Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 17: Problem 106

Amino acids are the building blocks of proteins. These compounds contain at least one amino group and one carboxyl group. Consider glycine, whose structure is shown in Figure 11.18 . Depending on the \(\mathrm{pH}\) of the solution, glycine can exist in one of three possible forms: Fully protonated: \(\mathrm{NH}_{3}-\mathrm{CH}_{2}-\mathrm{COOH}\) Dipolar ion: \(\mathrm{NH}_{3}-\mathrm{CH}_{2}-\mathrm{COO}^{-}\) Fully ionized: \(\mathrm{NH}_{2}-\mathrm{CH}_{2}-\mathrm{COO}^{-}\) Predict the predominant form of glycine at \(\mathrm{pH} 1.0,\) \(7.0,\) and \(12.0 .\) The \(\mathrm{p} K_{\mathrm{a}}\) of the carboxyl group is 2.3 and that of the ammonium group is 9.6.

Short Answer

Expert verified
At pH 1.0, glycine would primarily be in the fully protonated form (\(\mathrm{NH}_{3}^{+}\mathrm{CH}_{2}\mathrm{COOH}\)). At pH 7.0, it would be in the dipolar ion form (\(\mathrm{NH}_{3}^{+}\mathrm{CH}_{2}\mathrm{COO}^{-}\)). At pH 12.0, it would mostly be in the fully ionized form (\(\mathrm{NH}_{2}\mathrm{CH}_{2}\mathrm{COO}^{-}\)).

Step by step solution

01

Predict the form at pH 1.0

pH 1.0 is very acidic. In this environment, most groups will be protonated. So, glycine will exist primarily in its fully protonated form: \(\mathrm{NH}_{3}^{+}\mathrm{CH}_{2}\mathrm{COOH}\).
02

Predict the form at pH 7.0

pH 7.0 is neutral. Here, the carboxyl group will lose a proton becoming a carboxylate ion (-COO-) because its pKa (2.3) is less than the solution pH. However, the ammonium group will remain protonated because its pKa (9.6) is greater than pH 7. Thus, glycine will primarily exist as a dipolar ion: \(\mathrm{NH}_{3}^{+}\mathrm{CH}_{2}\mathrm{COO}^{-}\).
03

Predict the form at pH 12.0

pH 12.0 is very basic. In this environment, both ammonium and carboxyl groups will lose protons. The pKa values for both functional groups are less than the pH of the solution, therefore, both will be deprotonated. Thus, glycine will exist primarily in its fully ionized form: \(\mathrm{NH}_{2}\mathrm{CH}_{2}\mathrm{COO}^{-}\).

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

The \(\mathrm{p} K_{\mathrm{b}}\) s for the bases \(\mathrm{X}^{-}, \mathrm{Y}^{-},\) and \(Z^{-}\) are 2.72 \(8.66,\) and \(4.57,\) respectively. Arrange the following acids in order of increasing strength: HX, HY, HZ.

The solubility product of \(\mathrm{Mg}(\mathrm{OH})_{2}\) is \(1.2 \times 10^{-11}\) What minimum \(\mathrm{OH}^{-}\) concentration must be attained (for example, by adding \(\mathrm{NaOH}\) ) to make the \(\mathrm{Mg}^{2+}\) concentration in a solution of \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) less than \(1.0 \times 10^{-10} M ?\)

Explain, with balanced ionic equations, why (a) \(\mathrm{CuI}_{2}\) dissolves in ammonia solution, (b) AgBr dissolves in NaCN solution, (c) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\) dissolves in \(\mathrm{KCl}\) solution.

Specify which of these systems can be classified as a buffer system: (a) \(\mathrm{KCl} / \mathrm{HCl}\), (b) \(\mathrm{NH}_{3} / \mathrm{NH}_{4} \mathrm{NO}_{3}\) (c) \(\mathrm{Na}_{2} \mathrm{HPO}_{4} / \mathrm{NaH}_{2} \mathrm{PO}_{4}\)

A 0.2688 -g sample of a monoprotic acid neutralizes \(16.4 \mathrm{~mL}\) of \(0.08133 \mathrm{M}\) KOH solution. Calculate the molar mass of the acid.
See all solutions

Recommended explanations on Chemistry Textbooks

Physical Chemistry

Read Explanation

Kinetics

Read Explanation

Organic Chemistry

Read Explanation

Inorganic Chemistry

Read Explanation

Chemical Analysis

Read Explanation

Ionic and Molecular Compounds

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