Section 10.3 Worksheet PDF

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Water: Both an Acid and a Base Learning Objectives 

Write chemical equations for water acting as an acid and a base.

1. Explain how water can act as an acid. 2. Explain how water can act as a base. 3. Identify water as either a Bronsted-Lowry acid or a Bronsted-Lowry base. a. HCOOH (aq) + H2O (l) → H3O+ (aq) + HCOO- (aq) b. H2O (l) + PO43- (aq) → OH- (aq) + HPO42- (aq) 4. Is H2O(l) acting as an acid or a base? H2O(l) + NH4+(aq) → H3O+(aq) + NH3(aq) 5. Is H2O(l) acting as an acid or a base? H2O(l) + CH3-(aq) → OH-(aq) + CH4(aq) 6. In the aqueous solutions of some salts, one of the ions from the salt can react with water molecules. In some C2H3O2- solutions, the following reaction can occur: C2H3O2- (aq) + H2O (l) → HC2H3O2 (aq) + OH-(aq) Is H2O acting as an acid or a base in this reaction? 7. In the aqueous solutions of some salts, one of the ions from the salt can react with water molecules. In some NH4+ solutions, the following reaction can occur: NH4+ (aq) + H2O(l) → NH3(aq) + H3O+(aq) Is H2O acting as an acid or a base in this reaction? 8. Why is pure water considered neutral?

ANSWER KEY 1. Under the right conditions, H2O can donate a proton, making it a BrønstedLowry acid. 2. Under the right conditions, H2O can accept a proton, making it a BrønstedLowry base. 3. a. H2O acts as the proton acceptor (Brønsted-Lowry base) b. H2O acts as the proton donor (Brønsted-Lowry acid) 4. base 5. acid 6. acid 7. base 8. When water ionizes, equal amounts of H+ (acid) and OH- (base) are formed, so the solution is neither acidic or basic: H2O(l) → H+(aq) + OH(aq) [Side note: It is rare to truly have pure water. Water exposed to air will usually be slightly acidic because dissolved carbon dioxide gas, or carbonic acid, decreases the pH slightly below 7. Alternatively, dissolved minerals, like calcium carbonate (limestone), can make water slightly basic.]...