Lab - Types of Chemical Reactions 4352 (35 points)
Introduction
There are many kinds of chemical reactions and several ways to classify them. One
useful method classifies reactions into four major types. These are (1) direct combination,
or synthesis; (2) decomposition, or analysis; (3) single replacement; and (4) exchange of
ions, or double replacement. Not all reactions can be put into one of these categories. Many,
however, can.
In a synthesis reaction, two or more substances (elements or compounds) combine to form
a more complex substance. Equations for synthesis reactions have the general form
A + B → AB. For example, the formation of water from hydrogen and oxygen is written
2H2 + O2 → 2H2O.
A decomposition reaction is the opposite of a synthesis reaction. In decomposition,
a compound breaks down into two or more simpler substances (elements or compounds).
Equations for decomposition reactions have the form 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 (an element). Equations for single replacement reactions have two
general forms. In reactions in which one metal replaces another metal, the general
equations is X + YB → XB + Y. In those in which one nonmetal replaces another nonmetal,
the general form is X + AY → AX + Y. The following equations illustrate these types of
reactions:
Zinc metal replaces copper(II) ion:
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
Chlorine (a nonmetal) replaces bromide ions:
Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(l)
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 form AB + CD → AD + CB. Most replacement reactions, both single and
double, take place in aqueous solutions containing free ions. In a double replacement
reaction, one of the products is a precipitate, an insoluble gas, or water. An example is the
reaction between silver nitrate and sodium chloride in which the precipitate silver chloride
is formed:
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
All of the types of reactions discussed here may be represented by balanced
molecular equations. Reactions involving ion exchanges may be represented by ionic
equations also. In this investigation you will be concerned only with molecular 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 and the subscript of an
element must yield the same result on both sides of the balanced equation.
In this investigation you will observe examples of the four types of reaction
described above. You will be expected to balance the equations representing the observed
reactions.
Purposes
Perform and observe some chemical reactions.
Identify reactants and products of those reactions.
Perform tests on the products. Classify the reactions and write balanced equations.
Pre-lab
1. Read the entire lab.
2. Summarize the procedure in your lab notebook.
3. Answer the pre-lab questions.
4. Tables are NOT needed. Allow a full page for each part of the procedure in which you
will record observations and answer analysis question #1.
Observations:
Recording of ALL observations is a VERY important in this lab.
You MUST Write VERY descriptive, and detailed, observations of the
“before”, “during”, and “after” the reaction for all reactants and products.
Record all: color change, gas release, heat exchange, appearance, and
precipitate formation, phase change, etc…
Pre-lab Questions:
1. Search the “Chemical Database” link and describe the dangers of exposure to
Sulfuric acid and barium hydroxide. (Contact with skin, eyes, inhalation, and ingestion)
2. How would you be able to tell whether an exothermic or endothermic reaction occurred?
Equipment
Bunsen Burner
Wood splints
Crucible tongs
Spatulas
Watch glass
Materials
Zinc, mossy (Zn)
0.1 M potassium chromate
0.05 M barium nitrate
Sodium bicarbonate
6 M hydrochloric acid (HCl)
Zinc ribbon
0.5 M sulfuric acid
Safety
Large test tubes (7)
Test tube holders
Test tube racks
10 mL graduated cylinders
1 M copper(II) sulfate
Magnesium ribbon (Mg)
Copper(II) carbonate
Limewater
pH paper
0.01 M barium hydroxide
phenolphthalein
Handle the chemical and hot glassware with care to avoid burns and
breakage. You MUST wear goggles!
Procedure
Part A
Place a watch glass near the base of the burner. Examine a piece of magnesium ribbon.
Record your observations. Using crucible 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 WATCH GLASS. When
the ribbon stops burning, put the remains in the watch glass. Examine this product.
Record your observations. Dispose of the metal in the trash and wash the watch glass.
Part B
Place two small scoops of copper(II) carbonate in a clean, dry test tube. Note the
appearance of the sample. Record your observations.
Using a test tube holder, heat the copper (II) carbonate strongly for about 2 minutes.
Make sure to follow proper heating procedure. Insert a burning wood splint into the test
tube. What happened to the flame? Note any change in the appearance of the residue in the
test tube. Record your observations.
Part C
Place 2 large scoops of sodium bicarbonate in a clean dry test tube. Note the appearance of the
sample. Record your observations. Fit the test tube with a one-hole stopper and delivery tube.
