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Difficulty: HardDefinitions and Theories of Acids and Bases

Match each chemical species or system on the left with its correct theoretical acid-base role or behavior on the right according to the Arrhenius, Brønsted-Lowry, or Lewis concepts.

  • BF3BF_3 in the adduct formation BF3+:NH3→F3B:NH3BF_3 + :NH_3 \rightarrow F_3B:NH_3Lewis acid acting as an electron-pair acceptor due to an incomplete octet
  • HSO4−HSO_4^- when reacting with water to form H3O+H_3O^+ and SO42−SO_4^{2-}Brønsted-Lowry acid acting as a proton donor to produce a hydronium ion
  • HCO3−HCO_3^- in an aqueous system acting in either direction to form H2CO3H_2CO_3 or CO32−CO_3^{2-}Amphoteric (amphiprotic) species capable of both accepting and donating a proton
  • NH2−NH_2^- formed during the auto-ionization of liquid ammonia (2NH3⇌NH4++NH2−2NH_3 \rightleftharpoons NH_4^+ + NH_2^-)Conjugate base formed by solvent self-ionization in non-aqueous acid-base systems

Answer

The correct pairings are: BF3BF_3 matches Lewis acid (electron-pair acceptor); HSO4−HSO_4^- acting to produce H3O+H_3O^+ matches Brønsted-Lowry acid (proton donor); HCO3−HCO_3^- matches amphoteric/amphiprotic species; and NH2−NH_2^- from liquid ammonia matches conjugate base in a non-aqueous solvent system.
Each species is correctly categorized based on fundamental acid-base definitions: Lewis theory accounts for electron-pair transfer (BF3BF_3), Brønsted-Lowry theory accounts for proton donor/acceptor roles (HSO4−HSO_4^- and HCO3−HCO_3^-), and solvent self-ionization describes non-aqueous acid-base equilibria (NH2−NH_2^- in liquid NH3NH_3).

Step-by-Step Solution

1
Analyze BF3BF_3 in BF3+:NH3→F3B:NH3BF_3 + :NH_3 \rightarrow F_3B:NH_3
Boron has six valence electrons and accepts an electron pair from nitrogen.
According to Lewis theory, an electron-pair acceptor is defined as a Lewis acid.
2
Analyze HSO4−HSO_4^- converting to SO42−SO_4^{2-} in water
HSO4−HSO_4^- transfers a proton (H+H^+) to H2OH_2O to form H3O+H_3O^+.
According to Brønsted-Lowry theory, a proton donor is an acid.
3
Analyze HCO3−HCO_3^- double-behavior in water
HCO3−HCO_3^- can accept H+H^+ to become H2CO3H_2CO_3 or donate H+H^+ to become CO32−CO_3^{2-}.
Species that can act as either a proton donor or proton acceptor are termed amphiprotic/amphoteric.
4
Analyze NH2−NH_2^- in liquid ammonia auto-ionization
Ammonia undergoes auto-protolysis: 2NH3⇌NH4++NH2−2NH_3 \rightleftharpoons NH_4^+ + NH_2^-.
The amide ion (NH2−NH_2^-) is formed when NH3NH_3 loses a proton, acting as the characteristic conjugate base of the liquid ammonia solvent system.

Key Concept

Distinction and application of Arrhenius, Brønsted-Lowry, Lewis, and solvent-system theories of acids and bases.
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Topics

Definitions and Theories of Acids and Bases

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