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.

Verified step by step guidance

1. (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.
2. (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.
3. (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.

Key Concepts

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.

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.

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.