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Ch.17 - Acids and Bases
All textbooksTro 5th EditionCh.17 - Acids and BasesProblem 119
Chapter 17, Problem 119

Based on their molecular structure, pick the stronger acid from each pair of oxyacids. Explain your choice for the following pairs: a. H2SO4 or H2SO3 b. HClO2 or HClO c. HClO or HBrO d. CCl3COOH or CH3COOH.

Verified step by step guidance
1
insert step 1: Understand that the strength of an oxyacid is influenced by the electronegativity of the central atom and the number of oxygen atoms bonded to it.
insert step 2: For pair (a) H2SO4 vs. H2SO3, note that H2SO4 has more oxygen atoms than H2SO3, which increases its ability to stabilize the negative charge after losing a proton, making it a stronger acid.
insert step 3: For pair (b) HClO2 vs. HClO, recognize that HClO2 has more oxygen atoms than HClO, which enhances its acid strength due to better charge distribution and stabilization.
insert step 4: For pair (c) HClO vs. HBrO, consider the electronegativity of the central atom; chlorine is more electronegative than bromine, making HClO a stronger acid.
insert step 5: For pair (d) CCl3COOH vs. CH3COOH, observe that the presence of electronegative chlorine atoms in CCl3COOH increases its acidity compared to CH3COOH, as they withdraw electron density and stabilize the conjugate base.

Key Concepts

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

Oxyacids and Their Strength

Oxyacids are acids that contain oxygen, hydrogen, and another element. The strength of an oxyacid is influenced by the number of oxygen atoms bonded to the central atom; more oxygen typically leads to stronger acids. This is because additional oxygen atoms stabilize the negative charge on the conjugate base after deprotonation, making it easier for the acid to donate a proton.
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Electronegativity and Acid Strength

The electronegativity of the central atom in an oxyacid affects its acidity. A more electronegative central atom can better stabilize the negative charge of the conjugate base, enhancing the acid's ability to donate protons. For example, in the pair HClO2 and HClO, the higher electronegativity of chlorine in HClO2 contributes to its greater acidity compared to HClO.
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Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents on the acidity of a compound. In carboxylic acids, such as CCl3COOH and CH3COOH, the presence of electronegative groups like Cl can increase acidity by stabilizing the conjugate base through the inductive effect, making the acid stronger. This effect is crucial in comparing the strength of acids with different substituents.
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Related Practice
Textbook Question

Consider a 0.10 M solution of a weak polyprotic acid (H2A) with the possible values of Ka1 and Ka2 given here.

a. Ka1 = 1.0 × 10–4; Ka2 = 5.0 × 10–5

Calculate the contributions to [H3O+] from each ionization step. At what point can the contribution of the second step be neglected?

Textbook Question

Based on molecular structure, arrange the binary compounds in order of increasing acid strength. Explain your choice. H2Te, HI, H2S, NaH

Textbook Question

Based on molecular structure, arrange the oxyacids in order of increasing acid strength. Explain your choice. HClO3, HIO3, HBrO3

Textbook Question

Which is a stronger base, S2– or Se2–? Explain.