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6.3- Acid-Base Indicators

6.3- Acid-Base Indicators. 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). Acid-Base Indicators.

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6.3- Acid-Base Indicators

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  1. 6.3- Acid-Base Indicators

  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)+ H2O(aq) In-(aq)+ H3O+(aq)

  5. Le Chatelier’s Principle is applied to determine the color change • when an acid (H3O+(aq)) is added, adding a product shifts the reaction left causing the corresponding color change • adding a base will remove H3O+(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

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