Acid/Base pH Lab
• What microorganisms do we study in
microbiology?
• What is one of the ultimate goals of
microbiology?
• So, why do you think we are studying acids
and bases in microbiology?
Acids and Bases
• Acids :
• Have more hydronium ions
• Have a sour taste
• In concentrated forms can be very corrosive
• Example:
• Strong acid – HCl (hydrochloric acid)
• Weak acid – CH3COOH (vinegar)
Acids and Bases
• Bases :
• Have more hydroxide ions
• Have a bitter taste
• Tend to feel slippery because they react with
the oil on our skin to form soap
• Example:
• Strong base – NaOH (sodium hydroxide)
• Weak base – NH4 (ammonia)
Acids and Bases
• pH scale ranges from 0 – 14:
• Solution with a pH of 0 is very acidic
• Solution with a pH of 14 is very basic
• Solution with a pH of 7 is neutral
• pH can be measured with litmus paper or pH
strips
Procedure Part A
• We will be checking the pH of 6 different solutions (there
are 6 stations with 1 solution at each station)
• Before you start, predict what you think the pH of each
solution will be (acidic, basic, neutral)
• Then test each solution with red litmus paper – if it turns
blue, it is a base
• Next test each solution with blue litmus paper – if it turns
red, it is an acid
• If the solution doesn’t change the color of either type of
litmus paper, it is neutral
• Finally, test each solution with a pH test strip – compare
the strip to the box and get a pH reading!
Procedure Part B
• We will now be checking the pH of dilute hydrochloric acid
(HCl), dilute sodium hydroxide (NaOH), and a mixture of
the two – 5 drops of each in test tube (HCl + NaOH = H20 =
NaCl).
• Before you start, predict what you think the pH of each
solution will be (acidic, basic, neutral)
• Then test each solution with red litmus paper – if it turns
blue, it is a base
• Next test each solution with blue litmus paper – if it turns
red, it is an acid
• If the solution doesn’t change the color of either type of
litmus paper, it is neutral
• Finally, test each solution with a pH test strip – compare
the strip to the box and get a pH reading!
Procedure
• Record your results in the data
• Answer all questions completely
• Check your lab report rubric to ensure you are
including everything
• Tape or staple lab sheet into your lab book
• Lab is due tomorrow (10/9/13)