Indicators & Table M

pH Indicators Indicators are compounds which turn different colors when H+ is added and taken away. For example, phenolphthalein appears pink in basic solutions because the extra H+ has been removed. When in acid, the solution is clear because the H+ is present. Because the H+ can be easily removed or returned, this indicator can change back and forth from pink to clear a limitless number of times. The equilibrium reaction for phenolphthalein is as follows. HIn (aq) + H2O (l) ↔ H3O+ (aq) + In- (aq) Colorless PinkTable M: Table M 1. Look at Table M in your reference tables. What pH range is phenolphthalein colorless? 0-82. When an acid is added, the amount of H3O+ is increased and the reaction shifts left turning the phenolphthein colorless.3. Look at Table M in your reference tables. What pH range is phenolphthalein pink? 9-144. Bases have hydroxide ions that remove H3O+ from solution. When adding a base the reaction will shift right turning the phenolphthalein pink. What Color is the Indicator? The pH for a substance will be provided. Use Table M to determine the color each indicator will turn in the presence of each substance. Substance pH Color in Methyl Orange Color in Bromthymol Blue Color in Phenolphthalein Stomach Acid - 2 red yellow colorless Cola Drink - 3 red yellow colorless Blood - 7.5 yellow green colorless Pure Water - 7 yellow green colorless Oven Cleaner - 14 yellow blue pink Tomatoes - 4 orange yellow colorless Milk - 6.5 yellow green colorless Detergent - 10 yellow blue pink Coffee - 5 yellow yellow colorless What Color is the Indicator Continued Determine the color of each indicator. Substance pH Color in Litmus Color in Bromcresol Green Color in Thymol Blue Stomach Acid - 2 red yellow yellow Cola Drink - 3 red yellow yellow Blood - 7.5 purple blue yellow Pure Water - 7 purple blue yellow Oven Cleaner - 14 blue blue blue Tomatoes - 4 red green yellow Milk - 6.5 purple blue yellow Detergent - 10 blue blue blue Coffee - 5 purple green yellow