Types of Chemical Reactions 1

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					Types of Reactions Lab     v7       Dr. Breinan        Chemistry        p.1

                                  Types of Chemical Reactions
Introduction: There are many kinds of chemical reactions and many ways of classifying them.
Most of the reactions talked about in a first year chemistry course can be classified as one of five
major types of reactions. These reactions are: synthesis (sometimes called combination);
decomposition (sometimes called “analysis” if elements result); single replacement; double
replacement, and combustion. These five types of reactions are summarized below. Consult your
class notes and text for more information.
        Remember, though, that not all chemical reactions can be put into one of these categories.
For example, a major group of compounds that undergo other types of reactions is the “organic”
compounds (compounds consisting mainly of carbon and hydrogen). While there are many other
organic reactions, most undergo combustions. Our study of organic reactions will be limited to
combustion reactions.
        In a synthesis reaction, a single product (a compound) is formed from two or more simple
substances (elements or simple compounds). An example of such a reaction is the formation of
water from its elements: 2 H2 + O2 --> 2 H2O.
       A decomposition reaction is exactly the opposite of a combination reaction. A single
reactant compound breaks down into two or more simpler substances (elements or simpler
compounds). The breakdown of a chlorate into oxygen and a chloride salt is one example:
2 NaClO3 ---> 2 NaCl + 3 O2.
        In a single replacement reaction, an element (alone in its elemental form) replaces a similar
element in a compound. The result is a new element and a new compound. The replacement only
occurs if the element that does the replacing is “more active” than the element that gets replaced.
Equations for single replacement reactions have two general forms depending on the types of
elements involved. In general, metal elements can replace other metals or hydrogen in compounds.
Halogen elements may replace other halogens in compounds. These replacements almost always
occur in solutions, i.e. the initial compound is dissolved in water. In addition, the compounds are
made of ions, i.e. ionic compounds or acids. Usually the new compound made as a product stays
dissolved in solution (see examples below), however, sometimes it may form a solid. When the
elements are alone they are simply atoms (metals, usually solids) or diatomic molecules (for
halogens or hydrogen... they may be gas- H2, F2, or Cl2, liquid- Br2 or solid- I2). We will learn later
that these reactions are also examples of “redox” reactions.
Metal/hydrogen replacements look like: A + BX --> AX + B (A & B = metals or H, X = anion).
(Note: subscripts are not shown in this general type of representation because they may vary)
 ex: Aluminum replaces copper (ions): Al (s) + Cu(NO3)2 (aq) --> Al(NO3)3 (aq) + Cu (s)
For nonmetal replacements, the form is X2 + AY --> AX + Y2. (X & Y = halogens, A = cation).
 ex: Chlorine replaces bromine (ions): Cl2 (g) + 2 KBr (aq) --> 2 KCl (aq) + Br2 (l)

        Double replacement reactions occur between two compounds which are either ionic or acids.
The cations of two compounds switch places. For this type of reaction, acids are thought of as made
of hydrogen ions and an anion. The cations can be thought of as “replacing one another.” This type
of reaction also nearly always occurs in solution and can be represented by AX + BY --> AY + BX
(A and B are cations, X and Y are anions). In a double replacement reaction, one of the products
formed is a precipitate (s), an insoluble gas (g), or water (l). Normally the other product stays
dissolved in solution.
       In a combustion reaction a chemical reacts with oxygen producing oxides and lots of energy,
normally in the form of heat and/or light. Some synthesis reactions (like the example above that you
Types of Reactions Lab       v7       Dr. Breinan         Chemistry         p.2

