A STUDY OF CHEMICAL REACTIONS AND THEIR CLASSIFICATION
BACKGROUND
Chemical reactions involve changes in the electronic structure of the atoms or compounds that
take part in the reactions. In general, there are certain requirements, which must be met in order
that chemical reactions can occur. First of all, it is necessary that the reactants be in good contact
with each other. Reactions carried out in the liquid and gaseous states afford the best media for
mixing the reactants, however, reactions carried out between substances in the solid state can be
carried out in many cases under the proper conditions.
There are also energy requirements that must be met in order for the reaction to take place.
Reactions which produce energy when they occur (exothermic) are ordinarily easier to carry out than
those that require energy (endothermic). Many reactions even though exothermic occur so slowly
(rate order) that it is not practical to carry them out. This is because there is an initial energy barrier
that must be overcome in order for the reaction to go spontaneously (thermodynamically – enthalpy
and entropy considered). Often times, this type of reaction can be speeded up by adding heat
(activation energy Ea), or by introducing a catalyst. There are other conditions, which determine
whether specific reactions can or cannot be carried out.
There are many ways of classifying chemical reactions. No scheme is all inclusive, since there
are over 100 elements and they can interact in many unusual ways. However, for elementary work, four
types of reactions are generally recognized:
1. Oxidation Reduction reactions
a. Combustion
b. Single Replacement
c. Combination (possibly)
2. Decomposition reactions (possibly redox)
3. Double replacement reactions also known as precipitation reaction and/or
neutralization reaction
PROCEDURE
NOTE: this is a qualitative experiment not quantitative. Masses and volumes need not be measured
precisely. You need to record all qualitative observations. It is advised to split your laboratory graph
paper book pages into three vertical columns. Draw the procedure for all of the experiments in the
far left column, the observations in the middle column, and then answer the questions in the far right
column.
A. Combination
1. THE UNION OF ONE ELEMENT WITH ANOTHER
Hold the strip of magnesium ribbon with crucible tongs in the flame of a Bunsen burner.
Caution: Do not look directly at the burning magnesium, look through cobalt glass.
2. THE UNION OF AN ELEMENT WITH A COMPOUND
To a few drops of a solution of sodium iodide (NaI), add a small crystal of iodine (I2) and stir.
The wine-colored solution contains sodium triiodide (NaI3).
B. Decomposition This type of chemical reaction involves the breaking down of a compound into two
or more simpler substances (possibly elements).
3. METALLIC CHLORATES (IN FUMEHOOD)
Put potassium chlorate crystals, KClO3 into a dry test tube to a depth of about 0.5 cm and heat
strongly. As soon as bubbles begin to be evolved form the molten material, put a glowing splint
part way down the tube. Caution – the molten crystals are very hot and the gas produced is
very flammable.
4. METALLIC CARBONATES
Now put calcium carbonate (CaCO3) into a test tube to a depth of 0.5 cm and heat this
compound strongly. Put a glowing splint into the test tube and observe.
5.. METALLIC HYDROXIDES
Place copper (II) hydroxide Cu(OH)2 into a test tube to a depth fo 0.5 cm and heat this
compound strongly. Put a glowing splint into the test tube and observe.
IN FUMEHOOD – Go to the hood and carefully observe the compound ammonium hydroxide
(NH4OH) observe by wafting the odor of the gas. This is ammonia gas (NH3).
****. ACIDS
(No experiment here, note equation) Certain acids, when heated, decompose into nonmetallic
oxides and water.
H2CO3 
H20 + CO2
H2SO3 
H20 + SO2
6. METALLIC OXIDES
Put a small scoop of lead(IV) oxide (PbO2) in a test tube and heat in a Bunsen burner flame. Put
a glowing splint part way down into the test tube. The PbO2 decomposes to PbO.
7. DECOMPOSITION BY EXPOSURE TO LIGHT
Put one drop of hydrochloric acid on a piece of filter paper. Now allow one drop of silver
nitrate (AgNO3) to fall on the spot moistened by the acid. Allow the paper to remain exposed
to light for a few minutes. (Sunlight works best). The darkening of the spot is due to the
decomposition of the silver chloride into dark, finely-divided silver and chlorine.
C. Replacement
8. THE REPLACEMENT OF ONE METAL BY ANOTHER
Drop a few pieces of granulates zinc into a test tube containing 1mL of copper sulfate (CuSO 4)
solution. Stir thoroughly for one minute, let it sit and observe for a total of 10 minutes. Be
sure to perform other experiments as you wait.
