Name
Date
Chapter 2
•
Matter and Change
Class
SMALL-SCALE EXPERIMENT
A STUDY OF CHEMICAL CHANGES
Small-Scale Experiment for text Section 2.4
OBJECTIVES



Observe and record chemical changes involving compounds found in consumer products.
Design and carry out experiments to identify compounds in consumer products.
Demonstrate the use of the names and formulas of chemical compounds.
INTRODUCTION
Chemistry is a science that investigates physical and chemical changes in matter. The chemical changes are also
called chemical reactions. Often you can observe some visible changes when a chemical reaction occurs. These
include a change in color, a production of a gas, a formation of a precipitate in a liquid, or the release of energy.
These visible changes are clues to what is happening to atoms within matter at the atomic level.
Chemists explain the changes they observe at the macroscopic level by the changes that occur at the microscopic
level. In fact, explaining changes that are visible by changes that are not visible is fundamental to an understanding of
chemistry.
PURPOSE
In this experiment, you will study some reactions of compounds found in common consumer products. You will
observe and record some visible clues to these chemical reactions. Then you will use chemical reactions to identify
the presence of specific substances in mixtures.
SAFETY




Wear safety goggles, an apron, and gloves when working with corrosive chemicals.
Use full small-scale pipets only for the controlled delivery of liquids.
Don’t chew gum, drink, or eat in the laboratory. Never taste a chemical in the laboratory.
Avoid inhaling substances that can irritate your respiratory system.
Experiment 2 A Study of Chemical Changes
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MATERIALS
Small-scale pipets of the following solutions:
sodium hydrogen carbonate (NaHCO3)
hydrochloric acid (HCl)
FD&C blue No. 1 (blue dye)
sodium hypochlorite (NaClO)
potassium iodide (KI)
starch
lead(II) nitrate (Pb(NO3)2)
calcium chloride (CaCl2)
sodium hydrogen sulfate (NaHSO4)
sodium carbonate (Na2CO3)
phenolphthalein (phen)
sodium hydroxide (NaOH)
silver nitrate (AgNO3)
ammonia (NH3)
copper(II) sulfate (CuSO4)
EQUIPMENT
small-scale reaction surface
empty pipet for stirring
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EXPERIMENTAL PAGE
Use small-scale pipets to put two drops of each chemical on the X’s in the indicated spaces below. For background
contrast, view the drops on both the black and white backgrounds provided by the X’s. Stir each mixture by blowing air
through an empty pipet. For parts c, d, and l, there are additional instructions within the grid. Record what you observe in
Table 2.1.
a.
b.
c.
d.
e.
f.
g.
X
X
X
X
X
X
X
NaHCO3
+
HCl
h.
HCl
+
blue dye
blue dye
+
NaClO
NaClO
+
KI
i.
Now add one drop
of HCl.
Now add one drop
of starch.
k.
KI
+
Pb(NO3)2
l.
Pb(NO3)2
+
CaCl2
CaCl2
+
NaHSO4
j.
m.
Be patient!
Some chemical
reactions are slow!
n.
X
X
X
X
X
X
X
NaHSO4
+
Na2CO3
Na2CO3
+
phen
phen
+
NaOH
NaOH
+
AgNO3
AgNO3
+
NH3
Absorb this mixture
onto a scrap of paper,
expose it to sunlight,
and tape it to your data
table.
NH3
+
CuSO4
CuSO4
+
NaHCO3
Experiment 2 A Study of Chemical Changes
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Place this side of the Experimental Page facedown. Use the
other side under your small-scale reaction surface.
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EXPERIMENTAL DATA
Record your results in Table 2.1 or in a copy of the table in your notebook.
Table 2.1
Experimental Mixings
a.
NaHCO3
+
HCl
b.
HCl
+
blue dye
c.
d.
e.
f.
g.
blue dye
+
NaClO
and then HCl
NaClO
+
KI
and then starch
KI
+
Pb(NO3)2
Pb(NO3)2
+
CaCl2
CaCl2
+
NaHSO4
h.
NaHSO4
+
Na2CO3
i.
Na2CO3
+
phen
j.
phen
+
NaOH
k.
l.
m.
n.
