Chapter 11 – Acids and Bases – Practice Problems Section 11.1 – Acids and Bases Goal: Describe and name acids and bases. Summary: An Arrhenius acid produces H+ and an Arrhenius base produces OH- in aqueous solutions. Acids taste sour, may sting, and neutralize bases. Bases taste bitter, feel slippery, and neutralize acids. Naming acids: Binary acids contain a single anion: HnX. To name: hydro [anion with -ic end] acid HBr – hydrobromic acid H2S – hydrosulfuric acid Polyatomic acids contain a polyatomic ion: HnXOm (XOm = polyatomic ion) [polyatomic ion] acid if the polyatomic ion ends in -ate change to -ic if the polyatomic ion ends in -ite change to -ous H2SO4 (sulfate) – sulfuric acid H2SO3 (sulfite) – sulfous acid Practice Problems 1. Indicate whether each of the following statements is characteristic of an Arrhenius acid, Arrhenius base, or both: a. has a sour taste b. neutralizes bases c. produces H+ ions in water d. is named barium hydroxide e. is an electrolyte 2. Indicate whether each of the following statements is characteristics of an Arrhenius acid, Arrhenius base, or both: a. neutralizes acids b. produces OH- ions in water c. has a slippery feel d. conducts an electrical current in solution 3. Identify each of the following as an Arrhenius acid, Arrhenius base, or none: b. CsOH c. Mg(NO3)2 d. HClO4 e. HNO2 f. MgBr2 g. NH3 h. Li2SO3 4. Name each of the following acids or bases: a. HCl b. Ca(OH)2 c. HClO4 d. HNO3 e. H2SO3 5. Name each of the following acids or bases: a. Al(OH)3 b. H2SO4 c. HBr d. KOH e. HNO2 f. HClO2 6. Write formulas for each of the following acids or bases: a. rubidium hydroxide b. hydrofluoric acid c. phosphoric acid d. lithium hydroxide e. ammonium hydroxide 7. Write formulas for each of the following acids or bases: a. barium hydroxide b. hydroiodic acid c. nitric acid d. acetic acid e. hypochlorous acid Section 11.2 – Bronsted-Lowery Acids Goal: Identify conjugate acid-base pairs for Bronsted-Lowry acids and bases. Summary: A Bronsted-Lowry acid donates H+ and a Bronsted-Lowry base accepts H+. Identifying Conjugate Acid-Base Pairs • According to Bronsted-Lowry theory, a conjugate acid-base pair consists of molecules or ions related by the loss of one H+ by an acid, an the gain of one H+ by a base. • Every acid-base reaction contains two conjugate acid-base pairs because an H+ is transferred in both the forward and reverse directions. When an acid such as HF loses one H+, the conjugate base F- is formed. + + When H2O acts as a base, it gains one H , which forms its conjugate acid, H3O . Practice Problems 8. Write the formula for the conjugate base for each of the following acids: - a. HCO3 2- b. HPO4 c. HBrO 9. Write the formula for the conjugate acid for each of the following bases: 2- a. CO3 b. H2O - c. H2PO4 10. In the following reaction, the acid-conjugate base pair is __i__ and the base-conjugate acid pair is __ii__. - + H3PO4(aq) + H2O(l) H2PO4 (aq) + H3O (aq) + - a. (i) H3PO4/H3O (ii) H2O/H2PO4 - + b. (i) H3PO4/H2O (ii) H2PO4 /H3O + - c. (i) H2O/H3O (ii) H3PO4/H2PO4 - + d. (i) H2O/H2PO4 (ii) H3PO4/H3O - + e. (i) H3PO4/H2PO4 (ii) H2O/H3O 11. In the following reaction, the acid-conjugate base pair is __i__ and the base-conjugate acid pair is __ii__. 2- - - CO3 (aq) + H2O(l) HCO3 (aq) + OH (aq) 2- - - a. (i) CO3 / H2O (ii) HCO3 /OH - 2- - b. (i) H2O/HCO3 (ii) CO3 /OH - 2- - c. (i) H2O/OH (ii) CO3 /HCO3 2- - - d. (i) CO3 /OH (ii) H2O/HCO3 2- - - e. (i) CO3 /HCO3 (ii) H2O/OH 12. In the following reaction, the acid-conjugate base pair is __i__ and the base-conjugate acid pair is __ii__. - + H3PO4(aq) + NH3(aq) H2PO4 (aq) + NH4 (aq) - + a. (i) H3PO4/H2PO4 (ii) NH3/NH4 + - b. (i) H3PO4/NH4 (ii) NH3/H2PO4 - + c. (i) H3PO4/NH3 (ii) H2PO4 /NH4 - + d. (i) H2PO4 /H3PO4 (ii) NH4 /NH3 + - e. (i) NH3/NH4 (ii) H3PO4/H2PO4 13. Complete the following table: Acid Conjugate Base HI Cl- + NH4 HS- 14. Complete the following table: Base Conjugate Acid F- HC2H3O2 - HSO3 ClO- + + 15. When ammonium chloride dissolves in water, the ammonium ion NH4 donates an H to water. Write a balanced equation for the reaction of the ammonium ion with water. + + a. NH4 + H2O NH3 + H3O + + + b. NH4 + H3O NH3 + H2O + H + + - c. NH4 + H3O NH3 + H2O + OH - + d. NH3 + H2O NH2 + H3O + + e. NH3 + H3O NH4 + H2O 2- 16. When sodium carbonate dissolves in water, the carbonate ion CO3 acts as a base. Write a balanced equation for the reaction of the carbonate ion with water. 