10.1: Arrhenius Definition of Acids and Bases Concept Review Exercises Give the Arrhenius definitions of an acid and a base. What is neutralization? Answers Arrhenius acid: a compound that increases the concentration of hydrogen ion (H + ) in aqueous solution; Arrhenius base: a compound that increases the concentration of hydroxide ion (OH − ) in aqueous solution. the reaction of an acid and a base Exercises Give two examples of Arrhenius acids. Give two examples of Arrhenius bases. List the general properties of acids. List the general properties of bases. Name each compound. (For acids, look up the name in Table 10.1.1. For bases, use the rules for naming ionic compounds from Chapter 3.) a. HBr(aq) b. Ca(OH) 2 (aq) c. HNO 3 (aq) d. Fe(OH) 3 (aq) 6. Name each compound. a. HI(aq) b. Cu(OH) 2 (aq) c. H 3 PO 4 (aq) d. CsOH(aq) 7. Write a balanced chemical equation for the neutralization of Ba(OH) 2 (aq) with HNO 3 (aq). 8. Write a balanced chemical equation for the neutralization of H 2 SO 4 (aq) with Cr(OH) 3 (aq). 9. Gastric juice, the digestive fluid produced in the stomach, contains hydrochloric acid, HCl . Milk of Magnesia, a suspension of solid Mg(OH) 2 in an aqueous medium, is sometimes used to neutralize excess stomach acid. Write a complete balanced equation for the neutralization reaction. 10. Identify the salt produced in each acid-base reaction below. Then, balance the equation. a. 2HCl + Sr(OH) 2 → 2H 2 O + ?? b. KNO 3 ; HNO 3 + KOH → ?? + H 2 O c. HF + Ca(OH) 2 ---> ?? + H 2 O 11. How many moles of sodium hydroxide (NaOH) are needed to neutralize 0.844 mol of acetic acid (HC 2 H 3 O 2 )? (Hint: begin by writing a balanced chemical equation for the process.) 12. How many moles of perchloric acid (HClO 4 ) are needed to neutralize 0.052 mol of calcium hydroxide [Ca(OH) 2 ]? (Hint: begin by writing a balanced chemical equation for the process 13. Hydrazoic acid (HN 3 ) can be neutralized by a base. a. Write the balanced chemical equation for the reaction between hydrazoic acid and calcium hydroxide. b. How many milliliters of 0.0245 M Ca(OH) 2 are needed to neutralize 0.564 g of HN 3 ? 14. Citric acid (H 3 C 6 H 5 O 7 ) has three hydrogen atoms that can form hydrogen ions in solution. a. Write the balanced chemical equation for the reaction between citric acid and sodium hydroxide. b. If an orange contains 0.0675 g of H 3 C 6 H 5 O 7 , how many milliliters of 0.00332 M NaOH solution are needed to neutralize the acid? 15. Magnesium hydroxide [Mg(OH) 2 ] is an ingredient in some antacids. How many grams of Mg(OH) 2 are needed to neutralize the acid in 158 mL of 0.106 M HCl(aq)? It might help to write the balanced chemical equation first. 16. Aluminum hydroxide [Al(OH) 3 ] is an ingredient in some antacids. How many grams of Al(OH) 3 are needed to neutralize the acid in 96.5 mL of 0.556 M H 2 SO 4 (aq)? It might help to write the balanced chemical equation first. 17. Write the balanced chemical equation for the reaction between HBr and Ca(OH) 2 . What volume of 0.010 M HBr solution is be required to neutralize 25 mL of a 0.0100 M Ca(OH) 2 solution? 