Stuyvesant High School
Department of Biology & Geo-Science
LABORATORY REPORT
EXERCISE #5
ACIDS, BASES and the pH SCALE
Name_____________________________Section__________Teacher________________Date______
PRE-LABORATORY QUESTION – Answer here
I. SUMMARY QUESTIONS
1. Define the following terms:
Acid
Base
Buffer
Indicator
neutralization reaction
2. How do buffers reduce change in the pH of solutions? Why is this important to living organisms?
3. Name a common solution that you predict would be an acid.
II. Data Collection:
I. Determining pH
Box #
Name of test
substance
Color with red
litmus
Color with
blue litmus
pH with
pHydrion
paper
Acid, base, or
neutral?
1
NaOH
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2
HCl
3
3
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Laboratory Manual
Stuyvesant High School
Department of Biology & Geo-Science
5
Box #
Name of test
substance
Color with red
litmus
Color with
blue litmus
pH with
pHydrion
paper
Acid, base, or
neutral?
6
7
8
2. Titration of cabbage juice indicator
Original color of cabbage juice indicator: _______ pH of cabbage juice indicator: ______ (tube C)
Tube
New Color
A
Drops of NaOH
B
Drops of HCl
Drops of HCl needed to
return to original color
Drops of NaOH needed to
return to original color
3. Controlling the pH of a solution
pH of water in tube C__________
pH after adding three drops of
HCL
tube A
Water
pH after adding three drops of
NaOH
tube B
pH of water in tube F__________
pH after adding three drops of
HCL
tube D
Buffer
pH after adding three drops of
NaOH
tube E
4. Optional Exercise - Using an indicator in a biological experiment
Original color of bromthymol blue solution: _________
Tube A
Tube B
Additive
HCl
Color change
Approximate pH
NaOH
Your breath Tube C
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Laboratory Manual
Stuyvesant High School
Department of Biology & Geo-Science
III. Analysis:
1. How can you tell if a solution is acidic, basic or neutral using litmus indicator paper?
2. Which indicator paper gives you a more accurate measure of pH? Explain your answer.
3. Describe the differences in the pH of tubes A and D after adding HCL and the differences in the pH of
tubes B and E after adding NaOH in part III. Give an explanation.
4. What gas are you exhaling into the bromthymol blue solution? How does this gas change the pH of
the bromthymol blue?
5. How does the human brain recognize that CO2 is accumulating in the blood? Use your textbook to
describe the importance of this gas in controlling respiration in human.
Lab Completed ___________________________________________________
Teacher Signature
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Laboratory Manual