Referring to Table 17.1, pick an indicator for use in the titration of each base with a strong acid. a. CH3NH2

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Identify the type of titration: In this case, we are titrating a weak base (CH3NH2) with a strong acid.

Determine the pH at the equivalence point: For a weak base-strong acid titration, the pH at the equivalence point will be less than 7.

Consult Table 17.1 for indicators: Look for an indicator that changes color in the acidic pH range, specifically around the expected pH at the equivalence point.

Select an appropriate indicator: Choose an indicator whose color change range includes the pH at the equivalence point of the titration.

Verify the choice: Ensure that the selected indicator provides a clear and distinct color change at the equivalence point.

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Key Concepts

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

Acid-Base Titration

An acid-base titration is a quantitative analytical method used to determine the concentration of an acid or base in a solution. It involves the gradual addition of a titrant (a solution of known concentration) to a sample until the reaction reaches its equivalence point, where the amount of acid equals the amount of base. The choice of indicator is crucial, as it signals the endpoint of the titration through a color change.

Indicators

Indicators are substances that change color at a specific pH range, making them useful for determining the endpoint of a titration. Different indicators are suitable for different types of titrations based on the pH at which the equivalence point occurs. For titrations involving strong acids and weak bases, such as CH3NH2 (methylamine), an indicator that changes color in the acidic pH range is typically selected.

pH and pKa

pH is a measure of the acidity or basicity of a solution, while pKa is the negative logarithm of the acid dissociation constant (Ka) of a weak acid. The pKa value helps predict the pH at which an acid or base will be half dissociated. In the context of titration, knowing the pKa of the weak base (like CH3NH2) allows for the selection of an appropriate indicator that will change color at the pH corresponding to the equivalence point of the titration.

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Textbook Question

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