Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 16: Problem 39

Why do we normally not quote \(K_{\mathrm{a}}\) values for strong acids such as \(\mathrm{HCl}\) and \(\mathrm{HNO}_{3}\) ? Why is it necessary to specify temperature when giving \(K_{\mathrm{a}}\) values?

Short Answer

Expert verified
Strong acids like HCl and HNO3 fully ionise in solution giving a very large Ka value which is often not quoted due to its impracticality for comparison or calculations. Ka values depend on temperature because the acid dissociation is a chemical reaction and its equilibrium can be influenced by temperature changes. Therefore it's necessary to specify the temperature at which Ka is measured.

Step by step solution

01

Understanding Ka values for Strong Acids

Strong acids such as Hydrochloric acid (HCl) and Nitric acid (HNO3) are fully ionised in solution. This complete ionisation indicates that there is a complete transfer of protons from the acid to the water molecules. As a result, the ratio of the concentration of the resultant ions to the very minimal concentration of the undissociated acid molecules results in a very large Ka value. Since this Ka value is impractically large for calculations or comparisons, it is often not quoted.
02

Temperature Dependency of Ka

The Ka value is not a constant, but is rather temperature-dependent. This is because the dissociation of an acid is a chemical reaction, and the equilibrium of such reactions is known to be affected by temperature changes according to Le Châtelier's principle. Thus, when the Ka value of an acid is given, the temperature at which this value was measured must also be specified, as the Ka value can change with temperature.

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!

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

To which of the following would the addition of an equal volume of \(0.60 \mathrm{M} \mathrm{NaOH}\) lead to a solution having a lower \(\mathrm{pH} ?\) (a) water, (b) \(0.30 \mathrm{M} \mathrm{HCl}\), (c) \(0.70 \mathrm{M} \mathrm{KOH}\) (d) \(0.40 \mathrm{M} \mathrm{NaNO}_{3}\).

Teeth enamel is largely hydroxyapatite \(\left[\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3} \mathrm{OH}\right]\). When it dissolves in water (a process called demineralization), it dissociates as follows: $$\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3} \mathrm{OH} \longrightarrow 5 \mathrm{Ca}^{2+}+3 \mathrm{PO}_{4}^{3-}+\mathrm{OH}^{-}$$ The reverse process, called remineralization, is the body's natural defense against tooth decay. Acids produced from food remove the \(\mathrm{OH}^{-}\) ions and thereby weaken the enamel layer. Most toothpastes contain a flouride compound such as \(\mathrm{NaF}\) or \(\mathrm{SnF}_{2}\). What is the function of these compounds in preventing tooth decay?

Novocaine, used as a local anesthetic by dentists, is a weak base \(\left(K_{\mathrm{b}}=8.91 \times 10^{-6}\right)\). What is the ratio of the concentration of the base to that of its acid in the blood plasma \((\mathrm{pH}=7.40)\) of a patient?

The \(\mathrm{pH}\) of an HF solution is 6.20 . Calculate the ratio [conjugate base]/[acid] for HF at this pH.

Calculate the \(\mathrm{pH}\) of a solution that is \(1.00 \mathrm{M} \mathrm{HCN}\) and \(1.00 M\) HF. Compare the concentration (in molarity) of the \(\mathrm{CN}^{-}\) ion in this solution with that in a \(1.00 \mathrm{M}\) HCN solution. Comment on the difference.
See all solutions

Recommended explanations on Chemistry Textbooks

Chemical Analysis

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Nuclear Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Making Measurements

Read Explanation

Chemistry Branches

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