Question
The table above provides information on two weak acids. Which of the following explains the difference in their acid strength?
A Acid 1 is a stronger acid because it has more acidic hydrogen atoms than acid 2.
B Acid 1 is a stronger acid because it can make more hydrogen bonds than acid 2.
C Acid 2 is a stronger acid because it is a larger, more polarizable molecule with stronger intermolecular forces than acid 1.
D Acid 2 is a stronger acid because it has a more stable conjugate base than acid 1 due to the greater number of electronegative Br atoms.
▶️Answer/Explanation
Ans:D
These two acids differ in the substitution of one H atom by a more electronegative Br atom, making the conjugate base \(C_2Br_3O_2^−\) a more stable (weaker) base compared to \(C_2HBr_2O_2^−\). The more stable a conjugate base is, the stronger the weak acid is.
Question
▶️Answer/Explanation
Ans:D
The chemical structure of these acids only show a difference in the central atom. The conjugate bases \(HTeO_4^−\) and \(TeO_4^{2−}\) are less stable than the conjugate bases \(HSeO_4^−\) and \(SeO_4^{2−}\) because Te is less electronegative then Se. The lower stability of the conjugate base results in lower values for \(K_{a1}\) and \(K_{a2}\), which indicates that \(H_2TeO_4\) is the weaker acid.
Question
Lewis diagrams of the weak bases \(NH_3\) and \(NF_3\) are shown above. Based on these diagrams, which of the following predictions of their relative base strength is correct, and why?
A \(NF_3\) is a stronger base than \(NH_3\) because more than one resonance structure exists for its conjugate acid NF3H+, making it more stable than \(NH^{4+}\).
B \(NF_3\) is a stronger base than \(NH_3\) because of the greater electronegativity of F compared with H.
C \(NF_3\) is a weaker base than \(NH_3\) because of the greater electronegativity of F compared with H.
D \(NF_3\) is a weaker base than \(NH_3\)because more than one resonance structure exists for its conjugate acid \(NF_3H^+\), making it more stable than \(NH_4^+\).
▶️Answer/Explanation
Ans:C
\(NF_3\) is a weaker base because the large electronegativity of the F atom results in \(NF_3\) being a poorer acceptor of protons than \(NH_3\) is.
Question
Which one of the following cannot act as a Lewis base?
A) \(NH_3\) B) \(BF_3\) C) \(Cl^-\) D) \(CN^-\) E) \(H_2O\)
▶️Answer/Explanation
Ans: B
