Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 19: Problem 3

What is the common-ion effect? How is it related to Le Châtelier's principle? Explain with equations that include HF and NaF.

Short Answer

Expert verified
The common-ion effect reduces the ionization of a weak electrolyte due to the addition of a common ion, explained by Le Châtelier's principle shifting equilibrium to counteract the disturbance.

Step by step solution

01

- Understand the Common-Ion Effect

The common-ion effect occurs when a weak electrolyte and a strong electrolyte containing a common ion are both dissolved in the same solution. This typically reduces the ionization of the weak electrolyte.
02

- Identify the Chemicals Involved

In this example, the weak acid HF (hydrofluoric acid) and the salt NaF (sodium fluoride) are used. NaF dissociates completely in water to give Na⁺ and F⁻ ions.
03

- Write the Ionization Equations

Write the ionization equation for HF in water:\(\text{HF} \rightleftharpoons \text{H}^+ + \text{F}^-\). For NaF, write: \(\text{NaF} \rightarrow \text{Na}^+ + \text{F}^-\).
04

- Apply the Common-Ion Effect to HF

Adding NaF to a solution of HF increases the concentration of the common ion, F⁻. Due to this, the ionization of HF is suppressed according to the common-ion effect.
05

- Connect to Le Châtelier's Principle

Le Châtelier's principle states that a system at equilibrium will adjust to counteract a disturbance. Adding F⁻ shifts the equilibrium of HF dissociation:\[\text{HF} \rightleftharpoons \text{H}^+ + \text{F}^-\] to the left, reducing the concentration of H⁺ and F⁻ ions.

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.

Start your free trial

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.

Le Châtelier's principle
To understand Le Châtelier's principle, imagine a balance. This principle states that when a system at equilibrium faces a change, it reacts to restore balance by counteracting that change.
In a chemical context, if you add more of a product or reactant to a reaction at equilibrium, the system will shift to consume the added substance.
For example, with the reaction involving HF (hydrofluoric acid) and its dissociation into ions: \[ \text{HF} \rightleftharpoons \text{H}^+ + \text{F}^- \]If you add more F⁻ ions by dissolving NaF (sodium fluoride), the system shifts left to reduce the added F⁻ by forming more HF. This is Le Châtelier's principle in action, maintaining balance.
Weak Electrolyte
A weak electrolyte is a substance that only partially ionizes in solution.
This means that in water, most of the substance stays in its original form, and only a small fraction breaks apart into ions.
Hydrofluoric acid (HF) is an example of a weak electrolyte. When dissolved in water, it does not completely dissociate into H⁺ and F⁻ ions.
This partial ionization can be represented by the equilibrium: \[ \text{HF} \rightleftharpoons \text{H}^+ + \text{F}^- \]The presence of the common ion, F⁻ from NaF, reduces the ionization of HF even further.
Ionization Equilibrium
Ionization equilibrium occurs when the rate of ionization of a substance is equal to the rate of recombination of ions.
For weak electrolytes like HF, this equilibrium is essential since only a portion of the substance ionizes: \[ \text{HF} \rightleftharpoons \text{H}^+ + \text{F}^- \]When you add more F⁻ ions from NaF, this equilibrium shifts in response to Le Châtelier's principle.
The increased concentration of F⁻ causes the equilibrium to shift left, leading to fewer H⁺ and F⁻ ions, and more undissociated HF.
This helps maintain the balance in the system, illustrating the delicate nature of ionization equilibrium in solutions.

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

What is the difference between the end point of a titration and the equivalence point? Is the equivalence point always reached first? Explain.

What is the component concentration ratio, \(\left[\mathrm{BrO}^{-}\right] /[\mathrm{HBrO}]\), of a buffer that has a \(\mathrm{pH}\) of \(7.95\left(K_{\mathrm{a}}\right.\) of \(\left.\mathrm{HBrO}=2.3 \times 10^{-9}\right) ?\)

What is the purpose of an acid-base buffer?

Write the ion-product expressions for (a) calcium chromate; (b) silver cyanide; (c) silver phosphate.

What is the \(p H\) of a solution of \(6.5 \times 10^{-9} \mathrm{~mol}\) of \(\mathrm{Ca}(\mathrm{OH})_{2}\) in \(10.0 \mathrm{~L}\) of water \(\left[K_{\mathrm{sp}}\right.\) of \(\left.\mathrm{Ca}(\mathrm{OH})_{2}=6.5 \times 10^{-6}\right] ?\)
See all solutions

Recommended explanations on Chemistry Textbooks

Chemistry Branches

Read Explanation

Making Measurements

Read Explanation

The Earths Atmosphere

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Chemical Analysis

Read Explanation

Chemical Reactions

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.

Sign-up for free