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Types of Chemical Reactions
PRE-LAB:
There are many kinds of chemical reactions and several ways of classifying them. One popular and useful
method is to classify reactions into four major types. They are: (1) direct combination, or synthesis; (2) decomposition;
(3) single replacement; and (4) double replacement, also known as exchange of ions. Not all chemical reactions can
be put into one of these categories. However, many can.
In a synthesis reaction, two or more substances combine to form a more complex substance. Equations for
synthesis reactions have the general form A + B  AB. An example of such a reaction is the formation of water from
its constituent elements: 2H2 + O2  2H2O.
A decomposition reaction is exactly the opposite of synthesis reaction. In a decomposition reaction, a
compound breaks down into two or more simpler substances (elements or simpler compounds). The general form of
the equation for a decomposition reaction is 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 equation is X + YB  XB + Y. In reactions in which one nonmetal replaces
another nonmetal, the general form is X + AY  AX + Y. The following equations illustrates the first of these types of
single replacement reactions:
Zinc metal replaces copper (H) ion:
Zn(s) + CuSO4 (aq)  ZnSO4 (aq) + Cu(s)
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 equation AB + CD  AD + CB. Most
‘replacement’ reactions (both single and double) take place in aqueous solutions containing free ions. In a double
replacement, one of the products formed can be a precipitate, an insoluble gas, or water.
All of the types of reactions discussed here may be represented by balanced chemical equations. Reactions
involving ion exchanges may also be represented by ionic equations. In this investigation you will be concerned only
with chemical formulas and equations. In a balanced equation, the number of atoms of any given element must be the
same on both sides of the equation. Multiplying the coefficient times the subscript of an element must yield the same
product on both sides of the balanced equation.
In this experiment you will observe examples of the four types of chemical reactions described here. You will
be expected to write and balance the equations representing the observed reactions.
PURPOSE:
Observe some chemical reactions and identify reactants and products of those reactions. Classify the
reactions and write balanced equations.
EQUIPMENT:
Burner
Crucible tongs
Micro spatula
Test tubes
Test tube holder
Test tube rack
Wood splints
Sandpaper
MATERIALS:
Zinc, mossy
Copper wire, 10cm
Magnesium ribbon, 5 cm
Copper (II) carbonate
3M Hydrochloric Acid
1M Copper (II) sulfate
0.1M Zinc acetate
0.1M Sodium phosphate
1M Sodium sulfite
Evaporating dish
Safety glasses
PROCEDURE:
A: Synthesis
1. Use fine sandpaper to clean a piece of copper wire until the wire is shiny. Examine the
wire and note its appearance in the data table.
2. Using crucible tongs, hold the wire in the hottest part of the burner flame for 1-2 minutes.
Examine the wire and note any change in its appearance caused by heat.
3. Place an evaporating dish handy to the base of the burner. Examine a piece of
magnesium ribbon. Using 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 what is left of it in the evaporating dish. Examine this product thoroughly and
record in the data table.
B. Decomposition
1. Place two heaping micro spatulas of copper (II) carbonate in a clean, dry test tube. Note
the appearance of the sample. Record in data table.
2. Using a test tube holder, heat the CuCO3 in a burner flame for about 3 minutes (until it is
black). Extinguish the flame and insert a burning wood splint half way into the test tube to
test for the presence of carbon dioxide gas. CO2 will put the flame out. Note any change in
the appearance of the material in the test tube. Record your observations in the data table.
C. Single Replacement
1. Stand a clean, dry test tube into a rack. Add about 5ml of 3M hydrochloric acid to the tube.
BE CAREFUL WITH ACIDS! Carefully drop a small piece of zinc metal into the acid in the
test tube. Observe and record what happens.
2. Using a test tube holder, invert a second test tube over the mouth of the first test tube.
Remove the inverted tube after about 30 seconds and quickly insert a burning wood splint
into the mouth of the tube. (A ‘pop’ indicates the presence of hydrogen gas). Note the
appearance of the substance in the first test tube.
3. Add about 5ml of 1M copper (II) sulfate solution to a clean dry, test tube. Place a small
piece of zinc metal in the solution. Wait about 5 minutes. Note the appearance of the
solution and the zinc before and after the reaction.
D. Double Replacement
1. Add about 2ml of 0.1M zinc acetate to a clean, dry test tube. Next, add about 2ml of 0.1M
sodium phosphate solution to the same test tube. Observe what happens and note any
changes in the mixture.
2. Add about 5ml of 1M sodium sulfite solution to a clean, dry test tube. To this solution, add
about 1ml of 3M HCl. Observe the odor given off by the mixture by wafting some of the gas
toward your nose. DO NOT SMELL THE GAS DIRECTLY!
OBSERVATIONS and DATA:
Reaction
Type
Reactants
Before Reaction
After Reaction
Cu
Synthesis
Mg
Decomposition
Single
Replacement
Double
Replacement
CuCO3
Zn + HCl
Zn + CuSO4
Zn(C2H3O2)2
Na2SO3 + HCl
CHEMICAL EQUATIONS:
You must write out each of the reactions using words first. Then you must convert to the
actual formula and balance each reaction. There are a total of 7 seven reactions.
Remember that in the synthesis reactions, one of the reactants is oxygen.
QUESTIONS:
1. In this experiment, what method was used to test for the presence of CO2 gas? Explain.
2. What test was used to check for the presence of hydrogen gas? Explain.
3. Balance the equations below and identify the type of reaction represented by each:
a. AgNO3(aq) + Cu(s)  Cu(NO3)2(aq) + Ag(s)
___________________
b.
BaCl2(aq) + Na2SO4(aq)  BaSO4(s) + NaCl(aq)
___________________
c.
Cl2(g) + NaBr(aq)  NaCl(aq) + Br2(l)
___________________
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)
___________________
REACTIONS: DO NOT COPY THIS!
Synthesis:
Cu + O2  CuO
Mg + O2  MgO
Decomposition:
CuCO3  CuO + CO2
Single Replacement:
Zn + HCl  ZnCl2 + H2
Zn + CuSO4  ZnSO4 + Cu
Double Replacement:
Zn(C2H3O2)2 + Na3PO4  NaC2H3O2 + Zn3(PO4)2
Na2SO3 + HCl  NaCl + H2O + SO2