EXPERIMENT 3 – A STUDY OF CHEMICAL CHANGES
INTRODUCTION
Chemistry is a science that investigates changes in matter. Chemical reactions are the changes
chemicals undergo. The changes you can observe are called “macroscopic changes. Often these changes,
such as color changes, the formation of a solid, or the formation of gas bubbles, are visible. Thus, though we
cannot see the atoms and molecules reacting, we can see indications that chemical changes have taken place.
Different atoms and molecules often react in different ways. Chemistry attempts to explain
macroscopic changes in terms of the behavior of atoms and molecules, that is, on the submicroscopic level.
You can use these different reactions to detect the presence of specific kinds of chemicals in mixtures.
PROCEDURE
Obtain an Experimental Page. Place a clear plastic sheet (or plastic wrap) over the Experimental Page. Use the
eye-droppers to put 1 drop of each chemical on the X’s in the indicated spaces on the Experimental Page. For
background contrast, view the drops on the black and white background provided by the X’s. Record the
results for each combination.
QUESTIONS
1. Sodium hydrogen carbonate (sodium bicarbonate) is baking soda, NaHCO3. When HCl is added to
NaHCO3, carbon dioxide bubbles are formed. (a) What is the chemical formula of carbon dioxide? (b)
In what consumer product is the gas commonly found?
2. Which of the other mixings also resulted in the formation of gas bubbles?
3. The body uses hydrochloric acid to help digest food. (a) Where in the body is hydrochloric acid found?
(b) What color does blue food dye turn when HCl is added?
4. Sodium hypochlorite, NaOCl, is a common ingredient in household bleaches and cleansers. What
happens to the color of the blue dye when both HCl and NaOCl are added?
5. Potassium iodide, KI, is the source of iodine in iodized salt. (a) What color is the KI + NaOCl mixture?
(b) What color does starch change to in the presence of KI and NaOCl?
6. A precipitate is a solid that forms upon mixing solutions. (a) Which reaction produced a very bright
yellow precipitate? (b) Which reaction produced a distinctive “muddy” brown precipitate?
7. Review your results and list three different kinds of changes that indicate that a chemical reaction is
occurring.
Experimental Page
Use pipettes to put 1 drop of each chemical on the X’s in the indicated spaces below. For background
contrast, view the drops on the black and white background provided by the X’s. Record the results for each
combination.
a.
b.
c.
d.
e.
f.
g.
X
X
X
X
X
X
X
NaHCO3
+
HCl
h.
HCl
+
Blue dye
i.
Blue dye
+
NaOCl
Now add 1
drop of HCl.
j.
NaOCl
+
KI
Now add 1
drop of
starch.
k.
KI
+
Pb(NO3)2
l.
Pb(NO3)2
+
CaCl2
m.
CaCl2
+
NaHSO4
Be Patient!
Some
chemical
reactions
are slow!
n.
X
X
X
X
X
X
X
NaHSO4
+
Na2CO3
Na2CO3
+
Phenolphthalein
Phenolphthalein
+
NaOH
NaOH
+
AgNO3
AgNO3
+
NH3
NH3
+
CuSO4
CuSO4
+
NaHCO3
Absorb this mixture
onto a white scrap of
paper or tissue and
tape it to your data
table.
EXPERIMENT 3 – A STUDY OF CHEMICAL CHANGES
Date(s) Performed ______________________
Names ______________________________________
Date Due _____________________________
______________________________________
PURPOSE:
RESULTS:
Reaction
Reactants
a.
NaHCO3 + HCl
b.
HCl + blue dye
c.
blue dye + NaOCl + HCl
d.
NaOCl + KI + starch
e.
KI + Pb(NO3)2
f.
Pb(NO3)2 + CaCl2
g.
CaCl2 + NaHSO4
h.
NaHSO4 + Na2CO3
i.
Na2CO3 + phenolphthalein
j.
phenolphthalein + NaOH
k.
NaOH + AgNO3
l.
AgNO3 + NH3
m.
NH3 + CuSO4
n.
CuSO4 + NaHCO3
QUESTIONS
1.
(a)
(b)
2.
3.
(a)
(b)
4.
5.
(a)
(b)
Observation
6.
(a)
(b)
7.
(a)
(b)
(c)