net
ionic
eq.:
Draw the substances indicated in the beakers below:
+
K2CO3(aq)
→
Ca(NO3)2(aq)
CHEM 161: Chapter 4 Review Notes v0916 after mixing
p. 8 of 10 b. molecular:
NaCl(aq) +
Ba(NO3)2(aq) →
BaCl2(aq) +
NaNO3(aq)
total
ionic
eq.:
net
ionic
eq.:
Draw the substances indicated in the beakers below:
+
NaCl(aq)
c. molecular:
→
Ba(NO3)2(aq)
HNO3(aq) +
after mixing
Sr(OH)2(aq) →
total
ionic
eq.:
net
ionic
eq.:
Draw the substances indicated in the beakers below:
+
HNO3(aq)
→
Sr(OH)2(aq)
CHEM 161: Chapter 4 Review Notes v0916 after mixing
p. 9 of 10 d. molecular:
HCl(aq) +
NaHCO3(aq) →
total
ionic
eq.:
net
ionic
eq.:
Draw the substances indicated in the beakers below:
+
HCl(aq)
e. molecular:
→
NaHCO3(aq)
Mg(s) +
after mixing
Al(NO3)3(aq) →
total
ionic
eq.:
net
ionic
eq.:
Draw the substances indicated in the beakers below:
+
Mg(s)
→
Al(NO3)3(aq)
CHEM 161: Chapter 4 Review Notes v0916 after mixing
p. 10 of 10