LAB- CHEMICAL REACTIONS
Purpose: To observe various reactions and to learn how to recognize that a
chemical reaction (chemical change) is taking place.
Equipment: test tubes, test tube rack, 10 mL graduated cylinder, forceps,
pipette, rubber stoppers, and matches
Materials: 18M concentrated sulfuric acid (H2SO4), sodium hydroxide pellets
(NaOH), phenolphthalein solution, solid ammonium chloride (NH4Cl), sodium
iodide solution (NaI), lead nitrate solution (Pb(NO3)2), solid calcium metal (Ca),
water (H2O).
Introduction:
In this experiment you will detect chemical changes by looking for
indications of a chemical reaction. To know for certain that a chemical reaction
has taken place requires evidence that one or more substances have been
changed in identity. Absolute proof of such a change can be provided only by
chemical analysis of the products. However, certain easily observed changes
strongly suggest that a chemical reaction has occurred.
Indicators of a chemical reaction include color changes, temperature
changes, production of gases, and formation of precipitates. Color and
temperature changes are relatively easy to detect. Since many gases are
colorless and odorless, look for bubbling as evidence that a gas has been
produced. A precipitate is an insoluble solid that forms after two solutions have
been mixed. Insoluble means the solid doesn’t dissolve.
Reactions involving temperature changes may be classified as
endothermic or exothermic. Endothermic reactions require or need heat energy
in order to take place. Exothermic reactions release or give off heat energy as
the reaction occurs. The arrows in the diagrams below indicate the direction of
heat flow.
Exothermic Reaction
(System gives off heat to the surroundings)
System
Surroundings
Endothermic Reaction
(System absorbs heat from the surroundings)
System
Surroundings
Caution!!!
Many of the chemicals used in this exercise are very hazardous. Be sure
to read directions carefully and pay close attention to the instructions given by
your lab teacher.
If you spill chemicals on your skin, tell your teacher and immediately
rinse the affected area thoroughly with water.
Strong acids and bases can cause severe burns. On the skin, bases
generally feel slippery to the touch while acids cause a tingling or burning
sensation.
When an acid is diluted in water the evolution of heat may be so great that
the solution splatters or boils over. For this reason, NEVER add water to an
acid. Always remember this rule:
DO AS YOU OUGHT TO, ADD ACID TO WATER!!
Pre-lab Questions:
1. What are the four indicators that allow someone to know that a chemical
reaction has taken place?
______________________________________________________________
______________________________________________________________
2. What will you be looking for to know if a gas has been produced in a chemical
reaction?
______________________________________________________________
______________________________________________________________
3. What is a precipitate?
______________________________________________________________
______________________________________________________________
4. What table can you utilize to help you on determining which product formed in
a double replacement reaction is the precipitate?
______________________________________________________________
Procedure:
Part 1:
A. Use your 10-mL graduated cylinder to measure out 5.0 mL of tap water and
put the water into a clean test tube.
B. Add drops of concentrated sulfuric acid (H2SO4) to the water in the test tube
until a reaction is apparent. Hint: Touch the bottom of the test tube.
1. Record your observation.
___________________________________________________________
2. Is this reaction endothermic or exothermic? ________________________
3. Explain your answer to question #2.
___________________________________________________________
___________________________________________________________
C. Phenolphthalein is an indicator used to detect the presence of acids and
bases. Add 2 or 3 drops of phenolphthalein solution to the test tube
containing the sulfuric acid and water.
4. What color is phenolphthalein in the presence of an acid? ____________
D. Carefully discard the contents of the test tube down the drain with plenty of
running water.
Part 2:
A. Measure 5.0 mL of tap water using a graduated cylinder and pour it into a
clean test tube.
B. Use forceps to count out 8 pellets of sodium hydroxide (NaOH) and add the
pellets to the water in the test tube. Caution: Sodium hydroxide is a strong
base.
C. Stopper and shake the test tube gently until most of the pellets dissolve. Hold
your thumb over the stopper while shaking.
5. Record your observations.
______________________________________________________________
______________________________________________________________
6. Is this reaction endothermic or exothermic? ________________________
7. According to Reference Table I, Heats of Reaction, what is the numerical
value for the dissolving of NaOH in water? ________________________
8. Based on this information, explain the relationship between the sign of the
H value and whether a reaction is endothermic or exothermic.
___________________________________________________________
___________________________________________________________
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D. Add 2 or 3 drops of phenolphthalein solution to the sodium hydroxide and
water in the test tube.
9. What color is phenolphthalein in the presence of a base? _____________
E. Carefully discard the contents of the test tube down the drain with plenty of
running water.
