Chapter 3: Problem 77
A student conducted the titration of an amino acid with a strong base. The point in the titration when \(50 \%\) of the amino acid exists as a zwitterion is called: A. the isoelectric point. B. the equivalence point. C. the half-equivalence point. D. the end point.
Short Answer
Expert verified
A. the isoelectric point.
Step by step solution
01
- Understand Key Concepts
First, understand the key concepts involved. A zwitterion is a molecule that has both positive and negative charges but is overall neutral. The isoelectric point (pI) is the pH at which a particular molecule carries no net electrical charge. In titration, the equivalence point is where the amount of titrant equals the amount of substance being titrated, the half-equivalence point is where half of the analyte is neutralized, and the end point is where the indicator changes color.
02
- Identify Relevant Concept
Identify which concept relates to the condition where 50% of the amino acid exists as a zwitterion. This state is crucial during the titration of amino acids because they can act as both acids and bases. When 50% exists as a zwitterion, the solution is at its isoelectric point.
03
- Match the Concept with Options
Match the concept '50% as a zwitterion' with the given options. The isoelectric point (Option A) is the pH where the amino acid is neutral. The equivalence point (Option B) relates to equal amounts of titrant and analyte. The half-equivalence point (Option C) is where half of the reaction is complete. The end point (Option D) is where the indicator shows the completion of the titration.
04
- Choose the Correct Answer
The correct answer is the isoelectric point because it is defined as the pH at which the amino acid exists predominantly as a zwitterion. Therefore, when 50% of the amino acid is a zwitterion, it matches the definition of the isoelectric point.
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 Vaia!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Isoelectric Point
The isoelectric point (pI) is a critical concept in the study of amino acids and proteins. It is defined as the pH at which a particular molecule carries no net electrical charge. For amino acids, this occurs when the amino acid exists predominantly as a zwitterion.
At the isoelectric point, the positive and negative charges on the molecule balance each other out. This neutral charge state impacts the solubility and mobility of the amino acid in an electric field, which is useful in techniques like isoelectric focusing.
Moreover, the isoelectric point is specific to each amino acid because it depends on the side chains of the amino acids. Amino acids with acidic side chains will have lower pI values, while those with basic side chains will have higher pI values. Understanding the isoelectric point is crucial for predicting the behavior of amino acids in different pH environments.
At the isoelectric point, the positive and negative charges on the molecule balance each other out. This neutral charge state impacts the solubility and mobility of the amino acid in an electric field, which is useful in techniques like isoelectric focusing.
Moreover, the isoelectric point is specific to each amino acid because it depends on the side chains of the amino acids. Amino acids with acidic side chains will have lower pI values, while those with basic side chains will have higher pI values. Understanding the isoelectric point is crucial for predicting the behavior of amino acids in different pH environments.
Zwitterion
A zwitterion is a unique type of molecule that contains both positive and negative charges, yet is overall electrically neutral. In amino acids, the zwitterion form is a common occurrence. This happens when the amino group (NH3+) is protonated, and the carboxyl group (COO-) is deprotonated.
In solution, amino acids can exist in different forms depending on the pH of the environment. At a certain pH, typically close to the isoelectric point, the amino acid will predominantly exist as a zwitterion. This form is important because it represents a balance between acidity and basicity within the molecule.
Understanding zwitterions is important in biochemistry and molecular biology as it influences the solubility, structure, and function of amino acids and peptides.
In solution, amino acids can exist in different forms depending on the pH of the environment. At a certain pH, typically close to the isoelectric point, the amino acid will predominantly exist as a zwitterion. This form is important because it represents a balance between acidity and basicity within the molecule.
Understanding zwitterions is important in biochemistry and molecular biology as it influences the solubility, structure, and function of amino acids and peptides.
Equivalence Point
The equivalence point in titration is a significant milestone. It is the point at which the amount of titrant added is exactly enough to neutralize the analyte in the solution. For amino acids, this is the point where the base added has completely reacted with the acidic groups present.
Reaching the equivalence point is crucial because it signifies that stoichiometrically equivalent quantities of reactants have been mixed. In the context of amino acids, this is typically observed as a sharp change in pH. Titration curves often show a steeper slope at this stage.
In titration experiments, identifying the equivalence point helps calculate the concentration of unknown solutions accurately. It is different from the end point, where the color change of an indicator signals the completion of the titration.
Reaching the equivalence point is crucial because it signifies that stoichiometrically equivalent quantities of reactants have been mixed. In the context of amino acids, this is typically observed as a sharp change in pH. Titration curves often show a steeper slope at this stage.
In titration experiments, identifying the equivalence point helps calculate the concentration of unknown solutions accurately. It is different from the end point, where the color change of an indicator signals the completion of the titration.
Half-Equivalence Point
The half-equivalence point is an interesting phase in a titration process. At this point, half of the analyte (the substance being titrated) has been neutralized by the titrant. For amino acids, this means that 50% of the acidic protons have been removed.
One critical aspect of the half-equivalence point is that the pH at this stage equals the pKa of the analyte. This relationship is derived from the Henderson-Hasselbalch equation. Thus, the half-equivalence point provides valuable information about the pKa values of amino acids and other compounds.
Understanding the half-equivalence point is vital for constructing titration curves and identifying buffer regions. These regions are where the solution resists changes in pH, which is essential for maintaining stable environments in biological systems and many chemical processes.
One critical aspect of the half-equivalence point is that the pH at this stage equals the pKa of the analyte. This relationship is derived from the Henderson-Hasselbalch equation. Thus, the half-equivalence point provides valuable information about the pKa values of amino acids and other compounds.
Understanding the half-equivalence point is vital for constructing titration curves and identifying buffer regions. These regions are where the solution resists changes in pH, which is essential for maintaining stable environments in biological systems and many chemical processes.
