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Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 65b,c
Chapter 3, Problem 65b,c

b. Determine the exact pKa values, using a calculator.
c. Which is the strongest acid?
1. nitrous acid (HNO2), Ka = 4.0 × 10−4
2. nitric acid (HNO3), Ka = 22
3. bicarbonate (HCO3−), Ka = 6.3 × 10−11
4. hydrogen cyanide (HCN), Ka = 7.9 × 10−10
5. formic acid (HCOOH), Ka = 2.0 × 10−4
6. phosphoric acid (H3PO4), Ka = 2.1

Verified step by step guidance
1
Step 1: Understand the concept of pKa. The pKa value is a measure of the strength of an acid. It is the negative logarithm of the acid dissociation constant (Ka), expressed as \( \text{pKa} = -\log(\text{Ka}) \). Lower pKa values indicate stronger acids.
Step 2: Gather the Ka values for the acids in question. If the Ka values are not provided, you may need to look them up in a reliable reference source or database.
Step 3: Use the formula \( \text{pKa} = -\log(\text{Ka}) \) to calculate the pKa for each acid. Input the Ka values into a scientific calculator to determine the exact pKa values.
Step 4: Compare the calculated pKa values. The acid with the lowest pKa value is the strongest acid because it dissociates more completely in solution.
Step 5: Interpret the results and identify the strongest acid based on the comparison of pKa values. Ensure that your calculations are accurate and consistent.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

pKa and Acid Strength

pKa is a quantitative measure of the strength of an acid in solution. It is the negative logarithm of the acid dissociation constant (Ka), which indicates how well an acid donates protons (H+) to a solution. A lower pKa value corresponds to a stronger acid, as it signifies a greater tendency to lose protons.
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Identifying pKa values

Acid-Base Equilibrium

Acid-base equilibrium refers to the balance between the concentrations of acids and their conjugate bases in a solution. This equilibrium is influenced by factors such as concentration, temperature, and the presence of other substances. Understanding this concept is crucial for determining the pKa values and comparing the strengths of different acids.
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Using a Calculator for pKa Values

Calculating pKa values typically involves using a scientific calculator to compute the negative logarithm of the Ka values. This process requires accurate input of the Ka values, which can be obtained from tables or experimental data. Familiarity with logarithmic functions is essential for performing these calculations correctly.
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Related Practice
Textbook Question

From which of the following compounds can HO− remove a proton in a reaction that favors product formation?

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Tenormin, a member of the group of drugs known as beta-blockers, is used to treat high blood pressure and improve survival after a heart attack. It works by slowing down the heart to reduce its workload. Which atom in Tenormin is the most basic?

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Textbook Question

For each of the following pairs of reactions, indicate which one has the more favorable equilibrium constant (that is, which one most favors products):

1.

2.

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Textbook Question

A single bond between two carbons with different hybridizations has a small dipole. What is the direction of the dipole in the indicated bonds?

a.

b.

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Textbook Question

Given the Ka values, estimate the pKa value of each of the following acids without using a calculator (that is, is it between 3 and 4, between 9 and 10, and so on?):

1. nitrous acid (HNO2), Ka = 4.0 × 10−4

2. nitric acid (HNO3), Ka = 22

3. bicarbonate (HCO3−), Ka = 6.3 × 10−11

4. hydrogen cyanide (HCN), Ka = 7.9 × 10−10

5. formic acid (HCOOH), Ka = 2.0 × 10−4

6. phosphoric acid (H3PO4), Ka = 2.1

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Textbook Question

For each compound, indicate the atom that is most apt to be protonated.

a.

b.

c.

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