Questions and Answers
What color does phenolphthalein turn in a basic solution?
Which of the following indicators has a pH range that includes neutral pH?
At what pH range does methyl red change color?
What is the color of bromothymol blue in an acidic solution?
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Which acid-base indicator shows a color change from red to yellow at a pH below 4?
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Study Notes
Acid-Base Indicators Overview
- Acid-base indicators are substances that change color at a specific pH range, useful for determining acidity or alkalinity.
- Each indicator has a unique pKin and pH range where it changes color.
Key Indicators and Their Properties
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Thymol Blue (Acid):
- pKin: 1.7
- pH range: 1.2-2.8
- Color: Red in acidic solutions.
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Bromophenol Blue:
- pKin: 4.1
- pH range: 3.0-4.6
- Color: Yellow in acidic solutions.
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Methyl Orange:
- pKin: 3.7
- pH range: 3.1-4.4
- Color: Red in acidic environments.
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Methyl Red:
- pKin: 5.0
- pH range: 4.2-6.3
- Color: Red in more acidic conditions.
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Congo Red:
- No pKin listed.
- pH range: 3.0-5.0
- Color: Blue in acidic solutions.
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Litmus:
- pKin: 6.5
- pH range: 5.5-7.5
- Color: Red in acidic, Blue in alkaline solutions.
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Phenol Red:
- pKin: 7.8
- pH range: 6.8-8.4
- Color: Yellow in alkaline conditions.
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Thymol Blue (Base):
- pKin: 8.9
- pH range: 8.0-9.6
- Color: Yellow in alkaline solutions.
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Bromothymol Blue:
- pKin: 7.1
- pH range: 6.0-7.6
- Color: Yellow in acidic solutions.
-
Phenolphthalein:
- pKin: 9.7
- pH range: 8.3-10.0
- Color: Colorless in acidic, turns to pink in alkaline solutions.
Color Changes in Different Solutions
- Acidic solutions typically display red colors with indicators like Methyl red, Methyl orange, and Thymol blue (acid).
- Yellow is observed in bromothymol blue and phenol red in acidic solutions.
- Alkaline solutions change color predominantly to yellow or blue, particularly with indicators like Thymol blue (base) and Litmus.
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Description
Test your knowledge on various acid-base indicators, including their pKin values, pH ranges, and color changes. This quiz will help reinforce your understanding of how these indicators function in different pH environments.
