Textbook Question
Calculate the pH of 100.0 mL of 0.30 M NH3 before and after the addition of 4.0 g of NH4NO3, and account for the change. Assume that the volume remains constant.
Ch.16 - Aqueous Equilibria: Acids & Bases
Chapter 16, Problem 63c
Identify the weakest acid in each of the following sets. Explain your reasoning. (c) B(OH)3, Al(OH)3, Ga(OH)3
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Identify the chemical nature of each compound: B(OH)3, Al(OH)3, and Ga(OH)3 are all hydroxides of group 13 elements.
Understand the concept of acidity in hydroxides: The acidity of these compounds is related to their ability to donate protons (H+) in water, which is influenced by the central atom's electronegativity and size.
Consider the electronegativity trend: In group 13, electronegativity decreases down the group. Boron (B) is more electronegative than aluminum (Al) and gallium (Ga). Higher electronegativity generally leads to stronger acids because the central atom can better stabilize the negative charge after losing a proton.
Analyze the size and charge density: As you move down the group, the size of the central atom increases, which decreases the charge density and weakens the acid strength. Therefore, Ga(OH)3, with the largest central atom, is expected to be the weakest acid.
Conclude based on trends: Based on the trends in electronegativity and atomic size, Ga(OH)3 is the weakest acid among the given hydroxides because it has the lowest electronegativity and largest atomic size, making it less effective at stabilizing the negative charge after proton donation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid Strength
Acid strength refers to the ability of an acid to donate protons (H+) in a solution. Stronger acids dissociate more completely in water, resulting in a higher concentration of H+ ions. The strength of an acid is often influenced by its molecular structure, electronegativity of atoms, and the stability of its conjugate base.
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Metal Hydroxides as Acids
Metal hydroxides can exhibit acidic properties, particularly when they are amphoteric, meaning they can act as either acids or bases. In the context of the question, B(OH)3, Al(OH)3, and Ga(OH)3 are metal hydroxides that can donate protons, but their acidic strength varies based on the metal's position in the periodic table and its ability to stabilize the negative charge of the hydroxide ion.
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Periodic Trends in Acidic Behavior
Periodic trends indicate that acid strength can change based on the group and period of the elements involved. Generally, as you move down a group in the periodic table, the acidic strength of metal hydroxides increases due to the larger atomic size and lower electronegativity, which affects the stability of the hydroxide ion and the ability to donate protons.
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Related Practice
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Identify the weakest acid in each of the following sets. Explain your reasoning. (b) NH3, H2O, H2S
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Identify the stronger acid in each of the following pairs.Explain your reasoning.(b) H3PO4 or H3AsO4
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Textbook Question
Identify the stronger base in each of the following pairs.
Explain your reasoning.
(a) ClO2- or ClO3-
(b) HSO4- or HSeO4-
Textbook Question
Identify the stronger base in each of the following pairs.
Explain your reasoning.
(c) HS- or OH-