Ch.4 - Reactions in Aqueous Solution

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 35a

Chapter 4, Problem 35a

Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (a) HF

Verified step by step guidance

Identify the type of compound HF is by analyzing its chemical formula. HF stands for hydrogen fluoride.

Recognize that HF is a binary compound consisting of hydrogen (H) and fluorine (F). In such compounds, hydrogen typically acts as a positive ion (H+).

Determine the nature of HF in solution: HF is known as a weak acid because it does not completely dissociate into its ions in aqueous solution.

Conclude that in aqueous solution, HF exists primarily in molecular form, with a small fraction existing as ions (H+ and F-).

Label HF as an acid that exists in aqueous solution as a mixture of molecules and ions.

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Key Concepts

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

Acids and Bases

Acids are substances that can donate protons (H+) in a solution, while bases are substances that can accept protons. The Brønsted-Lowry theory defines acids and bases based on proton transfer, whereas the Lewis theory defines them based on electron pair donation and acceptance. Understanding these definitions is crucial for classifying substances like HF.

Dissociation in Aqueous Solution

When substances dissolve in water, they can dissociate into ions or remain as molecules. Strong acids and bases typically dissociate completely into ions, while weak acids and bases only partially dissociate. This concept is essential for determining whether a substance exists entirely in molecular form, entirely as ions, or as a mixture in solution.

Weak Acids

HF, or hydrofluoric acid, is classified as a weak acid because it does not completely dissociate in aqueous solution. Instead, it exists in equilibrium between its molecular form and its ions (H+ and F-). Recognizing the behavior of weak acids is important for accurately labeling substances and understanding their properties in solution.

Related Practice

Textbook Question

Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (d) Ba1OH22.

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Textbook Question

State whether each of the following statements is true or false. Justify your answer in each case. (b) HCl is a weak acid.

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Textbook Question

State whether each of the following statements is true or false. Justify your answer in each case.

(c) Although sulfuric acid is a strong electrolyte, an aqueous solution of H₂SO₄ contains more HSO₄^- ions than SO₄^2- ions.

State whether each of the following statements is true or false. Justify your answer in each case. (c) Methanol is a base.

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