CHEMICAL REACTIONS AND EQUATIONS
INTRODUCTION
How can we tell when a chemical reaction has taken place? Often there will be heat or
light produced. There will always be at least one new substance formed, with different
properties from those of the starting material. Any of the following would be evidence of a
chemical reaction:
bubbles of gas
the solution turns cloudy and a precipitate forms
the solution changes color
the material bursts into flame
the mixture becomes hot or cold
tests on the material no longer give the same results.
PART I
DOUBLE REPLACEMENT REACTIONS
Metathetical reactions are sometimes called double-replacement reactions. In these
reactions two compounds exchange ions with each other. Metathetical reactions are usually
carried out in aqueous solution. The general formula for this type of reaction is
AC + BD → AD + BC
A. PRECIPITATION REACTIONS
In this type of metathetical reaction, a precipitate is formed. The precipitate is indicated
by a arrow pointing down or the physical state indicator (s). The formation of a precipitate may
be predicted by using solubility rules or a solubility chart. To classify the reaction as a
precipitation one, the two reactants must be aqueous solutions and at least one of the product is
water insoluble to form the precipitate (solid formation)
Examples:
AgNO3 (aq) + NaCl(aq)→ AgCl(s)↓ + NaNO 3 (aq)
In these reactions, all of the soluble compounds are considered dissociated into their ions. The
ions which are not involved in the precipitate are considered "spectator ions" and may be
eliminated to form the net-ionic equation.
complete (full) ionic equation
Ag+ (aq) + NO−3 (aq) + Na+ (aq) + Cl− (aq )→ AgCl(s) + Na+ (aq ) + NO−3 (aq )
net-ionic equation
Ag+ (aq) + Cl− (aq )→ AgCl(s)
PROCEDURES: Perform each of the following reactions. Write your observations in your
data sheet and write the molecular, complete ionic, and net-ionic equation for each reaction.
Indicate the precipitate.
1. To a dropperful of 0.1 M calcium nitrate in a test tube, add a dropperful of 0.1 M sodium
carbonate.
2. To a dropperful of 0.1 M magnesium sulfate in a test tube, add a dropperful of 0.1 M
sodium hydroxide.
3. To a dropperful of 0.1 M lead (II) nitrate in a test tube, add a dropperful of 0.1 M
potassium iodide.
B. ACID-BASE REACTIONS (NEUTRALIZATION REACTIONS)
In this type of metathetical reaction, heat is given off and a salt and water are formed. If
the solutions are dilute, the heat effect may not be noticeable and no visible change occurs.
Thus, we use an indicator like phenolphthalein to indicate that a reaction has occurred.
Phenolphthalein is pink in basic solution and colorless in acidic or neutral solutions.
1. Strong acids and strong bases are completely ionized in solution (100% ions).
Example:
HNO3 (aq ) + KOH ( aq)→ KNO3 (aq ) + H 2 O(l)
Complete ionic:
H+(aq) + NO3-(aq) + K+(aq) + OH-(aq) K+(aq) + NO3-(aq) + H2O(l)
net-ionic
H + (aq ) + OH − (aq )→H 2 O (l )
2. Metal carbonates are basics and the addition of an acid will result in the formation of
bubbles (evolving of carbon dioxide gas):
Molecular:
HNO3 (aq) + NaHCO3 (aq) NaNO3 (aq) + CO2 (g) + H2O (l)
Complete ionic:
H+(aq)+NO3−(aq)+ Na+(aq) + HCO3−(aq) Na+(aq)+NO3−(aq)+CO2 (g)+H2O(l)
net-ionic:
H+(aq) + HCO3−(aq) CO2 (g) + H2O (l)
PROCEDURES: Perform each of the following reactions. Write your observations in your
data sheet and write the molecular, complete ionic, and net-ionic equation for each reaction.
1. Add a dropperful of 0.1 M NaOH and one drop of phenolphthalein to a test tube. Note
the color. Add 0.1 M HCl drop by drop until the color changes. Feel the test tube. Can
you detect the evolution of heat?
2. Add a dropperful of 2.0 M sodium carbonate in a test tube. Add a dropperful of 1.0 M
hydrochloric acid.