18. Write the balanced chemical equation for the reaction between HNO 3 and KOH . What volume of 0.5M HNO 3 is required to neutralize 60 mL of 0.4M KOH solution? Answers HCl and HNO 3 (answers will vary) NaOH and Ca(OH) 2 (answers will vary) sour taste, react with metals, react with bases, and turn litmus red bitter taste, feels slippery, react with acids and turn litmus blue a. hydrobromic acid b. calcium hydroxide c. nitric acid d. iron(III) hydroxide 6. a. hydroiodic acid b. cupric hydroxide c. phosphoric acid d. cesium hydroxide 7. 2HNO 3 (aq) + Ba(OH) 2 (aq) → Ba(NO 3 ) 2 (aq) + 2H 2 O 8. 3H 2 SO 4 (aq) + 2Cr(OH) 3 (aq) → Cr 2 (SO 4 ) 3 (aq) + 6H 2 O 9. Mg(OH) 2 + 2HCl --> MgCl 2 + 2H 2 O 10. a. SrCl 2 ; 2HCl + Sr(OH) 2 → 2H 2 O + SrCl 2 b. KNO 3 ; HNO 3 + KOH → KNO 3 + H 2 O c. CaF 2 ; 2HF + Ca(OH) 2 → CaF 2 + 2H 2 O 11. 0.844 mol 12. 0.104 mol 13. Part 1: 2HN 3 (aq) + Ca(OH) 2 → Ca(N 3 ) 2 + 2H 2 O Part 2: 268 mL 14. Part 1: H 3 C 6 H 5 O 7 (aq) + 3NaOH(aq) → Na 3 C 6 H 5 O 7 (aq) + 3H 2 O Part 2: 317.5 mL 15. 0.488 g 16. 2.79 g 17. 2HBr + Ca(OH) 2 → CaBr 2 + 2H 2 O ; 50 mL HBr 18. HNO 3 + KOH → KNO 3 + H 2 O ; 48 mL HNO 3 10.2: Brønsted-Lowry Definition of Acids and Bases Concept Review Exercise Give the definitions of a Brønsted-Lowry acid and a Brønsted-Lowry base. Answer A Brønsted-Lowry acid is a proton donor, while a Brønsted-Lowry base is a proton acceptor. Exercises Label each reactant as a Brønsted-Lowry acid or a Brønsted-Lowry base. HCl(aq) + NH 3 (aq) → NH 4 + (aq) + Cl − (aq) Label each reactant as a Brønsted-Lowry acid or a Brønsted-Lowry base. H 2 O(ℓ) + N 2 H 4 (aq) → N 2 H 5 + (aq) + OH − (aq) Explain why a Brønsted-Lowry acid can be called a proton donor. Explain why a Brønsted-Lowry base can be called a proton acceptor. Write the chemical equation of the reaction of ammonia in water and label the Brønsted-Lowry acid and base. Write the chemical equation of the reaction of methylamine (CH 3 NH 2 ) in water and label the Brønsted-Lowry acid and base. Demonstrate that the dissolution of HNO 3 in water is actually a Brønsted-Lowry acid-base reaction by describing it with a chemical equation and labeling the Brønsted-Lowry acid and base. Identify the Brønsted-Lowry acid and base in the following chemical equation: C 3 H 7 NH 2 (aq) + H 3 O + (aq) → C 3 H 7 NH 3 + (aq) + H 2 O(ℓ) Identify the Brønsted-Lowry acid and the Brønsted-Lowry base in each of the following equations 1. \(\ce{NO2- + H2O ⟶ HNO2 + OH-}\) 2. \(\ce{HBr + H2O ⟶ H3O+ + Br-}\) 3. \(\ce{HS- + H2O ⟶ H2S + OH-}\) 4. \(\ce{H2PO4- + OH- ⟶HPO4^2- + H2O}\) 5. \(\ce{H2PO4- + HCl ⟶ H3PO4 + Cl-}\) 10. Write the chemical equation for the reaction that occurs when cocaine hydrochloride (C 17 H 22 ClNO 4 ) dissolves in water and donates a proton to a water molecule. (When hydrochlorides dissolve in water, they separate into chloride ions and the appropriate cation.) 