Teacher Verification
Initials: _______ Date: _______
Part 3:
A. Into a clean test tube put about 2 scoops of solid ammonium chloride.
B. Add 5.0 mL of distilled water to the ammonium chloride in the test tube.
C. Stopper and shake the test tube vigorously.
10. Record your observations. Hint: Feel the outside of the test tube.
___________________________________________________________
___________________________________________________________
11. Is this reaction endothermic or exothermic? ________________________
12. Do you predict the H value for this reaction will be positive or negative?
___________________
13. According to Reference Table I, what is the H value for the dissolving
NH4Cl (s) in water? ______________
D. Discard all chemicals down the drain with running water.
Part 4:
A. Pour about 2 mL of lead nitrate (Pb(NO3)2) solution into a clean test tube.
B. Add about 2 mL of sodium iodide (NaI) solution to the lead nitration solution in
the test tube.
C. Allow the test tube to set undisturbed for 5 minutes before you answer the
question below. You can go onto the next step while you wait.
14. What formed during this reaction that indicated a chemical reaction
occurred? _____________________________
15. According to Reference Table F, Solubility Guidelines, identify the name of
the precipitate formed in this reaction. Hint: The word equation for this
reaction is: Lead Nitrate + Sodium Iodide  Lead Iodide + Sodium Nitrate
___________________________
D. Discard all chemicals down the drain with running water.
Part 5:
A. Pour about 5 mL of tap water into a clean test tube.
B. Add 2 or 3 drops of phenolphthalein solution to the water in the test tube.
16. What color is the phenolphthalein in water? ___________________
C. If the phenolphthalein turned pink in the water you must rewash your test tube
and start part 5 over again.
D. The timing of steps E and F are important, so obtain a box of matches
BEFORE you perform step E.
E. Using forceps, drop a small piece of calcium metal (Ca) into the water in the
test tube.
F. After vigorous bubbling action begins, hold a lighted match over the top of the
test tube. Then, extinguish the match by blowing it out and running water on
it. Discard the match in the waste paper bucket after you are sure it is
completely out.
17. What is being formed that causes the bubbling action? ______________
18. What happens when the lighted match is held over the top of the test
tube?
__________________________________________________________
19. Why did the match do this?
___________________________________________________________
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20. Now what is the color of the phenolphthalein in the test tube? __________
21. What does this color indicate?
___________________________________________________________
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G. Discard the contents of the test tube down the drain with running water.
Teacher Verification
Initials: _______ Date: _______
Chemical Reaction Conclusion Questions
1. Why is special care necessary when mixing acids with water?
______________________________________________________________
______________________________________________________________
2. What is the slogan used to help you to remember the correct procedure for
diluting an acid with water?
______________________________________________________________
3. Use Reference Table K, Common Acids, to name and give the chemical
formula of the acid used in this lab.
____________________________________________________________
4. Use Reference Table L, Common Bases, to name and give the chemical
formula of the base used in this lab.
____________________________________________________________
5. Phenolphthalein solution is an indicator used to detect the presence of acids
and bases. According to your data, what is the color of phenolphthalein in:
a) an acid? ____________________
b) a base? __________________
6. According to Reference Table M, Common Acid-Base Indicators, what color
would litmus be in:
a) an acid? ____________________
b) a base? __________________
7. Any chemical spilled on the skin is potentially dangerous. However, acids
and bases pose special problems. Discuss how you might be able to tell
whether a chemical on your skin is an acid or a base.
______________________________________________________________
______________________________________________________________
______________________________________________________________
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8. List the four evidences that indicate a chemical reaction has occurred:
a) ___________________________ b) ___________________________
c) ___________________________ d) ___________________________
9. Use Reference Table I, Heats of Reaction, to answer the following questions
regarding the dissolving of LiBr (s) in water:
a) What is the numerical value of its H? __________________________
b) Is the reaction endothermic or exothermic? ______________________
c) On the diagram below, draw arrows to represent the direction of heat flow
when the solid lithium bromide is dissolved in water.
LiBr
water
d) Compared to the temperature of the water before adding the solid LiBr,
will the solution resulting from the addition of the LiBr feel colder or hotter
in temperature? ____________________________
e) Explain your answer to part d.
___________________________________________________________
___________________________________________________________
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10. In general, if chemicals are mixed in a container, and the container gets
warmer, is the reaction endothermic or exothermic? ________________
11. In general, if chemicals are mixed in a container, and the container gets
colder, is the reaction endothermic or exothermic? ________________
12. Define the term precipitate.
______________________________________________________________
______________________________________________________________
13. When iron (III) chloride solution is added to a solution of sodium hydroxide, a
precipitate forms. This is a double replacement reaction. The general
formula for a double replacement reaction is: AB + CD  AD + BC
a) Using the information given above, complete the word equation for the
chemical reaction:
Iron Chloride + Sodium Hydroxide  _________________ + ________________
b) Use Reference Table F, Solubility Guidelines, to name the precipitate
formed in this reaction. ________________________________