Textbook Question
Based on their compositions and structures and on conjugate acid–base relationships, select the stronger base in each of the following pairs: (b) BrO- or BrO2-
Ch.16 - Acid-Base Equilibria
Chapter 16, Problem 92
Indicate whether each of the following statements is true or false. For each statement that is false, correct the statement to make it true. (a) Acid strength in a series of H¬A molecules increases with increasing size of A. (b) For acids of the same general structure but differing electronegativities of the central atoms, acid strength decreases with increasing electronegativity of the central atom. (c) The strongest acid known is HF because fluorine is the most electronegative element.
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(a) Consider the trend of acid strength in a series of H-A molecules. Acid strength generally increases with increasing size of the atom A because larger atoms can better stabilize the negative charge after losing a proton (H+). Therefore, the statement is true.
(b) Examine the effect of electronegativity on acid strength for acids with the same general structure. Acid strength actually increases with increasing electronegativity of the central atom because more electronegative atoms can better stabilize the negative charge. Therefore, the statement is false. Corrected statement: For acids of the same general structure, acid strength increases with increasing electronegativity of the central atom.
(c) Evaluate the claim about HF being the strongest acid. While fluorine is the most electronegative element, HF is not the strongest acid. Strong acids are typically those that completely dissociate in water, such as HCl, HBr, and HI. HF is a weak acid because it does not completely dissociate in water. Therefore, the statement is false. Corrected statement: HF is not the strongest acid; it is a weak acid because it does not completely dissociate in water.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid Strength and Atomic Size
In a series of binary acids (H-A), acid strength generally increases with the size of the atom A. This is because larger atoms can stabilize the negative charge of the conjugate base more effectively after the acid donates a proton, leading to a stronger acid. For example, HCl is a stronger acid than HF due to the larger size of Cl compared to F.
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Comparing Binary Acid Strength
Electronegativity and Acid Strength
For acids with the same structure but different central atoms, acid strength typically decreases with increasing electronegativity of the central atom. This is because more electronegative atoms hold onto their electrons more tightly, making it harder for the acid to donate a proton. Thus, acids like HCl are stronger than those like H2O, where oxygen is more electronegative than chlorine.
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01:58Comparing Binary Acid Strength
Strongest Acids and HF
HF (hydrofluoric acid) is not the strongest acid known, despite fluorine being the most electronegative element. HF is a weak acid because the strong bond between H and F makes it less likely to dissociate into H+ and F-. Stronger acids, such as H2SO4 or HCl, have weaker bonds and dissociate more readily, making them stronger in terms of acid strength.
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00:51Comparing Binary Acid Strength Example
Related Practice
Textbook Question
Based on their compositions and structures and on conjugate acid–base relationships, select the stronger base in each of the following pairs: (b) PO43- or AsO43-
Textbook Question
Indicate whether each of the following statements is true or false. For each statement that is false, correct the statement to make it true. (a) In general, the acidity of binary acids increases from left to right in a given row of the periodic table. (b) In a series of acids that have the same central atom, acid strength increases with the number of hydrogen atoms bonded to the central atom. (c) Hydrotelluric acid 1H2Te2 is a stronger acid than H2S because Te is more electronegative than S.
Textbook Question
The fluoride ion reacts with water to produce HF. (c) Is fluoride acting as a Lewis acid or as a Lewis base when reacting with water?
Textbook Question
Identify the Lewis acid and Lewis base among the reactants in each of the following reactions:
(a) Fe(ClO4)3(s) + 6 H2O(l) ⇌ [Fe(H2O)6]3+(aq) + 3 ClO4-(aq)
(b) CN-(aq) + H2O(l) ⇌ HCN(aq) + OH-(aq)
(c) (CH3)3N(g) + BF3(g) ⇌ (CH3)NBF3(s)
(d) HIO(lq) + NH2-(lq) ⇌ NH3(lq) + IO-(lq) (lq denotes liquid ammonia as solvent)