Types of Chemical Reactions
Pre-Lab Discussion
There are many kinds of chemical reactions and several ways to classify them.
One useful method classifies reactions into four major types. These are: 1) Direct
combination or synthesis; 2) Decomposition, or analysis; 3) Single Replacement; and 4)
Double Replacement or exchange of ions. Not all reactions can be put into one of these
categories. Many, however, can.
In a synthesis reaction, two or more substances (elements or compounds)
combine to form a more complex substance. Equations, for synthesis reactions have the
general form A + B AB. For example, the formation of water from hydrogen and
oxygen is written 2H2 + O2  2H2O.
A decomposition reaction is the opposite of a synthesis reaction.
In
decomposition, a compound breaks down into two or more simpler substances (elements
or compounds). Equations for decomposition reactions have the form AB  A + B. The
breakdown of water into its elements is an example of such a reaction: 2H2O  2H2 +
O2.
In a single replacement reaction, one substance in a compound is replaced by
another, more active, substance (element). Equations for single replacement reactions
have two general forms. In reactions in which one metal replaces another metal, the
general reaction is X + YB  XB + Y. In those in which one nonmetal replaces another
nonmetal, the general form is X + AY  AX + Y. The following equations illustrate
these types of reactions:
Zinc metal replaces copper(II) ion:
Zn(s) + CuSO4 (aq)  ZnSO4 (aq) + Cu (s)
Chlorine (a nonmetal) replaces bromide ions:
Cl2 (g) + 2KBr (aq)  2KCl (aq) + Br2 (l)
In a double replacement reaction, the metal ions of two different ionic
compounds can be thought of as “replacing one another”. Equations for this type of
reaction have the general form AB + CD  AD + CB. Most replacement reactions, both
single and double, take place in aqueous solutions containing free (dissolved) ions. In a
double replacement reaction, one of the products is a precipitate (solid), and insoluble
gas, or water. An example is the reaction between silver nitrate and sodium chloride in
which the precipitate silver chloride is formed:
AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
PRE LAB QUESTIONS
ANSWER THESE IN YOUR LAB NOTEBOOK AFTER YOU’VE WRITTEN
THE PURPOSE.
1) Define & Describe each of the four main types of reactions.
2) Provide an example of each of the four main types of reactions. Please choose a
different one from that provided in the pre-lab discussion. You should refer to section
8.2 of your text for help with this question.
3) List at least 2 safety precautions you must consider during this lab.
Purpose:
Observe some chemical reactions and identify reactants and products of
those reactions. Classify the reactions and write balanced equations.
Materials & Equipment
• Bunsen Burner
• Crucible Tongs
• Scoopula
• Test Tubes
• Test Tube Rack
• Test Tube Clamp
• Wood Splint
• Evaporating Dish
• Safety Goggles
• Zinc
• Copper Wire (Cu)
• Magnesium Ribbon
• Copper (II) Carbonate
• Hydrochloric acid (HCl)
• Copper (II) Sulfate
• Zinc acetate
• Sodium Phosphate
• Sodium Sulfite
SAFETY
In this investigation, you will be working with open flames, heating chemicals, handling
acids, and producing gaseous products. Burning magnesium produces a very bright, hot flame.
Make sure you hold the burning metal at arm’s length and DO NOT LOOK DIRECTLY AT IT!!
Remember never to smell a chemical directly, but to waft gases toward your nose.
**Please use the two-column format in your lab notebook! The left column is for the
procedures; the right column is for the observations.
PART A
SYNTHESIS
1.
Using crucible tongs, hold the copper wire in the hottest part of a Bunsen burner flame
for 1 – 2 minutes. Examine the wire and note any change in its appearance caused by
heating.
2.
Place an evaporating dish near the base of the Bunsen burner. Examine a piece of
magnesium ribbon. Using crucible tongs, hold the sample in the burner flame until the
magnesium starts to burn. DO NOT LOOK DIRECTLY AT THE FLAME!! HOLD
THE BURNING MAGNESIUM AWAY FROM YOU AND DIRECTLY OVER THE
EVAPORATING DISH. When the ribbon stops burning, put the remains in the
evaporating dish. Examine the product carefully.
PART B
DECOMPOSITION
1.
Place 2 heaping scoops of copper (II) carbonate in a clean, dry test tube. Note the
appearance of the sample.
2.
Using a test tube holder, heat the copper (II) carbonate strongly for about 3 minutes.
Extinguish the flame and then insert a burning wood splint into the test tube. If carbon
dioxide gas is present, it will put the flame out. Note any change in the appearance of the
residue in the test tube.
PART C
SINGLE REPLACMENT
1.
Stand a clean, dry test tube in the test tube rack. Add about 5 mL of hydrochloric acid
(HCl) to the tube. Now carefully drop a small piece of zinc metal into the acid in the test
tube. Cover the tube with a small piece of cardboard. Observe and record what happens.
2.
Light a wood splint and insert the burning splint into the mouth of the tube. The ‘pop’,
‘squeak’, or ‘bark’ indicates the presence of hydrogen gas. Note the appearance of the
substance in the reaction test tube.
3.
Add about 1 mL of copper (II) sulfate solution to a clean, dry test tube. Place a small
amount of zinc metal in the solution. Note the appearance of the solution and the zinc
before and after the reaction.
PART D
DOUBLE REPLACEMENT
1.
Add about 2 mL of zinc acetate to a clean, dry test tube. Next, add about 2 mL of sodium
phosphate solution to the test tube. Observe what happens and note any changes in the
mixture.
2.
Add about 2 mL of sodium sulfite solution to a clean, dry test tube. To this solution, add
about 1 mL of HCl (hydrochloric acid). Note the odor given off by wafting some of the
gas toward your nose. DO NOT SMELL THE GAS DIRECTLY!!
POST LAB DISCUSSION QUESTIONS
You will complete these in your lab notebook AFTER completion of the lab. It is
acceptable to print these out and paste into your lab notebook. Leave plenty of space to answer
the questions.
Equations
For each of the following:
a)
Balance each of the equations.
b)
Write the names of the reactant(s) and product(s) below the molecular equation.
Part A Synthesis
1.
Cu (s)
+
O2 (g)