Obtain the limewater bottle. DO NOT SHAKE! Fill a third of second test tube with limewater,
(the saturated solution of calcium hydroxide). Check the pH of the limewater. Record.
Place the end of the delivery tube in the limewater. Heat the sodium bicarbonate for 1-2 min
and observe the limewater. Discontinue the heat and remove the delivery tube from the
limewater. Check the pH of the solution produced in the test tube. Let the test tube stand
undisturbed for 10 minutes. Make observations of both tests tubes. Record.
Part D
Stand a clean, dry test tube in the test tube rack. Fill about a quarter of a test tube with
6 M hydrochloric acid. CAUTION!!! Handle acids with care. Carefully add a scoop of zinc
metal into the acid in the test tube.
Using a test tube holder, invert a second test tube over the mouth of the test tube in which
the reaction is taking place. See Figure below. Remove the inverted tube after about 1min,
keep it inverted, and quickly insert a burning wood splint into the mouth of the tube. Note
the appearance and temperature of the substance in the reaction test tube. Record
observations.
Part E
Add about 5-10 mL of 1 M copper(II) sulfate solution to a clean, dry test tube. Place three
pieces of zinc ribbon in the solution. Leave the test tube in the test tube rack and make
observations about 40 minutes later. Decant the solution into a small beaker. Record the
appearance of the solution and the zinc before and after the reaction.
Part F
Add about 5-10 mL of 0.1 M potassium chromate to a clean, dry test tube. Next, add about
5-10 mL of 0.05 M barium nitrate solution to the test tube. Let the solution rest for 20
minutes and record your observations.
Part G
Place approximately 3 mL of 0.01 M barium hydroxide solution in a test tube and add one
drop of phenolphthalein. Using a medicine dropper, add 0.5 M sulfuric acid one drop at a
time until the color just disappears. Let the test tube stand undisturbed for 10 minutes.
Note the appearance of the contents of the test tube.
Analysis Questions
1. a) As a class, we will write a balanced chemical equation(s) for each part in this
experiment. (Some parts have more than one). We will include the phase of each
reactant and product. (s, l, g, aq)
b) Use the heat symbol, ∆, above the yield arrow to indicate that heat was needed
to obtain the products.
c) Write the names of the reactant(s) and product(s) below the molecular
equation for each reaction.
d) Indicate the type of reaction that took place.
2. In this experiment, which tests were used for the presence of CO2 gas?
3. Explain why did the reaction in part D occur? Would the reaction in the opposite direction
occur?
4. What is the aqueous salt in part D? How would you retrieve it?
5. Why was the test tube in part D, kept inverted while testing for the presence of hydrogen
gas?
6. List five different evidences you have observed that indicated that a chemical reaction
occurred. (Give the procedure part for each)
7. Which reactions were exothermic? Which endothermic?
8. Explain why the pH in part C became more acidic. (Hint: What is the product of a
reaction between carbon dioxide and water?)
Conclusion
Write a short conclusion paragraph.
(Experimental errors are not required)
Part A
Watch glass
Bunsen burner
Striker
A piece of magnesium ribbon
Crucible tongs
Part B
Copper (II) carbonate
Scoopula
Test tube
A test tube holder
Wood splint
Matches
Bunsen burner
Striker
Part C
Scoopula
Sodium bicarbonate
2 test tubes
A one-hole stopper and delivery tube
10 mL graduated cylinder
Limewater
pH paper
Bunsen burner
Striker
Test tube clamp
Part D
2-test tube
Test tube rack
10 mL graduated cylinder
6 M hydrochloric acid. CAUTION!!
Zinc metal
A test tube holder
Wood splint
Matches
Part E
10 mL graduated cylinder
1 M copper (II) sulfate solution
 Zinc ribbon
2 Test tube
Glass Stirring rod
Test tube rack
Part F
2-10 mL graduated cylinder
0. 1M potassium chromate
Test tube
0.05 M barium nitrate
Test tube rack
Part G
10 mL graduated cylinder
0.01 M barium hydroxide
A test tube
Phenolphthalein
A medicine dropper
0.5 M sulfuric acid CAUTION!!
Part C
Scoopula
Sodium bicarbonate
2 test tubes
A one-hole stopper and delivery tube
10 mL graduated cylinder
Limewater
pH paper
Bunsen burner
Striker
Test tube clamp