9. THE DISPLACEMENT OF HYDROGEN OF METALS
Place a small piece of zinc into a test tube add enough hydrochloric acid (HCl) to cover the
metal and observe.Those metals which are listed above hydrogen in the activity series will
displace hydrogen from solution under the proper conditions.
10. THE DISPLACEMENT OF NONMETALS BY NONMETALS
Perform in the FUMEHOOD: Place some sodium iodide (NaI) solution into a test tube now go
to the fume hood and add bromine water and some hexane (all about equal amounts). Shake
thoroughly and note the color of the hexane layer. A violet color is due to free iodine, I 2.
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**Repeat this experiment using sodium bromide solution, go to the fume hood and add chlorine
water and a few drops of hexane has been added, observe.
D. Double Replacement
11. FORMATION OF A PRECIPITATE
Place some silver nitrate solution into a test tube. Add some sodium chloride solution. Notice
before mixing both salts are soluble, observe what occurs when these two solutions are mixed.
12. FORMATION OF A GAS
When certain compounds such as carbonic acid, sulfurous acid, and ammonium hydroxide are
formed as products of a reaction, they decompose to form the gases CO2 and NH3
respectively. This brings about the completion of the reaction.
Place sodium bicarbonate (NaHCO3) solution into a test tube. Slowly add hydrochloric acid. As
they mix make observations. Check with a glowing splint to determine what gas is being
produced.
To finish the laboratory report the following is required:
Conclusion Statement:
Discussion of Theory: Choose two reactions and explain the theory related to those two
reactions thoroughly – be sure to focus on theory not procedure.
Questions / Results:
A. Combination
1. The union of one element with another
Complete and balance the equations and answer the following questions.
a. Mg + O2 
b. Mg + N2 
c. What are the reactants and the physical states of the reactants?
2. The union of an element with a compound
Write the equation for the union of sodium iodide and iodine.
B. Decomposition
3. Metallic Chlorates
a. Observations with the glowing splint.
b. Does the gas burn? Does the gas support combustion?
c. What gas do you think it is?
d. Write the chemical equation.
4. Metallic Carbonates
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a.
b.
c.
d.
Observations with the glowing splint.
Does the gas burn? Does the gas support combustion?
What gas do you think it is?
Chemical equation.
5. Metallic Hydroxides
a. Chemical equation for decomposition of NH4OH
****. Acids – Be sure to refer to this when writing equations at the end of the exercise.
6. Metallic Oxides
a. Observation with glowing splint.
b. Properties of gas evolved.
c. Chemical equation.
7. Decomposition by exposure to light
a. HCl + AgNO3  AgCl + ______________
b. Describe your observations
c. Chemical equation for the decomposition of AgCl
C. Replacement
8. The replacement of one metal by another
a. Give two observations that indicate a reaction is occurring.
b. Complete the equation: CuSO4 + Zn 
9. The displacement of hydrogen by metals
a. Write the equation for the reactions.
10. The displacement of nonmetals by nonmetals
a. What is the purpose of hexane?
b. Complete and balance he equation NaI + Br 2  __________ + __________
c. To what is the brown color due?
d. Write balanced chemical equations for the Redox that occurred.
e.
D. Double Replacement
11. Formation of a precipitate
a. Chemical equation.
b. Which is more soluble in water, silver nitrate or silver chloride?
c. How can you tell?
12. Formation of a gas
a. Observation of glowing splint
b. Properties of the gas.
c. What do you think the gas is?
d. Chemical equation: NaHCO3 + HCl  NaCl + ________________
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E. Complete and balance each of the following chemical equations: (HINT: the reaction type is
identified.)
1.
[R]
Zn + Cu(NO3)2 
8. [R]
Mg + H2SO4 
2.
[C]
C + O2 
9. [DR]
AgNO3 + KBr 
3.
[R]
NaI + Br2 
10. [D]

Ni(ClO3)2 
4.
[DR]FeCl3 + (NH4)2S  Fe2S3 +
11. [C]
P + I2  PI3
heat
heat
5.
[D]

SrCO3 
12. [R]
KI + Cl2 
6.
[C]
H 2 + O2 
13. [DR]
NaHCO3 + H2SO4 
7.
[DR]
KOH + CaCl2 
NO Sources of Error are required for this laboratory experience.
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