Download Expt 8B Equation Writing and Products

Experiment S-8B
Equation Writing and Predicting Products
Objective
At the completion of this experiment, the students will
 write chemical equations from the chemical reactions they observe.
 explore and learn the process of balancing an equation
Apparatus and Materials
Chemical splash goggles, lab apron, 2 pieces of Mg ribbon, tongs, lab burner, striker, watch
glass, 6 test tubes, graduated cylinder, 2.0M HCl, test-tube rack, test-tube holder, 3 wooden
splints, Cu foil, file, spatula, (NH4)2CO3, cobalt chloride paper, 3% H2O2, MnO2, 0.1 M KI,
0.1 M Pb(NO3)2
Theory of Concepts
If you examine a car that has been in a junkyard for a while, you will notice that it has
rusted. Rusting is a slow chemical reaction of the iron in the car with oxygen gas. If sodium is
put into water, a much more rapid chemical reaction occurs. Sodium reacts with water to produce
sodium hydroxide and hydrogen gas. During this reaction, enough heat is liberated to ignite the
hydrogen gas, causing it to explode.
Chemists observe what is happening in a chemical reaction and try to describe it in
language that is simple and clear. A chemical equation uses formulas and symbols to describe the
substances involved in a reaction, the physical state of the substance, the use of a catalyst (a
substance that speeds up a reaction without itself being consumed), and relative proportions., The
general form of an equation is:
REACTANTS  PRODUCTS
In this investigation you will perform a series of reactions and make careful observations
of the changes that occur. Using simple tests and your knowledge of chemistry, you will
determine the identity of the products. With this information, you will write chemical equations
to describe the reactions.
Procedures
1. Put on your goggles and lab apron. For each of the reaction, record in the Data Table
observations such as the appearance of the reactants; evidence that a chemical reaction
has taken place; the results of tests performed on any gases produced; the appearance of
the products; and any other relevant data.
2. Obtain a piece of magnesium ribbon light. Light the lab burner. Holding the magnesium
with your tongs, carefully place it in the lab burner flame. Hold the burning magnesium
ribbon over some wire gauze to catch any debris. CAUTION: Do not look directly at the
magnesium while it burns. Turn off the burner.
3. Place a test tube in the test tube rack. Have a second test tube ready in a test-tube holder.
Add 5-10 mL of a 3.0 M HCl to the first test tube. Drop a 2-cm piece of magnesium
4.
5.
6.
7.
ribbon into the acid. CAUTION: HCl is corrosive. Invert the second test tube over the
mouth of the first test tube. When the reaction appears to have ended, light a wooden
splint and quickly test the collected gas for flammability by holding the burning splint
near the mouth of the second test tube. CAUTION: This gas will make a popping sound.
Light the lab burner. Grasp a small piece of copper foil with your tongs and heat it in the
burner flame until it is red hot. Remove it from the flame and allow it to cool. Scratch the
surface of the metal with a sharp object (such as a scoopula).
Carefully place about one spatula of ammonia carbonate [ (NH4)2CO3 ] into a test tube.
Holding the test tube with a test tube holder, heat the solid gently by holding the test tube
in the flame for a few seconds, then removing it for a few seconds. Continue heating in
this manner for 1 minute. As you heat the solid, carefully waft the air toward your nose to
detect any odor. CAUTION: When heating a test tube, point the open end away from
yourself and anyone nearby. Continuing to heat the solid, place a burning splint at the
mouth of the test tube. Finally, as heating continues, place a piece of blue cobalt paper
just inside the mouth of the test tube. Allow the test tube to cool.
Place approximately 10-15 mL of hydrogen peroxide, H2O2, into a test tube. Have a
wooden splint ready. Add a very small amount (size of a pea) of manganese (IV) oxide,
MnO2, to the hydrogen peroxide. As the reaction occurs, light the splint and allow it to
burn freely for 5 seconds. Blow the flame out and place the glowing splint halfway into
the test tube.
Place a drop of potassium iodide solution, KI, into a small test tube. Add a drop of lead
nitrate solution, Pb(NO3)2. CAUTION: Lead compounds are poisonous, avoid contact.
Dispose of product in beaker under fume hood.
Data Table
Reaction
burning Mg
Mg and HCl
heating Cu
heating (NH4)2CO3
H2O2 and MnO2
KI and Pb(NO3)2
Observations
(predict products from observations)
Analysis
1. Write a balanced equation for each of the reactions performed. Include the physical state
of each substance. (6 pts)
a.
b.
c.
d.
e.
f.
2. Classify each of the reactions as a composition, decomposition, single replacement, or
double replacement. (6 pts)
a.
b.
c.
d.
e.
f.
3. What constitutes a positive test for each of the following gases (3 pts)?
a. Oxygen
b. Hydrogen
c. Water vapor
4. A positive test for hydrogen gas was the “pop” test. What chemical reaction was
occurring? Write a balanced equation representing this reaction. (3 pts)
Hydrogen + ________________ 
_______________
5. For each situation, determine the identity of the gas from the information provided and
write a balanced chemical equation.
a. When potassium bromated (KBrO3) is heated, it decomposes into potassium
bromide (KBr) and a gas that supports the combustion of a glowing splint (2 pts).
i.
ii.
b. Sodium metal reacts violently with water to produce sodium hydroxide (NaOH)
and a gas that “pops” in the presence of a burning splint (2 pts).
i.
ii.
6. Complete a Conclusion paragraph (3 pts).