will witness in this lab) can be considered combustions if they involve oxygen and occur rapidly
enough for a noticeable release of energy. We will be mostly concerned with organic combustion of
hydrocarbons (chemicals made up mostly of hydrogen and carbon atoms, but often including oxygen
atoms as well). Organic combustions are commonly used to produce heat and always produce
carbon dioxide and water as products. This can be represented symbolically as follows (x, y, and z
are the number of atoms of C, H, and O in the hydrocarbon molecule):
                  Combustion:                 CXHYOZ + O2           --> CO2       +    H2 O
       In this experiment you will observe examples of all five types of chemical reactions described here
and observe the phases of the chemicals involved. Here are some hints for determining what phase
chemicals are in: Hint 1: The phases of most elements are obvious from looking on your periodic
table. Since most pure elements cannot dissolve in water, their phase is usually the same whether
the reaction occurs in solution or not. Hint 2: You cannot tell whether a chemical is a pure liquid or
dissolved in water just by looking at it. But, any chemical with a “percent, %” or “molarity, M” rating, such
as “1 M” or “10%”, is dissolved in water. The molarity or percent is used to tell you the concentration of
the solution (how much chemical in how much water) and will be studied later in the year. Hint 3: common
sense tells you that ionic chemicals cannot be liquid at room temperature! Hint 4: You may have to make
an educated guess for some of the products.

The burning splint test for three common gases:
You will also perform the three splint tests for gases. The tests are performed by placing burning or
 glowing wood splints into a test tube where the gases may be present; the results will differ based
 on the gas present as described here:
gas          test and result
CO2 a burning splint is put out
H2 a burning splint causes a small explosion (a loud “pop” or “SQWARK”) in forming water
O2 a burning splint burns more brightly; a glowing splint bursts into flame (maybe making a soft “pop”)
- To observe some chemical reactions and identify reactants and products of those reactions.
- To classify reactions as to type and write symbols showing phases.
- To practice and learn the splint test for gases.

SAFETY: Wear goggles, gloves, and aprons when working with chemicals. Read safety notes for
 each experiment before performing it!

gas burner apparatus  test tube rack      4 test tubes (save 2 dry tubes for reactions 3 and 5)
  test tube holder metal tongs       wood splint        steel wool        various chemicals

1) Lab procedures handout: describe the proper use of a test tube holder, especially heating over a flame.
  Which reactions in this lab will you use the holder for?
2) (a) What does (aq) mean? (b) How can you tell by looking at a chemical whether it is a pure liquid or
  simply a chemical dissolved in water? (c) What can you do in this lab to help you decide?
3) What is done to perform the flaming wood splint test for gases? What three common gases can be
  distinguished by this test?
4) Design a data table to record observations of each reaction. First you will describe the appearance of the
  unreacted chemicals. You will then record the evidence of the reaction that occurs. These observations
  should help you fill in the phases of the chemicals in the assignment. You need only take brief
  observations in this lab (3 words maximum for each!)
Types of Reactions Lab     v7       Dr. Breinan        Chemistry        p.3

Procedure: Once you have taken or mixed chemicals at the dispensing area, move away to allow
others to access them.
**SAFETY Always be careful with the burner set up. Use only a low flame for this lab. **
** Make sure you replace droppers back in the containers they came from! **

Double Replacement reactions:
1. Add about 5 mL of 0.5 M sodium carbonate solution, Na2CO3 to a test tube. To this solution, add
  about 1 mL of 6 M HCl. **SAFETY Handle acids with care! Severe burns and tissue damage
  can result. ** Record the evidence of the reaction.
Disposal: Put the acid in the acid neutralizer

2. Add up to 2 mL of 0.1 M zinc acetate, Zn(C2H3O2)2 to a test tube. Add one dropperful of 0.1 M
  sodium phosphate (Na3PO4) solution to the same test tube. Record the evidence of the reaction.
Disposal: Wash down the sink with running water.