CuO (s)
2.
Mg (s)
+
O2 (g)

MgO

CuO (s) +
CO2 (g)
(s)
Part B Decomposition
3.
CuCO3 (s)
Part C Single Replacement
4.
Zn (s)
+
HCl (aq)

ZnCl2 (g)
+
H2 (g)
5.
Zn (s)
+
CuSO4 (aq)

ZnSO4 (aq)
+
Cu (s)
Part D Double Replacement
6.
Zn(C2H3O2)2 (aq) +
Na3PO4 (aq)

NaC2H3O2 (aq) +
Zn3(PO4)2 (s)
7.
Na2SO3 (aq)
+

NaCl (aq)
H2O (l) + SO2 (g)
HCl
+
Conclusion Questions
1.
In this experiment, what method was used to test for the presence of carbon dioxide gas?
2.
What test was used to identify hydrogen gas?
3.
Balance the following equations and identify the type of reaction it represents.
a)
AgNO3 (aq) + Cu (s)

b)
BaCl2 (aq)
+
Na2SO4 (aq)
 BaSO4 (s)
c)
Cl2 (g)
+
NaBr (aq)

NaCl (aq)
d)
KClO3 (s)

KCl (s)
+
O2 (g)
e)
AlCl3 (aq)
+
NH4OH (aq)
 NH4Cl (aq) + Al(OH)3 (s)
f)
H2 (g) +
O2 (g)  H2O (g)
Cu(NO3)2 (aq) + Ag (s)
+
NaCl (aq)
+
Br2 (l)