Topic: pH and Indicators
1. List the following as an acid or base
a)
HCl
b) KOH
c) CH3COOH
d)HF
2. Which of the following would have a pH greater than 7
a) HCl
b) CH3OH
c) KOH
d) NaCl
pH scale
power (or potential) of Hydrogen
Ranges from 0-14
measures H+ concentration [H+]
the more H+, the more acidic the solution
Acid, Base, or Neutral
• Neutral solution: pH = 7 [H+] = [OH-]
• Acidic solution: pH LESS THEN 7
H+1 > OH-1
• Basic solution: pH GREATER THEN 7 OH-1 > H+1
How to safely test pH
• NEVER “taste”
• Instruments – use a pH meter
• See if the substance reacts with
a metal other than Cu, Ag, or Au
• Indicators – use a series of
indicators
Indicator
• substance that changes color over narrow pH
range
What color would the following
indicators be in a neutral solution?
yellow
green
colorless
purple
blue
yellow
Use several indicators to narrow
down pH range of substance
Ex: Three samples of the
same solution are tested,
each with a different
indicator. All three
indicators, bromthymol
blue, bromcresol green
and thymol blue, appear
blue
The pH of the solution
must be greater
than_____
Practice using table M
1. What indicator is yellow with a pH 9.8
2. Which indictor is blue with a pH of 5.6
0-3.0Orange3.1.-4.4
Green
Pink
Purple
0-3.7
3.8-5.4
Green
Green
4.5-14
7.7-14
8.4-14
5.5-14
9.7-14