PART II
COMBINATION REACTIONS
Combination reactions are those in which two or more elements (or simple compounds)
combine to form a more complex substance. The general formula for a combination reaction is
Many combination reactions involve the reaction of two elements to form a compound and
A+B → C
these are all redox reactions. Many elements react with oxygen to form oxides.
C + O 2 →CO 2
Some 4Na + O 2 → 2 Na2 O
combination reactions involve the reaction of two compounds to form another compound. These
are often not redox reactions. Metal oxides react with water to form metal hydroxides. The
presence of the hydroxide ion is detected with phenolphthalein.
Na2 O + H 2 O → 2NaOH
PROCEDURES: Perform each of the following reactions. Write your observations in your
data sheet and write the balanced equation for each reaction. Identify each reaction as redox or
non-redox.
1. Transfer a spatulafull of copper mesh into a dry clean crucible. Record the color and the
texture of the solid. Hold the crucible-containing copper by the crucible tong and heat the
copper using Bunsen burner. Record any change in your data sheet.
2. Add a dropperful of distilled water and a drop of phenolphthalein into a clean test tube
and record your observation. Add few crystal of calcium oxide into the test tube and
shake it well to dissolve. The phenolphthalein is only an indicator for the presence of
hydroxide ion and does not enter into the equation.
PART III
DECOMPOSITION REACTIONS
A decomposition reaction is the reverse of a combination reaction. It involves the
breakdown of a complex substance into simpler substances. The general equation for a
decomposition reaction is
C → A+B
Metal oxides decompose to the metal and oxygen gas. This is a redox reaction.
2HgO → 2Hg + O 2
Metal hydroxides decompose to the metal oxide and water. This is not a redox reaction.
Mg(OH )2 → MgO + H 2 O
PROCEDURES:
Perform each of the following reactions. Watch for evidence of the decomposition products.
Write your observations in your data sheet and write the equation for each reaction. Identify
each reaction as redox or non-redox.
1. Place a few crystals of copper(II)sulfate pentahydrate in a test tube. Clamp the tube and
heat in a horizontal position. One of the products is copper(II)sulfate. What is the other
one? This decomposition reaction is easily reversible. Add a dropperful of water to the
tube when it cools. What happens?
PART IV
SINGLE REPLACEMENT REACTIONS
A single replacement reaction is one in which one metal replaces a cation in a compound.
The general formula for this type of reaction is
A + BC → AC + B
Whether a single replacement reaction will occur may be predicted with the use of an activity
series. The higher the metal is in the activity series, the greater its tendency to ionize and
displace metals lower in the series. For example, calcium will ionize and displace iron form a
solution which contains an iron salt, but iron will not displace the calcium in a calcium salt.
Ca(s ) + FeCl 2 (aq )→CaCl2 ( aq ) + Fe( s )
Fe( s ) + CaCl 2 (aq )→ no reaction
PROCEDURES: Perform each of the following reactions. Write your observations in your
data sheet and write the equation for each reaction. All of these reactions are redox reactions.
1. Place a piece of zinc in a test tube. Add about 2.0 mL of 6 M HCl and allow the zinc to
effervesce. Ignite a wooden splint in a Bunsen burner flame and hold this flame to the
mouth of the test tube. If hydrogen is generated as one of the products, you will hear a
"pop". Note that the test for hydrogen is a combination reaction. What is the hydrogen
combining with?
2. a) Place a small piece of zinc in a test tube containing about 2.0 mL of copper(II) sulfate
solution.
b) In a second test tube, place a small piece of copper in about 2.0 mL of zinc chloride
solution. Note the original appearance of the metals and colors of solutions. Put these
test tubes aside for at least 5 minutes and then write down your observations.
CLEAN-UP
1. Dispose of solids in the waste container under fume hood. Acid/Base solutions may be
flushed down the hood sink with excess water.
2. Wash all of your test tubes with a test-tube brush and soap, rinse with distilled water and
invert in a test tube rack to dry.
3. Check to see that all chemicals are properly closed and returned to their proper tray.
4. Check balance and hood areas for chemicals, spatulas etc.
5. Wash off your work areas.
6. Wash your hands.
Solubility rules
1. Salts containing Group I elements are soluble (Li+, Na+, K+, Cs+, Rb+). Exceptions to this
rule are rare. Salts containing the ammonium ion (NH4+) are also soluble.
