Name(s)_____________________________________ Date ______________ Period ___
Types of Chemical Reactions Lab
The six types of chemical reactions are: synthesis, decomposition, single
displacement, double displacement, acid-base, and combustion.
In this lab, we will be doing examples of each of these types of reactions.
Important note: You should wear goggles during all sections of this
lab, as there are many dangerous chemicals in use.
Section 1: Synthesis Reaction
When chemists work with magnesium metal, they are very careful about how it is
handled. As you know, magnesium is an alkaline earth metal, so we would expect it to
be highly reactive. One of magnesium’s dangerous reactions is its reaction with oxygen
in the atmosphere to form magnesium oxide. This reaction gives off a great deal of light
and heat, and is started by placing the magnesium over a Bunsen burner flame. This is
the reaction we’re going to be doing today.
You may think that because we are using fire, this is actually a combustion reaction.
Actually, it doesn’t fit the definition of a combustion reaction. Even though oxygen is a
reactant and heat is generated, carbon dioxide and water are not formed. Instead, the
magnesium metal combines with oxygen to form magnesium oxide. Because two simple
compounds (Mg and O2) combine to form a more complex one (MgO), this is classified
as a synthesis reaction.
Procedure:
1.
Obtain a small piece of magnesium ribbon from the instructor.
2.
Light a Bunsen burner, making sure that it has been adjusted so a
bright blue cone of flame is visible.
3.
Using your crucible tongs, hold the magnesium ribbon directly over the
blue cone of the Bunsen burner flame until the reaction starts. Don’t
worry – you’ll know when it happens. Write down your observations
here:
4.
When the reaction has finished, clean up the laboratory station by
sweeping the magnesium oxide residue into the trash. Make sure that
you don’t touch the end of the crucible tongs – it will still be very hot!
Section 1 question: Write the chemical equation for the synthesis of magnesium
oxide from magnesium and oxygen gas:
Section 2: Decomposition Reaction
Some of the most violent chemical reaction are decomposition reactions. Sodium azide is
the chemical in airbags that spontaneously decomposes into sodium nitride and nitrogen
gas when sparked with an electrical charge. In this section, we will see a very common
decomposition reaction.
You’ve noticed that soda starts bubbling when you open the bottle, even though there
was no bubbling before the bottle was opened. This is due to the decomposition of
carbonic acid, H2CO3, into water and carbon dioxide. When the bottle is closed, pressure
inside the bottle keeps the reaction from occurring. When you open the bottle, pressure is
released and the reaction starts. When the bottle goes flat, all the carbonic acid has
completely reacted and the reaction is over.
Procedure:
1.
Using a spatula, place a small amount of sodium carbonate, Na2CO3,
into a clean, dry 50 mL beaker.
2.
Using a graduated cylinder, pour 10 mL of hydrochloric acid, HCl, into
the same 50 mL beaker.
3.
Write down your observations here:
4.
Clean up – the beaker may be cleaned by pouring the contents into
the sink and rinsing with water.
Section 2 question: When sodium carbonate and hydrochloric acid are
combined, the make carbonic acid, which then decomposes. Write the equation
for the decomposition of carbonic acid, H2CO3, into water and carbon dioxide.
Section 3: Single displacement reactions
Single displacement reactions are very important in the area of electrochemistry.
Without single displacement reactions, we wouldn’t have batteries of any kind.
In the reaction you will be observing, zinc, Zn, reacts with hydrochloric acid, HCl, to
form hydrogen gas and zinc chloride. When this reaction takes place, electrons move
from zinc to hydrogen. In a battery, these electrons are used to produce electricity.
Procedure:
1.
Fill a small Erlenmeyer flask to approximately the 10 mL mark with
hydrochloric acid, HCl.
2.
Place 1 small piece of zinc metal into the HCl. Write down your
observations here:
3.
Clean up – clean up the lab by pouring the zinc and hydrochloric acid
into a labeled waste beaker. Make sure to get any unreacted zinc out
of the flask.
Section 3 questions: Write the equation for the reaction of hydrochloric acid with
zinc to form zinc chloride and hydrogen gas.
What do you think the bubbles were that you saw being formed?
