Unit 6: Acid-Base Applications Lesson 2: Indicators

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

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

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

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

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