Question

Circle the molecule or ion that fits the category in each example below and then write the reason (resonance, inductive, periodic trend) on the line provided.

a) Stronger Lewis Base
NH3 or N(CH3)3
b) Stronger Bronsted Acid
HClO4 or HClO
c) Softer Base
NH3 or PH3
d) Harder Lewis Acid
Fe3+ or Fe2+
e) More Soluble Compound
KBr or KF
f) Larger pKa
H2O or CH3OH

Answer 1

NH3 is stronger than N(CH3)3 as a Lewis base. HClO4 is stronger than HClO as a Bronsted acid. NH3 is softer than PH3 as a base. Fe3+ is harder than Fe2+ as a Lewis acid. KBr is more soluble than KF. CH3OH has a larger pKa value than H2O.

Step-by-step explanation:

(a) The stronger Lewis base is NH3 because it can donate a lone pair of electrons to form a coordinate bond with a Lewis acid. N(CH3)3 cannot donate a lone pair of electrons as easily as NH3, so it is a weaker Lewis base.

(b) The stronger Bronsted acid is HClO4 because it has a larger Kₐ value compared to HClO. Kₐ represents the acidity of an acid, and a larger Kₐ value indicates a stronger acid.

(c) The softer base is NH3 because it contains a larger and more polarizable atom (nitrogen) compared to PH3 (phosphorus).

(d) The harder Lewis acid is Fe3+ because it has a higher positive charge compared to Fe2+. A higher positive charge makes an ion more likely to accept a lone pair of electrons.

(e) The more soluble compound is KBr because it forms a stronger ionic bond compared to KF.

(f) The larger pKa value is for CH3OH because it is a weaker acid compared to H2O. A larger pKa value indicates a weaker acid.