NaOH
+
AgNO3
AgNO3
+
NH3
NH3
+
CuSO4
CuSO4
+
NaHCO3
CLEANING UP
Avoid contamination by cleaning up in a way that protects you and your environment. Carefully clean the small-scale
reaction surface by absorbing the contents onto a paper towel, wipe it with a damp paper towel, and dry it. Dispose of the
paper towels in the waste bin. Wash your hands thoroughly with soap and water.
Experiment 2 A Study of Chemical Changes
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QUESTIONS FOR ANALYSES
Use what you learned in this experiment to answer the following questions.
1. Baking soda is sodium hydrogen carbonate, NaHCO3. When HCl is added to NaHCO3, carbon dioxide bubbles
form. Carbon dioxide contains two atoms of oxygen for every atom of hydrogen. Write the chemical formula for
carbon dioxide. In what consumer product is the gas commonly found?
______________________________________________________________________________
2. In which of the other mixings did bubbles form?
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3. What do you think the gas is that results from the mixing in Question 2?
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4. Cells in your stomach produce hydrochloric acid, HCl, to help digest food. What color does blue food dye turn
when HCl is added?
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5. Sodium hypochlorite, NaClO, is an ingredient in many household bleaches and cleansers. What happened to the
color of blue dye when both HCl and NaClO were added?
_____________________________________________________________________________________________
6. Potassium iodide, KI, is the source of iodine in iodized salt. What color is the KI + NaClO mixture? What color
does starch change to in the presence of KI and NaClO?
_____________________________________________________________________________________________
7. A precipitate is a solid that forms and settles out when some solutions are mixed. Which reaction produced a very
bright-yellow precipitate?
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8. Which other mixings produced precipitates? Describe their colors and appearance with words like milky, cloudy,
and grainy.
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9. Which mixture produced a precipitate that was very slow to form?
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10. Which solutions produced a “muddy” brown precipitate?
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11. Observe the scrap of paper you used to absorb the AgNO 3 + NH3 mixture. What evidence do you see that indicates
that silver compounds are light-sensitive?
_____________________________________________________________________________
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12. Review your results and list at least three different kinds of changes that indicate that a chemical reaction is
occurring.
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13. Describe any other notable observations you made.
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NOW IT’S YOUR TURN!
1. What two compounds turned phenolphthalein pink in the original experiment? Experiment to find out if any other
mixture produces the same result.
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2. What happens when you add ammonia, NH3, to copper(II) sulfate, CuSO4? Does the result depend on the amount of
ammonia you add? Try adding several drops of NH3 to just one drop of CuSO4. Then try adding several additional
drops of CuSO4. Record your observations.
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_____________________________________________________________________________
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3. Sodium hydrogen carbonate, NaHCO3, produces gas bubbles when hydrochloric acid, HCl, is added.
a. Suppose a label of a household product such as baking soda says it contains sodium hydrogen carbonate (also
called bicarbonate of soda). How would you test a sample to indicate the presence of sodium hydrogen carbonate,
NaHCO3?
_____________________________________________________________________________
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b. Try your procedure with some household products whose labels say they contain NaHCO 3. Record your results.
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c. Find out if any of the other chemicals you used in this experiment produce bubbles with hydrochloric acid. Based
on your results, describe any limitations this experiment might have.
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Experiment 2 A Study of Chemical Changes
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4. Many foods contain starches. A starch turns black in the presence of potassium iodide, KI, and sodium hypochlorite,
NaClO. Try adding KI and NaClO to various foods to confirm the presence or absence of starch. Describe what you
do, record what you observe, and explain what you think the results mean.
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______________________________________________________________________________
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5. Potassium iodide, KI, turns black when sodium hypochlorite, NaClO, and a starch are added. The label on a
package of iodized table salt says that it contains potassium iodide, KI. Explain what you could do to confirm this
statement. Try your procedure and record your results. Does your procedure work with noniodized salt? Explain.
______________________________________________________________________________
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6. Many household products, such as dishwasher liquid, contain sodium hypochlorite, NaClO. Design an experiment
to confirm the presence or absence of NaClO in dishwasher liquid and other household chemicals. Add one drop of
starch and one drop of KI to a household product that lists NaClO as an ingredient. A black color confirms the
presence of NaClO. (Note: Do not use full strength household bleach. Your teacher will dilute household bleach
with water.)
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Small-Scale Chemistry Laboratory Manual