2. Salts containing nitrate ion (NO3-) are generally soluble.
3. Salts containing Cl -, Br -, I - are generally soluble. Important exceptions to this rule are
halide salts of Ag+, Pb2+, and (Hg2)2+. Thus, AgCl, PbBr2, and Hg2Cl2 are all insoluble.
4. Most silver salts are insoluble. AgNO3 and Ag(C2H3O2) are common soluble salts of
silver; virtually anything else is insoluble.
5. Most sulfate salts are soluble. Important exceptions to this rule include BaSO4, PbSO4,
Ag2SO4 and SrSO4 .
6. Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are
soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble.
Hydroxide salts of transition metals and Al3+ are insoluble. Thus, Fe(OH)3, Al(OH)3,
Co(OH)2 are not soluble.
7. Most sulfides of transition metals are highly insoluble. Thus, CdS, FeS, ZnS, Ag2S are all
insoluble. Arsenic, antimony, bismuth, and lead sulfides are also insoluble.
8. Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble.
Some other insoluble carbonates include FeCO3 and PbCO3.
9. Chromates are frequently insoluble. Examples: PbCrO4, BaCrO4
10. Phosphates are frequently insoluble. Examples: Ca3(PO4)2, Ag3PO4
11. Fluorides are frequently insoluble. Examples: BaF2, MgF2 PbF2.
Name ____________________ Station # ____ Date _______________
CHM 111 – Types of Chemical Reaction
Pre Lab Questions
1. Balance and classify each of the following reactions:
__ HgO __ Hg + __ O2
__ Na + __ H2O __ NaOH + __ H2
__ H2 + __ N2 __ NH3
__ Pb(NO3)2 + __ H2S __ PbS + __ HNO3
2. Write the balanced molecular, complete ionic and the net ionic equation for each
reaction (if any) when aqueous solutions of:
a) Na2CO3 and Ba(NO3)2 are mixed.
b) HCl(aq) and Ca(OH)2 (aq) are mixed.
Name ____________________ Station # _____ Date _____________
CHM 111 – Types of Chemical Reaction
REPORT SHEET
PART I.
Write observation, the molecular, complete ionic and net-ionic equations for each reaction.
A1:
Observation:
Molecular:
Complete ionic:
Net ionic:
A2:
Observation:
Molecular:
Complete ionic:
Net ionic:
A3:
Observation:
Molecular:
Complete ionic:
Net ionic:
B1:
Observation:
Molecular:
Complete ionic:
Net ionic:
B2:
Observation:
Molecular:
Complete ionic:
Net ionic:
PART II.
Write observation and the complete molecular equation for each reaction. Identify each reaction
as redox or non-redox.
1:
Observation:
Molecular Equation:
2:
Observation:
Molecular Equation:
PART III
Write observation and the complete molecular equation for the following reaction.
1:
Observation:
Molecular Equation:
PART IV.
Write observation and the complete molecular equation for each reaction. Identify each reaction
as redox or non-redox
1:
Observation:
Molecular Equation:
2a:
Observation:
Molecular Equation:
2b:
Observation:
Molecular Equation:
Name _________________ Station # _____ Date ___________
CHM 111 – Types of Chemical Reaction
POST LAB QUESTIONS
1. Balance the following reactions:
a._____FeCl3 + _____NH4OH _____Fe(OH)3 + _____NH4Cl
b. ____ Ag + ____ H2S + ____ O2 ____ Ag2S + ____ H2O
c. ____ CS2 + ____ Cl2 ____ CCl4 + ____ S2Cl2
d. ____ Al + ____ O2 ____Al2O3
2. Identify which species is reduced, which species is oxidized. Identify the oxidizing agent
and the reducing agent in the following redox reaction.
a) Cr2O7 2- (aq) + Cl- (aq) Cr3+ (aq) + Cl2 (aq)
b) Zn(s) + 2 AgNO3(aq) → Zn(NO3)2(aq) + 2 Ag(s)
c) C (s) + O2(g) CO2(g)
3. Write net ionic equations for the reactions that occur when aqueous solutions of the
following are mixed.
a. Ammonium sulfate and barium nitrate
b. Copper(II) chloride and sodium hydroxide
c. Lithium hydroxide and sulfurous acid.
