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Ch.16 - Aqueous Equilibria: Acids & Bases
Chapter 16, Problem 79c

Which of the indicators given in Figure 16.5, methyl violet, bromcresol green, phenol red, or thymolphthalein, would be most appropriate to detect a pH change from: (c) 2 to 0?
Color chart showing pH ranges for acid-base indicators: thymol blue, phenol red, bromothymol blue, chlorophenol red.

Verified step by step guidance
1
Identify the pH range of interest, which is from 2 to 0.
Review the pH range of each indicator: Methyl violet, Bromcresol green, Phenol red, and Thymolphthalein.
Determine which indicator has a color change range that includes the pH range from 2 to 0.
Methyl violet typically changes color in the pH range of 0 to 1.6, making it suitable for detecting changes from 2 to 0.
Conclude that Methyl violet is the most appropriate indicator for detecting a pH change from 2 to 0.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 0 to 6 indicates acidic conditions, while a pH of 7 is neutral, and 8 to 14 indicates basic conditions. Understanding the pH scale is crucial for selecting appropriate indicators that change color at specific pH levels.
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Acid-Base Indicators

Acid-base indicators are substances that change color in response to changes in pH. Each indicator has a specific pH range over which it changes color, making it suitable for detecting pH changes in that range. For example, phenol red changes from yellow in acidic conditions to red in neutral to basic conditions, while thymolphthalein transitions from colorless in acidic to blue in basic conditions.
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Choosing the Right Indicator

Selecting the appropriate indicator for a specific pH range is essential for accurate pH detection. In this case, to detect a pH change from 2 to 0, an indicator that operates effectively in the acidic range (0-6) is needed. Analyzing the color change ranges of the indicators provided will help determine which one is most suitable for this specific pH transition.
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