Problem 32 How would you select an indicato... [FREE SOLUTION]

Chapter 15: Problem 32

How would you select an indicator for a particular acid-base titration?

Short Answer

Expert verified

The selection of an indicator for a particular acid-base titration depends upon the nature of the reaction taking place. The indicator's color change should correspond to the pH at the equivalence point of the titration. Indicator such as phenolphthalein is apt for weak acid-strong base titrations and methyl orange for strong acid-weak base titrations.

Step by step solution

Understand Acid-Base Titration

Acid-base titration is a way to find out the concentration of an acid or base by neutralising it with an acid or base of known concentration. During this process, an indicator is used that changes its color at a specific pH range.

Determine the pH at the Equivalence Point

The equivalence point of a titration is the point at which exactly enough titrant has been added to the analyte to fully neutralise it. The pH at the equivalence point depends on the nature of the acid and base being used. For a strong acid-strong base titration, it is at pH 7, for a strong acid-weak base it's less than 7 and for a weak acid-strong base it's greater than 7.

Select Appropriate Indicator

The indicator should be chosen such that its color change occurs over the pH range of the equivalence point. For instance, phenolphthalein has a range from 8.2 - 10.0 making it appropriate for titrations of weak acids with strong bases, while methyl orange with a range 3.1 - 4.4 is suitable for titrations of strong acids with weak bases.

Unlock Step-by-Step Solutions & Ace Your Exams!

Full Textbook Solutions
Get detailed explanations and key concepts
Unlimited Al creation
Al flashcards, explanations, exams and more...
Ads-free access
To over 500 millions flashcards
Money-back guarantee
We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Equivalence Point

Understanding the equivalence point in an acid-base titration is crucial for effective titration results. The equivalence point is that magical moment when the amount of titrant added exactly neutralizes the analyte in the solution. This point indicates that the number of moles of acid equals the number of moles of base.

For a titration involving a strong acid and a strong base, the equivalence point is typically around a neutral pH of 7. This is because the strong acid and strong base completely neutralize each other.
In the case of a strong acid titrating a weak base, the equivalence point will fall below pH 7. This occurs because a weak base does not completely neutralize the strong acid, resulting in a slightly acidic solution.
Conversely, for a weak acid and strong base titration, expect the equivalence point to be above pH 7, since the weak acid only partially neutralizes, leaving a basic solution.

Recognizing the expected pH at the equivalence point allows for the proper selection of an indicator that will accurately signal this pivotal change.

Indicator Selection

Choosing the right indicator is essential for a successful titration. An indicator should exhibit a clear color change at the pH corresponding to the equivalence point of the titration.
When selecting an indicator, consider the pH range over which the indicator changes color and compare it with the expected pH at the equivalence point. Here's how:

For a strong acid-strong base titration, any indicator that changes color around pH 7 will be suitable, such as bromothymol blue.
When titrating a weak base with a strong acid, pick an indicator like methyl orange which changes color in the acidic range (pH 3.1-4.4).
In the event of a weak acid being titrated with a strong base, use indicators like phenolphthalein that change color in the basic range (pH 8.2-10.0).

By ensuring the color transition of the indicator overlaps the equivalence point pH, the end point of the titration will be accurately visualized.

Titration Indicator

Indicators are special chemicals used in titrations to signal a change in the pH of the solution, indicating the equivalence point has been reached. The right selection can greatly affect the accuracy of your titration results.
Not all indicators work the same way. They have specific pH ranges where they exhibit a visible change of color. This depends on the type of indicator and its chemical structure.

Phenolphthalein is clear in acidic solutions and turns pink as the solution becomes more basic, making it ideal for basic equivalence points.
Methyl red, on the other hand, transitions from red to yellow within a more acidic environment, ideal for acidic equivalence points.
The common litmus test is effective for quick and general identification, but it lacks the precision needed for detailed titrations.

Understanding how different indicators work allows you to choose the most appropriate one for your specific titration, ensuring precise and reliable outcomes.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Recommended explanations on Chemistry Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

91影视

How would you select an indicator for a particular acid-base titration?

Short Answer

Step by step solution

Understand Acid-Base Titration

Determine the pH at the Equivalence Point

Select Appropriate Indicator

Key Concepts

Equivalence Point

Indicator Selection

Titration Indicator

One App. One Place for Learning.

Most popular questions from this chapter

Recommended explanations on Chemistry Textbooks

Chemical Reactions

Physical Chemistry

The Earths Atmosphere

Making Measurements

Ionic and Molecular Compounds

Kinetics

Study anywhere. Anytime. Across all devices.