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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 \(\mathrm{H}-\) A molecules increases with increasing size of \(\mathrm{A} .\) (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.

Short Answer

Expert verified
Statement (a) is true: acid strength in a series of H-A molecules increases with increasing size of A, as the bond between H and A becomes weaker when A is larger. Statement (b) is false: acid strength actually increases with increasing electronegativity of the central atom, as it weakens the H-A bond and stabilizes the conjugate base. Statement (c) is false: the strongest acid known is fluoroantimonic acid (HSbF6) due to its complete dissociation in solution, providing a high concentration of protons (H+).

Step by step solution

01

Statement (a) Analysis:

The first statement says that acid strength in a series of \(\mathrm{H}-\) A molecules increases with increasing size of \(\mathrm{A}\). To evaluate this statement, we must consider the factors that affect acid strength such as bond strength and stability of the conjugate base (A-).
02

Statement (a) True or False:

The statement (a) is generally true, especially in the case of oxoacids. As the size of A increases, the bond between H and A becomes weaker, and the resulting conjugate base (A-) becomes more stable due to the electron density being more spread out. The weaker bond makes it easier for the compound to release a proton (H+), which means the acid strength increases with the increasing size of A.
03

Statement (b) Analysis:

The second statement says that acid strength decreases with increasing electronegativity of the central atom in acids of the same general structure. To evaluate this statement, we must consider how electronegativity affects the ability of a compound to release protons.
04

Statement (b) True or False:

The statement (b) is false. For acids of the same general structure, the acid strength actually increases with increasing electronegativity of the central atom. The reason is that higher electronegativity will draw electron density away from the H-A bond, therefore, making the bond weaker, and easier to break. Also, a higher electronegative central atom stabilizes the conjugate base after donating a proton. So, the correct statement should be: For acids of the same general structure but differing electronegativities of the central atoms, acid strength increases with increasing electronegativity of the central atom.
05

Statement (c) Analysis:

The third statement claims that the strongest acid known is HF because fluorine is the most electronegative element. To evaluate this statement, we need to compare the acidity of HF with other strong acids.
06

Statement (c) True or False:

The statement (c) is false. Although fluorine is the most electronegative element, its small size results in a strong H-F bond, making HF a weak acid compared to other strong acids like H2SO4 or HCl. The strongest acid known is fluoroantimonic acid (HSbF6), formed by the reaction of hydrogen fluoride (HF) and antimony pentafluoride (SbF5). So, the correct statement should be: The strongest acid known is fluoroantimonic acid (HSbF6) because it dissociates completely in solution, providing a very high concentration of protons (H+).

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