HW #34

Bronsted-Lowry acids/bases

The Brønsted–Lowry Theory: defines acids and bases as either proton donors or proton acceptors

According to the theory:

  • a Brønsted–Lowry acid donates a proton (is a proton donor)

  • a Brønsted–Lowry base accepts a proton (is a proton acceptor)

  • A lot of reactions in life involve the transfer of protons from substances called acids to substances called bases

EX: When hydrogen chloride gas dissolves in water, it donates a proton (H+) to the water molecule, which accepts the proton.

The reaction between hydrogen chloride gas and water:

  • The hydrogen chloride gas acts as a Brønsted–Lowry acid and the water molecule as a Brønsted–Lowry base

  • The solution formed is named hydrochloric acid and is an example of a Brønsted–Lowry acid


Three common types of acid:

  • binary acids

  • oxyacids

  • organic acids

  • Binary acids are formed when a halide reacts with hydrogen (HF, HBr, HCl, etc.)

  • Oxyacids acids are derived from polyatomic ions (HNO3(aq), H2SO4(aq), H2CO3(aq), etc)

  • Organic acids contain a carboxyl group (Ethanoic acid: CH3COOH(aq) & Benzoic Acid: C6H5COOH(s))

  • Acids can be classified as monoprotic, diprotic, or triprotic depending on the number of hydrogen ions or protons that they can donate in an acid-base reaction

Name of base Formula

Calcium oxide CaO(s)

Copper(II) oxide CuO(s)

Sodium hydroxide NaOH(aq)

Lithium hydroxide LiOH(aq)

Calcium hydroxide Ca(OH)2(aq)

Barium hydroxide Ba(OH)2(aq)

  • Carbonates and metal hydrogen carbonates are also examples of weak bases

  • Ammonia, amines and amides are also examples of weak bases

  • Hydrochloric acid and nitric acid are monoprotic acids

  • Sulfuric acid is an example of a diprotic acid

  • Phosphoric acid is an example of a triprotic acid

Conjugate Acids & Bases

  • The reaction between ammonia and water to produce the ammonium ion and the hydroxide ion is:

    • NH3(g) + H2O(l) ⇌ NH4+(aq) + OH−(aq)

  • In the forward reaction, water acts as a Brønsted–Lowry acid and ammonia as a Brønsted–Lowry base

  • it’s a reversible reaction (as indicated by the two-way arrow) —> forward reaction occurs at the same rate as the reversible reaction & the reaction is at equilibrium

  • In the reverse reaction: NH4+ ion donates a proton to the OH− ion —> the NH4+ ion is acting as a B–L acid and the OH− ion is acting as a B–L base

Conjugate (Acid-Base) Pair: differ by one proton (EX: NH3 & NH4+) (EX: H2O & OH-)

Amphiprotic: species that can act as either B-L acid or base (EX: Water)

  • water in the reaction with ammonia behaves as an acid and donates the proton

  • water in the reaction with HCl gas behaves as a base and accepts the proton

  • HSO4- is also an example