2- + a. CO3 + H2O CO2 + H3O 2- - - b. CO3 + H2O HCO3 + OH 2- c. CO3 + H2O H2CO4 2- - 2- d. CO3 + OH CO3 + H2O 2- e. CO3 + H2O H2CO3 Section 11.3 – Strengths of Acids and Bases Goal: Write equations for the dissociation of strong and weak acids; identify the direction of reaction. Summary: + Strong acids dissociate completely in water, and the H is accepted by H2O acting as a base. + - HCl + H2O H3O + Cl A weak acid dissociates only slightly in water, producing only a small amount of H+ and therefore a small + amount of H3O + - HI + H2O H3O + I Strong bases are hydroxides with metals from Groups 1 and 2 and dissociate completely in water. (NaOH, Ca(OH)2, …) An important weak base is ammonia, NH3. Understanding the Concepts: In diagrams A and B, determine if the diagram represents a strong acid or a weak acid. The acid has the formula HX. Practice Problems 17. Using Table 11.3, identify the stronger acid in each of the following pairs: + + a. NH4 or H3O b. H2SO4 or HCl c. H2O or H2CO3 18. Using Table 11.3, identify the weaker acid in each of the following pairs: - a. HCl or HSO4 b. HNO2 or HF - + c. HCO3 or NH4 19. Predict whether the following reaction contains mostly reactants or products at equilibrium: - + H2CO3(aq) + H2O(l) HCO3 (aq) + H3O (aq) a. mostly products b. mostly reactants 20. Predict whether the following reaction contains mostly reactants or products at equilibrium: + + NH4 (aq) + H2O(l) NH3(aq) + H3O (aq) a. mostly products b. mostly reactants 21. Predict whether the following reaction contains mostly reactants or products at equilibrium: - + HNO2(aq) + NH3(aq) NO2 (aq) + NH4 (aq) a. mostly products b. mostly reactants 22. Predict whether the following reaction contains mostly reactants or products at equilibrium: + - H3PO4(aq) + H2O(l) H3O (aq) + H2PO4 (aq) a. mostly products b. mostly reactants Challenge Problems 23. a. Write the formula for the conjugate base of H2S b. Write the formula for the conjugate base of H3PO4 c. Which is the weaker acid: H2S or H3PO4? - 24. a. Write the formula for the conjugate base of HCO3 b. Write the formula for the conjugate base of HC2H3O2 - c. Which is the stronger acid: HCO3 or HC2H3O2? Section 11.4 – Dissociation Constants for Acids and Bases Goal: Write the expression for the dissociation constant of a weak acid or weak base. Summary: In water, weak acids and weak bases produce only a few ions when equilibrium is reached. Weak acids have small Ka values, whereas strong acids, which are essentially 100% dissociated, have very large Ka values. + - The reaction for a weak acid can be written as HA + H2O H3O + A . The acid dissociation constant expression is written as + − [H3O ][A ] Ka = [HA] + - For a weak base the equation is B + H2O BH + OH , and the base dissociation constant expression is written as [BH+][OH−] Kb = [B] Practice Problems 25. Answer true or false for each of the following: A strong acid… a. is completely dissociated in aqueous solution b. has a small value of Ka c. has a strong conjugate base d. has a weak conjugate base e. is slightly dissociated in aqueous solution 26. Answer true or false for each of the following: A weak acid… a. is completely dissociated in aqueous solution b. has a small value of Ka c. has a strong conjugate base d. has a weak conjugate base e. is slightly dissociated in aqueous solution 27. Consider the following acids and their dissociation constants: + - -2 H2SO3(aq) + H2O(l) H3O (aq) + HSO3 (aq) Ka = 1.2 x 10 - + 2- -19 HS (aq) + H2O(l) H3O (aq) + S (aq) Ka = 1.3 x 10 - a. Which is the stronger acid, H2SO3 or HS ? b. What is the conjugate base of H2SO3? c. Which acid has the weaker conjugate base? d. Which acid has the stronger conjugate base? e. Which acid produces more ions? 28. Consider the following acids and their dissociation constants: 2- + 3- -13 HPO4 (aq) + H2O(l) H3O (aq) + PO4 (aq) Ka = 2.2 x 10 + - -4 HCHO2(aq) + H2O(l) H3O (aq) + CHO2 (aq) Ka = 1.8 x 10 2- a. Which is the weaker acid, HPO4 or HCHO2? 2- b. What is the conjugate base of HPO4 ? c. Which acid has the weaker conjugate base? d. Which acid has the stronger conjugate base? e. Which acid produces more ions? -10 + 29. Aniline, C6H5NH2, a weak base with a Kb of 4.0 x 10 , reacts with water to form C6H5NH3 and hydroxide ion. Write the equation for the reaction and the base dissociation constant expression for aniline. Section 11.5 – Dissociation of Water + - Goal: Use the water dissociation constant expression to calculate the [H3O ] and [OH ] in an aqueous solution. Summary: • In pure water, a few water molecules transfer H+ to other water molecules, + - producing small, but equal amounts of [H3O ] and [OH ].