Decomposition reactions:
3. Add copper (II) carbonate to fill a dry test tube just above the rounded portion at the bottom. Use
a test tube holder to heat the test tube over a low burner flame. This is the ONLY station that you
should use the holder for! **SAFETY
 - Hold the test tube holder so you will not accidentally squeeze it open and drop the tube.
  - Hold the tube at an angle so your hand is not directly over the flame
  - Move the tube slowly back and forth through the flame**
Observe the evidence of chemical change. Also, see if you can see the solid melting.
After about 30 seconds have your partner light a wood splint. Away from the flame, put the splint
into the mouth of the tube (make sure the entire flame goes into the tube but do NOT drop the splint
into the tube!) Observe the result of the flaming splint test. Record the result of the splint test and
the changes in the chemical.              DO NOT PLACE THE HOT TEST TUBE in a plastic test
tube rack… let it cool a few minutes first! The holder will prevent it from rolling off the counter.
Disposal:     Dry chemical: dump in waste beaker.           Splint: save for reactions 4 and 6.

4. One partner should light and attend to the flame (keep the flame fairly low), and be responsible
for all actions with the splint. The other partner is responsible for the test tube and chemical. This
partner should first obtain the chemicals by adding one to two inches of 3% hydrogen peroxide
(H2O2) to a test tube and then adding a medium scoop of potassium iodide. The reaction will begin
in a few seconds, but continue for at least 2 minutes, so there is plenty of time to return to your
station for the rest of the test.  SAFETY: the flame at this station is ONLY for lighting the splint!
Do NOT heat the test tube!
At your station: (record observations only after all steps completed)
    - Hold the test tube in your hands and gently shake it once. Briefly observe the evidence of
         chemical reaction
    - Light the splint for 5 seconds, then blow it out lightly so that the tip glows, but is not aflame
    - Mix the contents of the tube for 5 seconds, then immediately place the glowing splint in the
         tube (down to just above the liquid if necessary) and observe the result of the splint test for
         the gaseous product. DON’T DUNK THE SPLINT IN THE LIQUID!
Record the result of the splint test and the changes in the chemical.
Disposal:     Test tube: dispose in your sink.       Splint: save for reactions 3 and 6.
Types of Reactions Lab     v7       Dr. Breinan          Chemistry         p.4

Single Replacement reactions:
5. Add about 2 mL of 1 M copper (II) sulfate solution, CuSO4 to a test tube. Drop a small piece of
  zinc into the solution. Look for an initial reaction, then allow the reaction to occur while
  performing other experiments. When you finish your other work, describe the changes in the
  solution and the zinc.
Disposal:     Both the solution and the zinc go in the appropriate waste container (use excess water
  to wash the zinc out if necessary).
                                                                           Keep away from the flame!
6. Add about 2 mL of 6 M HCl to a test tube. Read ahead...              collection step        test step
  make sure you are prepared for all remaining instructions
  before starting the reaction.   SQWARK alert!!
- Have your burner lit with a low flame (SAFETY: ONLY for
  lighting a wood splint-- do NOT heat the test tube!.)
- Place a 2-3 cm strip of magnesium in the test tube with the
                                                                     reaction tube
- Immediately, with your hands (not a test tube holder), and
   well away from the burner, hold a dry test tube upside
   down tightly over the reacting tube to collect the gas
   produced (see collection step in diagram to the right).                                      flaming
   Observe the evidence of reaction while proceeding.                                           splint
- After about 15-20 seconds, light a wood splint and move it away from the burner to where you have
   the tubes. In one motion at the same time, do the following three things (see in the diagram):
   move the tube with the collected gas slightly away from the acid, tilting it very .slightly away from
   you as you bring the lighted splint to the opening of the collection tube. (Do NOT hold the splint
   over the test tube with the acid!!) **SAFETY Be prepared for a noise so you do not drop the
   tube!! **
- Record your observation and refer to the splint test. Be sure to observe the contents in the reaction
  tube as well.
Disposal:     Acid: neutralize in the acid neutralizer
              Splint: save for reactions 3 and 4.

7. Use a clean piece of copper wire, or use steel wool to clean one until shiny. Note its appearance.
Move the wire through the hottest part of the burner flame for about 30 sec. Note the change in
appearance in the wire. Clean and return the wire to your teacher.

