Equation Writing and Predicting Products
Chemistry I Acc
Introduction:
If you examine your bicycle after it has been left out in the rain a number of times you will find
that it has begun to rust. Rust is a slow chemical reaction of the iron in the bicycle with oxygen. If a
piece of sodium is put in 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 clear and simple. 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, 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 and balance chemical equations to
describe the reactions.
Materials
goggles
magnesium ribbon
triangular file
copper strip
cobalt chloride paper
lab burner
watch glass
glycerin
bent glass tube
test tube tongs
manganese(IV) oxide (MnO2)
lead(II) nitrate (Pb(NO3) 2) 0.1M
limewater (Ca(OH)2 solution)
ammonium carbonate ((NH4)2CO3)
crucible tongs
6 test tubes
wooden splints
rubber tubing
graduated cylinder
potassium iodide (KI) 0.1M
copper(II) carbonate (CuCO3)
one-hole rubber stopper
hydrogen peroxide (H2O2) 10% solution
Safety Warnings
Wear your goggles at all times during this investigation. Avoid looking directly at the burning
Magnesium. The bright light could seriously damage your eyes. Tie back loose hair. Hydrochloric acid
is corrosive. Avoid direct contact with it. If you get some on your skin, immediately wash it off with
copious amounts of water. Ammonia is a skin and respiratory irritant so avoid inhaling it deeply. Lead
compounds are poisonous so be sure to avoid contact with skin. If contact occurs immediately wash it
off with copious amounts of water and inform your teacher. Glass tubing breaks easily. Exercise
caution when working with it and use glycerin.
Procedure:
1. Put on your goggles and wear them throughout the lab. For each of the reactions, record your
observations in the data table. Observations should include any evidence that a chemical reaction has
taken place; the results of any test performed on any gases produced; the appearance of the
products; and any other relevant data.
2. Obtain a 2 cm long piece of Mg ribbon. This length is approximate. The exact size is not important.
Holding the Mg ribbon with the crucible tongs, carefully light the ribbon with the lab burner. Once
lit hold the Mg ribbon over a watch glass to collect any ash and debris. When the Mg is done
burning turn off the burner. CAUTION: Make sure hair is tied back. The tongs will be hot even
after the Mg has finished burning. Do not touch them for at least five minutes. Place them on the
watch glass to cool. Do not look directly at the Mg while it burns.
3. Read steps 3 and 4 completely before starting step 3.
Place a medium test tube in a test-tube rack. Have a
second test tube of the same size ready in a pair of
test-tube tongs. Add 2 fingers worth of 3.0M
hydrochloric acid (HCl) to the first test tube. Drop a
2-cm piece of Mg into the acid. Again, the length is
approximate. The exact size is not important.
CAUTION: Hydrochloric acid is corrosive. Avoid
spills and splashes. If you do spill acid immediately
rinse the area with plenty of water and notify your
teacher.
4. 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 test tube and
inserting the burning splint into the mouth of test
tube #2. CAUTION: The gas in the test tube will
make a LOUD popping sound, do not be startled.
5. Obtain a copper strip. Scratch it with the triangular file. Light the lab burner. Grasp the piece of
copper with the crucible tongs and heat it in the burner until it blackens. Remove from the flame and
allow it to cool. Try now to scratch the blackened part with the file.
6. Carefully place about one heaping spatula in of ammonium carbonate ((NH4)2CO3) in a medium test
tube. CAUTION: The odor produced in this reaction is quite noxious. Make sure to only waft and
not inhale directly. The gas coming from the tube is a respiratory and skin irritant, so avoid inhaling
it deeply. Hold the test tube with test tube tongs and slowly heat the test tube by placing it in the
flame for a few seconds and then removing it for a few seconds. Continue heating in this manner for
a total of about 1 minute. As you heat the solid carefully waft the air towards your nose to detect any
odor. CAUTION: When heating the test tube, make sure the open end points away from any person.
After you have detected the odor continue to heat the test tube in the fume hood. Place a burning
wooden splint in the mouth of the test. Finally, as the heating continues, place a piece of Cobalt
chloride paper just inside the mouth of the test tube. Put the test tube in the rack to cool. Turn the
burner off.
7. Place approximately two fingers of 10% hydrogen peroxide (H2O2) into a medium test tube. Add a
small amount of (about the tip of a spatula or wooden splint) of Manganese(IV) oxide (MnO2) to the
hydrogen peroxide. Then wait ten minutes. Light a wooden split and allow it to burn for a few
seconds. Then blow out the flame and quickly place the glowing embers halfway into the test tube to
see if they relight. Do not stick the splint in the liquid.
