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Ch.16 - Acid-Base Equilibria
Chapter 16, Problem 3a

The indicator methyl orange has been added to both of the following solutions. Based on the colors, classify each statement as true or false: (a) The pH of solution A is definitely less than 7.00.

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<insert step 1> Understand that methyl orange is a pH indicator that changes color depending on the acidity or basicity of a solution.>
<insert step 2> Recall that methyl orange changes from red at a pH of 3.1 to yellow at a pH of 4.4.>
<insert step 3> Consider the color of solution A after adding methyl orange. If the solution is red, it indicates a pH less than 3.1. If it is yellow, the pH is above 4.4.>
<insert step 4> If solution A is orange, it suggests a pH between 3.1 and 4.4.>
<insert step 5> Conclude that if solution A is red or orange, the pH is definitely less than 7.00. If it is yellow, further information is needed to determine if the pH is less than 7.00.>

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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 less than 7 indicates an acidic solution, while a pH greater than 7 indicates a basic solution. A pH of exactly 7 is considered neutral. Understanding the pH scale is essential for interpreting the results of acid-base indicators like methyl orange.
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Acid-Base Indicators

Acid-base indicators are substances that change color in response to changes in pH. Methyl orange, for example, turns red in acidic solutions (pH < 3.1) and yellow in neutral to basic solutions (pH > 4.4). Knowing how these indicators behave at different pH levels helps in determining the acidity or basicity of a solution based on its color.
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Color Change Interpretation

Interpreting the color change of an indicator in a solution is crucial for determining its pH. If methyl orange is red, it suggests the solution is acidic (pH < 3.1), while a yellow color indicates a neutral or basic solution (pH > 4.4). This understanding allows for accurate classification of the solution's pH based on the observed color.
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