8. **SAFETY Do not look directly at burning magnesium... eye damage could result!! **
Hold a 2-3 cm strip of magnesium in metal tipped tongs. Examine the magnesium and record its
appearance. Light the burner and hold the magnesium in the flame until it begins to burn. LOOK
AWAY IMMEDIATELY AS IT BURNS! Examine and describe the product. Let the product cool
and dispose of it in the trash.

**FINAL Clean-up! Be sure to brush your test tubes inside and out when done, especially the
  tube that was used for copper (II) carbonate! **
When all done with the splint, make sure it is doused in water and throw it in the trash.
     Types of Reactions Lab          v7         Dr. Breinan            Chemistry         p.5

Assignment Sheet- tear off this page!             Note: balancing is NOT needed on this lab.
     1. Hand in a) pre-lab, b) your final data table with observations c) this detached sheet (must be in this
         order and with nothing else!) All write-up answers should appear on this page!
     2. The chemical or word equation for the reactions you performed is written below.
     (a) Write the chemical formulas under the names of the chemicals or write the names of the chemicals under
         the formulas.
     (b) next to each chemical formula in all rxns write in (s), (l), (g), or (aq) to indicate the phase

     Double Replacement reactions: (the first reaction also includes a decomposition)
Rxn 1      Na2CO3               +         HCl          --->          NaCl        +        H2O        +           CO2

Rxn 2        zinc acetate       +   sodium phosphate --->             zinc phosphate      +     sodium acetate

    Decomposition reactions                            
Rxn 3            copper (II) carbonate             --->         copper (II) oxide +        carbon dioxide

Rxn 4                 H2O2             ---->               O2                +           H2O

     Single Replacement reactions:
Rxn 5          Zn       +                 CuSO4            ---->        Cu           +     ZnSO4

Rxn 6      magnesium            +   hydrochloric acid         --->      magnesium chloride       +       hydrogen

     Synthesis reactions
Rxn 7           Cu          +         O2        --->            CuO

 Rxn 8      magnesium           +    oxygen       --->        magnesium oxide
Types of Reactions Lab      v7         Dr. Breinan        Chemistry       p.6

3. In the Rxns above, which specific chemical(s) in which Rxns could also have the symbol 

4. This experiment involved the combustion of methane, CH4. Describe where this was found in
   the experiment. Also write the chemical equation for this combustion.

5a. Why did the flame go out in reaction 3? b) Why did the splint light on fire in reaction 4?

6. PRACTICE: Identify the type of each of the following reactions. Answer here 

a.   2 AgNO3 (aq) +       Cu (s) -->        Cu(NO3)2 (aq) +        2 Ag (s)
b.     BaCl2 (aq) +       Na2SO4 (aq) -->       BaSO4 (s) +      2 NaCl (aq)
c.     Cl2 (g) +    2 NaBr (aq) -->       2 NaCl (aq) +      Br2 (l)
d.   C2H6O (l) + 3 O2 (g) --->         3 H2O (g) +     2 CO2 (g)
e.   2 KClO3 (s) --->     2 KCl (s) +       3 O2 (g)
f.    AlCl3 (aq) + 3 NH4OH (aq) --> 3 NH4Cl (aq) +                 Al(OH)3 (s)
g.   2 H2 (g) +     O2 (g) -->    2 H2O (l)

7 (a) Write the chemical formulas for all of the precipitates in reactions 6a to g above.

(b) List an alternate phase symbol that
    could be used for the precipitates:

(c) Which reaction (6a-g) describes the process
of the flaming splint test that resulted in a “sqwark”?
(NOT the reaction that produces the gas)

Extra credit. There exists another common method for testing for the presence of carbon dioxide
gas. Research and write a balanced reaction using as many symbols as you can for this method. Be
sure to identify your source!

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