8. Place two drops of potassium iodide solution, KI, into a small test tube. Add two drops of lead nitrate
solution, Pb(NO3 )2 . CAUTION: Lead compounds are poisonous so be sure to avoid contact with
the skin. If contact occurs, immediately wash the area with plenty of water and inform the teacher.
Clean up all spills immediately.
9. Assemble the one-hole stopper, with the glass elbow in the stopper
and attach the rubber tubing to the glass tube. CAUTION: Glass
tubing breaks easily. Exercise caution when working with it. Use
glycerin as a lubricant. Place one heaping spatula of copper
carbonate CuCO3 in an extra large test tube. Prepare a second
medium sized test tube with three to four fingers of limewater.
Light the lab burner. Holding the test tube containing the Copper
carbonate with the test tube tongs, heat the copper carbonate. As the
copper carbonate is heated place the rubber tubing into the test tube
with the limewater. The open end of the rubber tubing must be
submerged in the limewater so the gas produced by heating the
copper carbonate can bubble through the limewater. Record any
change you observe with the copper carbonate or the limewater.
10. Clean up your work area and wash your hands before leaving the laboratory.
Chemistry I Acc
Name______________
Equation Writing and Predicting Products
Pre-Lab
Read the entire laboratory assignment and the relevant pages in your textbook. Answer all pre-lab
question before beginning the lab.
1. What constitutes a positive test for each of the following gases?
a. oxygen __________________________________________________________________
b. hydrogen ________________________________________________________________
c. carbon dioxide ____________________________________________________________
d. water vapor ______________________________________________________________
e. ammonia ________________________________________________________________
2. What is the proper way to small a substance in the lab? Why should care be taken when smelling a
gas such as ammonia?
3. What is the role of a catalyst in a reaction? How can you tell when a substance serves as a catalyst?
4. One way to identify limestone (Calcium carbonate - CaCO3) is to drop a small amount of
hydrochloric acid on it. A positive test results in a fizz of carbon dioxide being produced. Predict
the other two products and balance the equation.
Data and Observations
Data Table 1
Reaction
burning of Mg
Mg and HCl
Write observations of reaction here
Reaction
Write observations of reaction here
Burning Cu
Heating Ammonium
Carbonate
Hydrogen peroxide
plus the catalyst
manganese dioxide
KI and Pb(NO3)2
Heating Copper
Carbonate
Analysis and Synthesis
1. Write a balanced equation for each reaction performed. Include the physical state of each substance.
a. ________________________________________________________________________
b. ________________________________________________________________________
c. ________________________________________________________________________
d. ________________________________________________________________________
e. ________________________________________________________________________
f._________________________________________________________________________
g. ________________________________________________________________________
2. Classify each of the reactions as direct combination, decomposition, single replacement or double
replacement.
a. _________________________________ b. ___________________________________
c. _________________________________ d. ___________________________________
e. _________________________________ f. ____________________________________
g. _________________________________
3. Limewater is an aqueous solution of Ca(OH)2. What is the cloudy white precipitate that forms with
carbon dioxide gas. Write a balanced chemical equation for this reaction.
4. A positive test for hydrogen was the ”pop” test. What category of chemical reaction was occurring?
Write a balanced chemical equation to represent this reaction.
5. For each of the following situations, determine the identity of the gas produced from the information
given and write a balanced chemical equation that represents the reaction.
a. When potassium bromate (KBrO3) is heated it decomposes into potassium bromide and a gas that
reignites a glowing splint.
b. Sodium metal reacts violently with water to produce sodium hydroxide and a gas that “pops” in
the presence of a burning splint.
c. The recipe for the volcanic eruption used in many science projects is the reaction of baking soda
(NaHCO3) and vinegar (CH3COOH). When these compounds are mixed together, the salt
sodium acetate (NaCH3COO) is formed as well as a gas that extinguishes a burning flame and
also a liquid substance that turns cobalt chloride paper from blue to pink.
6. Cobalt chloride paper is a hydrated salt used for making humidity gauges. The formula of the
hydrated form is CoCl2•2H2O. What color is associated with the hydrated form of cobalt chloride?
How might is be to predict weather changes?
7. Manganese dioxide is considered to be a catalyst in the decomposition of hydrogen peroxide. Design
an experiment in general terms to show that manganese dioxide is a catalyst.