/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 3 Briefly describe two methods for... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 16: Problem 3

Briefly describe two methods for determining \(K_{a}\) for a weak acid.

Short Answer

Expert verified
Determine \(K_a\) of a weak acid using titration (at half-equivalence point \(pH = pK_a\)) and conductivity (applying degree of dissociation).

Step by step solution

01

Method of Titration Curve

A titration curve can be used to determine the dissociation constant \(K_a\) of a weak acid. By titrating the weak acid with a strong base and plotting the pH against the volume of base added, you can identify the half-equivalence point. At this point, the concentration of the weak acid equals that of its conjugate base. The pH at this half-equivalence point is equal to the \(pK_a\), because \(pH = pK_a + \log(1)\). From \(pK_a\), you can find \(K_a\) by the relation \(K_a = 10^{-pK_a}\).
02

Method of Conductivity

Conductivity measurements provide another method to calculate \(K_a\). As the weak acid partially dissociates in solution, it contributes to the conductivity through its ions. The degree of dissociation \(\alpha\) can be determined by comparing the measured molar conductivity of the acid at a given concentration to its limiting molar conductivity at infinite dilution. \(K_a\) can be calculated using \(K_a = c \alpha^2 / (1 - \alpha)\), where \(c\) is the concentration of the acid.

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.

Titration Curve
A titration curve is a vital tool used in chemistry to understand the dissociation constant, commonly referred to as \(K_a\), of a weak acid.
By titrating the weak acid with a strong base and plotting the pH values against the volume of base added, a sigmoidal curve is often produced.

This curve can be used to identify critical points, such as the half-equivalence point:
  • At the half-equivalence point, the amount of added base has neutralized half of the weak acid.
  • The concentration of the weak acid equals that of the conjugate base.
  • The pH at this point is particularly important because it equals the \(pK_a\) of the acid.
Once the \(pK_a\) value is identified, you can easily calculate \(K_a\) using the formula \(K_a = 10^{-pK_a}\). This process provides an accurate means to pinpoint the dissociation characteristics of weak acids, enabling chemists to predict behavior in varying conditions.
Conductivity
Conductivity measurements offer another insightful method to determine the acid dissociation constant, \(K_a\), for weak acids.
In water, weak acids partially dissociate into ions, which affect the solution's conductivity.

To find \(K_a\) using conductivity:
  • Begin by measuring the molar conductivity of the solution containing the weak acid at a certain concentration \(c\).
  • Compare this value to the limiting molar conductivity at infinite dilution, which is when all the acid is dissociated.
  • The degree of dissociation \(\alpha\) can then be determined by the ratio of these conductivities.
Once \(\alpha\) is calculated, \(K_a\) can be found using the formula \(K_a = c \alpha^2 / (1 - \alpha)\).
This method provides a practical approach, especially in cases where direct pH measurements might not be feasible.
Weak Acid Dissociation
Weak acids are characterized by their incomplete dissociation in water, meaning they do not donate all available hydrogen ions (H\(^+\)) to the solution.
This process of partial dissociation is quantitatively described by the acid dissociation constant, \(K_a\).

The concept of \(K_a\) is crucial for several reasons:
  • It measures the strength of a weak acid, with lower \(K_a\) values indicating weaker acids.
  • The dissociation involves creating equilibrium between the undissociated acid and its ions, often written as \(HA \rightleftharpoons H^+ + A^-\).
  • Understanding \(K_a\) allows chemists to predict how the acid will behave in different chemical environments.
By knowing \(K_a\), you can better understand the subtle balances within weak acid solutions, which aids in applications ranging from pharmaceuticals to food chemistry.

One App. One Place for Learning.

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

Get started for free

Most popular questions from this chapter

Write the equation for the ionization of aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\), in aqueous solution. Write the expression for \(K_{b}\).

The pH of a white vinegar solution is \(2.45 .\) This vinegar is an aqueous solution of acetic acid with a density of \(1.09 \mathrm{~g} / \mathrm{mL}\). What is the mass percentage of acetic acid in the solution?

What is the \(\mathrm{pH}\) of a buffer solution that is \(0.15 \mathrm{M}\) chloroacetic acid and \(0.10 M\) sodium chloroacetate? \(K_{a}=\) \(1.3 \times 10^{-3}\)

Write the equation for the acid ionization of the \(\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+}\) ion.

A \(0.108 M\) sample of a weak acid is \(4.16 \%\) ionized in solution. What is the hydroxide concentration of this solution?
See all solutions

Recommended explanations on Chemistry Textbooks

Kinetics

Read Explanation

Nuclear Chemistry

Read Explanation

Organic Chemistry

Read Explanation

Chemistry Branches

Read Explanation

Chemical Analysis

Read Explanation

The Earths Atmosphere

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.