2. Acid-base indicators An acid base indicator is a special substance that exists in two forms ( colours) depending on it’s pH level. We have already talked about one of the most common indicators litmus (Lt)

3. Acid-Base Indicators substances composed of a conjugate weak acid-base pair that changes color with changes in pH see table on pg 10 of Data Book or in the back cover of your text book.

4. the general equation for the reaction occurring in indicators is: where “In” is the indicator formula HIn (aq) + H 2 O (aq) In - (aq) + H 3 O + (aq)

5. Le Chatelier’s Principle is applied to determine the color change when an acid (H 3 O + (aq) ) is added, adding a product shifts the reaction left causing the corresponding color change adding a base will remove H 3 O + (aq)

6. Predict the color of each for the specified pH: bromocresol green at 2.8 phenol red at 8.5 cresol red at 1.6 cresol red at 8.0 methyl violet at 1.0

7. answers bromocresol green at 2.8=yellow phenol red at 8.5=red cresol red at 1.6=yellow cresol red at 8.0=orange ( red/yellow) methyl violet at 1.0=green ( yellow/blue)

8. A solution was tested with several indicators to determine the pH. The following results were obtained. What is the pH of the solution? orange IV - yellow, bromoscresol green - blue, phenol red - yellow, and bromothymol blue - yellow.

9. answer orange IV – yellow so pH>2.8 bromoscresol green – blue so pH>5.4 phenol red – yellow so pH<6.6 bromothymol blue – yellow so pH <6.0 So the 5.4<pH<6.0

10. assignment Read page 245-247 Lab exercise 6.B on page 247 Do page 247 #1-4