Section 4: Double displacement reactions
Double displacement reactions are extremely common in chemistry. Many common
reaction in industry and nature involve double displacement reactions. For example, the
shells of many sea animals are made of calcium carbonate, formed from double
displacement reactions within the animals.
The double displacement reaction you will do today was once instrumental in the
manufacture of paints for household products. You will no doubt be able to guess what
extremely common school product was painted with this pigment when you see it being
formed.
Procedure:
1.
In a watch glass, place 5 drops of potassium iodide, KI, using the
labeled dropper.
2.
To this watch glass, add 5 drops of lead (II) nitrate, Pb(NO3)2, using
the labeled dropper. Write your observations here:
3.
Clean up – pour the mixture into a labeled waste beaker. Rinse off the
watch glass with water after disposing of precipitate.
Section 4 Questions:
1)
What common school product do you think was painted with this
pigment?
2)
Why do two colorless solutions form a colored compound when they
are combined? What do you think has happened?
3)
Write the equation for the reaction of potassium iodide, KI, with lead
(II) nitrate, Pb(NO3)2, to produce lead (II) iodide with potassium
nitrate, KNO3.
Section 5: Acid-base reactions
Acid-base (neutralization) reactions are responsible for many reactions in biochemistry
and atmospheric chemistry. One example of acid-base chemistry is acid rain. Acid rain
occurs when acidic gases are released by power plants and dropped hundreds of miles
from their source, killing fish and plants.
In this section, you will see the acid-base reaction of hydrochloric acid, HCl, with sodium
hydroxide, NaOH.
Procedure:
1.
Pour 5 drops of hydrochloric acid, HCl, into a watch glass. Add one
drop of indicator solution (phenolphthalein) to the watch glass. The
color you see indicates the presence of an acid. What color indicates
that an acid is present?
2.
Slowly add sodium hydroxide, NaOH, to the watch glass containing
HCl, drop by drop, until the color of the solution changes. The new
color indicates base is present in the solution. What color is the new
solution?
3.
Clean up – rinse the solution on the watch glass with water down the
drain.
Section 5 Questions:
1.
Antacids such as Tums, Rolaids, and Maalox work by the same means
that baking soda does. Do you think this explains why they work so
quickly? Explain.
2.
Acid-reducing medications such as Pepcid AC, Tagament HB, and Axid
AR work by a completely different mechanism that does not neutralize
stomach acid. Instead, these medications work by making the
stomach secrete less acid in the first place. Do you think this explains
why they work so slowly? Explain.
3.
Write the equation for the reaction of hydrochloric acid, HCl, with
sodium hydroxide, NaOH, to form sodium chloride, NaCl, and water.
Section 6: Combustion reactions
Modern life depends on combustion reactions. The energy we use in our homes is
generated by power plants that burn coal. The energy that powers our cars is generated
by the combustion of gasoline. The heat that cooks food on a gas stove is generated by
the combustion of natural gas. Without combustion reactions, there would be nowhere
near enough energy to keep society running.
One of the main things we as a society are trying to do is to find new sources of energy
that don’t require the combustion of non-renewable resources such as coal, gas, oil, or
wood. Unfortunately, solar power is not yet efficient enough to produce industrial
amounts of power, wind power is not reliable, hydroelectric power has already been fully
exploited, and environmental activists have kept nuclear power from being adequately
utilized. Until technical or social hurdles can be removed, we will be dependent on a
shrinking supply of fuel to run our society.
Methanol is a fuel that can be used to power both family and high-performance
automobiles. We will be observing the combustion of methanol, CH3OH, in this section.
Procedure:
1.
Pour about 10 drops of methanol, CH3OH, into a watch glass.
2.
Using crucible tongs to hold the match, carefully light the methanol,
making sure to keep your hand away from the fire. Write your
observations for this reaction here:
Section 6 questions:
1.
What did the methanol fire look like? Did it look like other flames you
have seen before, or were there some differences? Explain.
2.
Methanol fires are far less hot than gasoline fires. This makes them
safer to use in automobiles, but less capable of producing large
amounts of energy. Keeping this in mind, do you think that methanol
is a good source of fuel for automobiles? Explain.
3.
Write the reaction for the combustion of methanol with oxygen gas to
produce carbon dioxide and water.