1. Unit 6: Acid-Base Applications Lesson 2: Indicators

2. What Is an Indicator?
An indicator is a weak organic acid or base with different colours for its conjugate acid and base forms.
Example: HIn + H2O In- + H3O+
yellow red
When in highly acidic solutions, an indicator is in its _________ ____ form.
When in highly basic solutions, an indicator is in its _________ ____ form.
10 min

3. Brain Break. Three circles, three related words
Brain Break! Three circles, three related words. Find the missing letter and unscramble the words.
R – solder, brass, bronze

4. Transition Point
An indicator’s transition point is the point at which it is halfway through its colour change, [HIn] = [In-].
At the transition point, the ______ equals the indicator’s Ka value, and hence the ___ equals the indicator’s pKa value.
Note: Since indicators change colour over a range of pH values, we estimate their transition point to be at the midpoint of this range.
10 min

5. Universal Indicator
A universal indicator is a solution that changes colour several times over a range of pH values. It is made up of a mixture of several different indicators.
Example: What colours will appear over a pH range of 3-10 in a universal indicator made up of methyl orange, bromthymol blue, and phenolphthalein?
(See pg. 162) – 10 min

6. Practice:
Pg. 162 #108, 111, 114, 116, and 120
10 min