Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 15: Problem 82

Amino acids are the building blocks for all proteins in our bodies. A structure for the amino acid alanine is All amino acids have at least two functional groups with acidic or basic properties. In alanine, the carboxylic acid group has \(K_{\mathrm{a}}=4.5 \times 10^{-3}\) and the amino group has \(K_{\mathrm{b}}=7.4 \times 10^{-5} .\) Because of the two groups with acidic or basic properties, three different charged ions of alanine are possible when alanine is dissolved in water. Which of these ions would predominate in a solution with \(\left[\mathrm{H}^{+}\right]=1.0 M ?\) In a solution with \(\left[\mathrm{OH}^{-}\right]=\) \(1.0 M ?\)

Short Answer

Expert verified
In a solution with \(\left[\mathrm{H}^{+}\right]=1.0 \mathrm{M}\), the cation species (C) would predominate. In a solution with \(\left[\mathrm{OH}^{-}\right]=1.0 \mathrm{M}\), the anion species (A) would predominate.

Step by step solution

01

Determine the balance equation of alanine species and their pK values

Since we have the \(K_{\mathrm{a}}\) and \(K_{\mathrm{b}}\) values for the carboxylic acid and amino groups, respectively, we can determine their pK values: \(pK_{\mathrm{a}} = -\log_{10}(K_{\mathrm{a}}) = -\log_{10}(4.5 \times 10^{-3}) \) \(pK_{\mathrm{b}} = -\log_{10}(K_{\mathrm{b}}) = -\log_{10}(7.4 \times 10^{-5}) \) Now, let's find the pH and pOH for the given solution concentrations: \(pH = -\log_{10}([\mathrm{H}^{+}])\) \(pOH = -\log_{10}([\mathrm{OH}^{-}])\) For both \([\mathrm{H}^{+}]=1.0M\) and \([\mathrm{OH}^{-}]=1.0M\) solutions, we can calculate the pH and pOH and compare them with the pKa and pKb values to determine the predominant alanine species.
02

Calculate pH and pOH for the given solutions

Now let's calculate the pH and pOH for the given solutions: Solution with \([\mathrm{H}^{+}]=1.0\mathrm{M}\): \(pH = -\log_{10}(1.0) = 0\) \(pOH = 14 - pH = 14\) Solution with \([\mathrm{OH}^{-}]=1.0\mathrm{M}\): \(pOH = -\log_{10}(1.0) = 0\) \(pH = 14 - pOH = 14\)
03

Compare pH, pOH with pKa, pKb and determine the predominant alanine species

Now, let's compare the pH with pKa and pKb values: Solution with \([\mathrm{H}^{+}]=1.0\mathrm{M}\): - Since pH is 0 and pKa < pH < pKb, the cation species (C) will predominate. Solution with \([\mathrm{OH}^{-}]=1.0\mathrm{M}\): - Since pH is 14 and pKb < pH, the anion species (A) will predominate. Now, we have determined which alanine species predominate in the given solutions: For a solution with \(\left[\mathrm{H}^{+}\right]=1.0 \mathrm{M}\), the cation species (C) would predominate. For a solution with \(\left[\mathrm{OH}^{-}\right]=1.0 \mathrm{M}\), the anion species (A) would predominate.

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

Methyl red has the following structure: CN(C)c1ccc(N=Nc2ccccc2C(=O)O)cc1 It undergoes a color change from red to yellow as a solution gets more basic. Calculate an approximate \(\mathrm{pH}\) range for which methyl red is useful. What is the color change and the \(\mathrm{pH}\) at the color change when a weak acid is titrated with a strong base using methyl red as an indicator? What is the color change and the \(\mathrm{pH}\) at the color change when a weak base is titrated with a strong acid using methyl red as an indicator? For which of these two types of titrations is methyl red a possible indicator?

Consider a solution formed by mixing \(50.0 \mathrm{~mL}\) of \(0.100 \mathrm{M}\) \(\mathrm{H}_{2} \mathrm{SO}_{4}, 30.0 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{HOCl}, 25.0 \mathrm{~mL}\) of \(0.200 \mathrm{M} \mathrm{NaOH}\). \(25.0 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\), and \(10.0 \mathrm{~mL}\) of \(0.150 \mathrm{M} \mathrm{KOH}\). Calculate the \(\mathrm{pH}\) of this solution.

A student titrates an unknown weak acid, HA, to a pale pink phenolphthalein end point with \(25.0 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{NaOH}\). The student then adds \(13.0 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{HCl}\). The \(\mathrm{pH}\) of the resulting solution is \(4.7\). How is the value of \(\mathrm{p} K_{\mathrm{a}}\) for the unknown acid related to \(4.7 ?\)

Calculate the \(\mathrm{pH}\) of a solution prepared by mixing \(250 . \mathrm{mL}\) of \(0.174 \mathrm{~m}\) aqueous \(\mathrm{HF}\) (density \(=1.10 \mathrm{~g} / \mathrm{mL}\) ) with \(38.7 \mathrm{~g}\) of an aqueous solution that is \(1.50 \% \mathrm{NaOH}\) by mass (density \(=1.02\) \(\mathrm{g} / \mathrm{mL}\) ). \(\left(K_{\mathrm{a}}\right.\) for \(\mathrm{HF}=7.2 \times 10^{-4}\).)

What volumes of \(0.50 \mathrm{M} \mathrm{HNO}_{2}\) and \(0.50 \mathrm{M} \mathrm{NaNO}_{2}\) must be mixed to prepare \(1.00 \mathrm{~L}\) of a solution buffered at \(\mathrm{pH}=3.55\) ?
See all solutions

Recommended explanations on Chemistry Textbooks

Chemical Reactions

Read Explanation

Chemical Analysis

Read Explanation

Organic Chemistry

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Chemistry Branches

Read Explanation

Kinetics

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