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CHEMISTRY IH
Lab 2-1 A Study of Chemical Changes
INTRODUCTION: Chemistry is a science that investigates changes in matter. Chemical reactions are
the changes matter undergoes. The changes you can observe are called “macroscopic changes.” Often
these changes, such as color changes, the formation of a solid (precipitation), or the formation of gas
bubbles (effervescence), 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.
In this lab you will study some reactions of common chemicals contained in consumer products. You
will observe the notable macroscopic changes these chemicals undergo. In later labs you will interpret
these macroscopic changes in terms of submicroscopic changes, the behavior of atoms and molecules.
As the name implies, submicroscopic changes are changes we cannot see, even with a microscope. The
essence of understanding chemistry is to infer from macroscopic changes the submicroscopic behavior
of atoms and molecules.
SAFETY:
 Wear your safety glasses.
 Use full small-scale pipettes only for the carefully controlled delivery of liquids.
Materials and Methods:
Small-scale pipettes of the following solutions:
 Sodium hydrogen carbonate (1.00 M NaHCO3)
 FD&C blue No. 1 (blue dye)
 Potassium iodide (0.10 M KI)
 Calcium chloride (0.50 M CaCl2)
 Sodium carbonate (1.00 M Na2CO3)
 Ammonia (1.00 M NH3)
 Hydrochloric acid (1.00 M HCl)
 Sodium hydroxide (1.00 M ? NaOH)
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sodium hypochlorite (1.0% NaClO)
lead(II) nitrate (0.20 M Pb(NO3)2)
sodium hydrogen sulfate (1.00 M NaHSO4)
phenolphthalein (phen)
silver nitrate (0.05 M AgNO3)
20% starch solution
copper (II) sulfate
2 eight – well reaction strips
Use small-scale pipettes to put 2 drops of each chemical into separate spots on the reaction strip. Be sure to
know which spot has which reactants. For background contrast view the substances on both black and white
backgrounds. Stir each mixture with a separate toothpick.
A. NaHCO3 + HCl
D. KI + Pb(NO3)2
G. NaHSO4 + Na2CO3
J. phen + NaOH
M. NH3 + CuSO4
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B.
E.
H.
K.
N.
HCl + blue dye
Pb(NO3)2 + CaCl2
Na2CO3 + phen
NaOH + AgNO3
CuSO4 + NaHCO3
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C. blue dye + NaClO, then add 1 drop HCl
F. NaClO + KI, then add 1 drop of starch
I. CaCl2 + NaHSO4, be patient
L.AgNO3+NH3, absorb on paper,hold to light
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RECORDING YOUR OBSERVATIONS
On a separate sheet of paper, create a data table and record what you see on the table, then answer the
questions below using complete sentences.
Questions
1. Sodium hydrogen carbonate is baking soda (NaHCO3). When HCl is added to NaHCO3, carbon dioxide
bubbles are formed. What is the chemical formula for carbon dioxide? In what consumer product is the
gas commonly found?
2. Which of the other mixings effervesce?
3. What do you think the gas is that results from the mixing in Question 2?
4. The body uses hydrochloric acid, HCl, to digest food. Where in the body is the hydrochloric acid found?
What color does blue food dye turn when HCl is present?
5. Sodium hypochlorite, NaClO, is a common ingredient in household bleaches and cleansers. What
happened to the color of the blue dye when both HCl and NaClO are 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 separates upon mixing solutions. Which reaction produced a very bright
yellow precipitate?
8. Which other mixings produces precipitates? Describe their colors and textures with words like milky,
cloudy, and grainy.
9. Which mixture produced a precipitate that was slow to form?
10. Which solutions produced a distinctive “muddy” brown precipitate?
11. Observe the scrap of paper you used to absorb the AgNO3 + NH3 mixture. What evidence do you see
that indicates that silver compounds are light sensitive?
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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