MU #1 There are alternate acid-base theories. One theory states that an acid is an H⁺ donor and a base is an H⁺ acceptor.

Example

Consider the following reaction at equilibrium HCl + H₂O <--> H₃O⁺ + Cl^-

In the forward reaction (from left to right) HCl + H₂O --> H₃O⁺ + Cl^-

HCl donates an H⁺ to H₂O therefore HCl is an acid and H₂O is a base since it accepts an H⁺

In the reverse reaction (from right to left) H₃O⁺ + Cl^- --> HCl + H₂O

H₃O⁺ donates an H⁺ to Cl^- therefore H₃O⁺ is an acid and Cl^- is a base since it accepts an H⁺

Problems

Identify the acids and bases in the forward and reverse reactions for the following reactions

HNO₂ + F^- <--> HF + NO₂^-

HSO₄^- + H₂O <--> H₃O⁺ + SO₄^2-  

NH₃ + H₂O <--> NH₄⁺ + OH^-

TEST YOUR UNDERSTANDING

1. In the reaction HNO₃ + H₂O <---> H₃O⁺ + NO₃^- the two acids are

            1. H₂O and HNO₃        2. H₂O and NO₃^-          3. H₂O and H₃O⁺         4. HNO₃ and H₃O⁺

2. Given the reaction: CH₃COOH(aq) + H₂O(l) <---> CH₃COO^-(aq) + H₃O⁺(aq) In this reaction, which substances are bases?

            1. CH₃COOH(ag) and H₂O(l)   2. CH₃COOH(aq) and CH₃COO^-(aq)  3. H₂O(l) and H₃O⁺(aq)    4. H₂O(l) and CH₃COO^-(aq)

3. Given the reaction, HSO₄^-(aq) + NH₃(g) <---> NH₄⁺(aq) + SO₄^2-(aq) , which statement best describes the action of NH₃(g) in the reaction?

            1. It acts as a base, because it is a proton acceptor.       3. It acts as an acid, because it is a proton acceptor.

            2. It acts as a base, because it is a proton donor.           4. It acts as an acid, because it is a proton donor.

4. Given the reaction, HI(g) + H₂O(l) <--> H₃O⁺(aq) + I^-(aq). Which species represents the base in the forward reaction?

            1. HI (g)           2. H₂O (l)         3. H₃O⁺ (aq)       4. I^- (aq)

5. According to the alternate theory, an acid is any species that can

               1. donate a proton        2. donate an electron    3. accept a proton        4. accept an electron

6. In which reaction is water acting only as a base?

            (1) H₂SO₄(aq) + H₂O(l) <--> HSO₄^-(aq) + H₃O⁺(aq)    (3) CH₃COO^-(aq) + H₂O(l) <--> CH₃COOH(aq) + OH^-(aq)

            (2) NH₃(g) + H₂O(l) <--> NH₄⁺(aq) + OH^-(aq)     (4) H₂O(l) + H₂O(l) <--> H₃O⁺(aq) + OH^-(aq)     

7. According to the alternate theory, H₂O is considered to be a base when it

(1) donates an electron             (2) accepts an electron (3) donates a proton     (4) accepts a proton

8. Given the equilibrium system: NH₃(aq) + H₂O(l) <--> NH₄⁺(aq) + OH^-(aq) According to the alternate theory, the H₂O(l) acts as

(1) a base, by receiving a proton           (3) an acid, by receiving a proton

(2) a base, by donating a proton            (4) an acid, by donating a proton

9. Given the reaction: H₂O + HCl <--> H₃O⁺ + Cl^- The base for the forward reaction is (1) H₂O            (2) HCl            (3) H₃O⁺          (4) Cl^-

10. In the reaction NH₃ + HCl --> NH₄⁺  + Cl^-, the NH₃ acts as

                (1) an acid, only    (2) a base, only       (3)  both an acid and a  base (4)  neither an  acid nor a  base

6/07

26 According to one acid-base theory, a water molecule acts as an acid when the water molecule (1) accepts an H⁺ (2) accepts an OH^–    (3) donates an H⁺    (4) donates an OH^–

1/05

27 Given the reaction: NH₃ + HCl → NH₄Cl In this reaction, ammonia molecules (NH₃) act as a base because they

          (1) accept hydrogen ions (H⁺) (2) accept hydroxide ions (OH^–) (3) donate hydrogen ions (H⁺) (4) donate hydroxide ions (OH^–)

1/06

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