11. If codeine hydrobromide has the formula C 18 H 22 BrNO 3 , what is the formula of the parent compound codeine? Answers HCl: Brønsted-Lowry acid; NH 3 : Brønsted-Lowry base H 2 O: Brønsted-Lowry acid; N 2 H 4 : Brønsted-Lowry base A Brønsted-Lowry acid gives away an H + ion—nominally, a proton—in an acid-base reaction. A Brønsted-Lowry base accepts an H + ion (a proton) in an acid-base reaction. NH 3 + H 2 O → NH 4 + + OH − (here NH 3 = Brønsted-Lowry base; H 2 O = Brønsted-Lowry acid) CH 3 NH 2 + H 2 O → CH 3 NH 3 + + OH − (here CH 3 NH 2 = Brønsted-Lowry base; H 2 O = Brønsted-Lowry acid) HNO 3 + H 2 O → H 3 O + + NO 3 − (here HNO 3 = Brønsted-Lowry acid; H 2 O = Brønsted-Lowry base) C 3 H 7 NH 2 (aq) + H 3 O + (aq) → C 3 H 7 NH 3 + (aq) + H 2 O(ℓ) (here H 3 O + = Brønsted-Lowry acid; C 3 H 7 NH 2 = Brønsted-Lowry base) 10.3: Water - Both an Acid and a Base Concept Review Exercises Explain how water can act as an acid. Explain how water can act as a base. Answers Under the right conditions, H 2 O can donate a proton, making it a Brønsted-Lowry acid. Under the right conditions, H 2 O can accept a proton, making it a Brønsted-Lowry base. Exercises Is H 2 O(ℓ) acting as an acid or a base? H 2 O(ℓ) + NH 4 + (aq) → H 3 O + (aq) + NH 3 (aq) Is H 2 O(ℓ) acting as an acid or a base? CH 3 − (aq) + H 2 O(ℓ) → CH 4 (aq) + OH − (aq) In the aqueous solutions of some salts, one of the ions from the salt can react with water molecules. In some C 2 H 3 O 2 − solutions, the following reaction can occur: C 2 H 3 O 2 − (aq) + H 2 O(ℓ) → HC 2 H 3 O 2 (aq) + OH − (aq) Is H 2 O acting as an acid or a base in this reaction? In the aqueous solutions of some salts, one of the ions from the salt can react with water molecules. In some NH 4 + solutions, the following reaction can occur: NH 4 + (aq) + H 2 O → NH 3 (aq) + H 3 O + (aq) Is H 2 O acting as an acid or a base in this reaction? Why is pure water considered neutral? Answers base acid acid base 5. When water ionizes, equal amounts of H + (acid) and OH − (base) are formed, so the solution is neither acidic nor basic: H 2 O(ℓ) → H + (aq) + OH − (aq) 10.4: The Strengths of Acids and Bases Concept Review Exercises Explain the difference between a strong acid or base and a weak acid or base. Explain what is occurring when a chemical reaction reaches equilibrium. Define pH . AnswerS A strong acid or base is 100% ionized in aqueous solution; a weak acid or base is less than 100% ionized. The overall reaction progress stops because the reverse process balances out the forward process. pH is a measure of the hydrogen ion concentration. Exercises Name a strong acid and a weak acid. (Hint: use Table 10.4.1.) Name a strong base and a weak base. (Hint: use Table 10.4.1.) Is each compound a strong acid or a weak acid? Assume all are in aqueous solution. (Hint: use Table 10.4.1.) HF HC 2 H 3 O 2 HCl HClO 4 Is each compound a strong acid or a weak acid? Assume all are in aqueous solution. (Hint: use Table 10.4.1.) H 2 SO 4 HSO 4 − HPO 4 2 − HNO 3 Is each compound a strong base or a weak base? Assume all are in aqueous solution. (Hint: use Table 10.4.1.) NH 3 NaOH Mg(OH) 2 Cu(OH) 2 Is each compound a strong base or a weak base? Assume all are in aqueous solution. (Hint: use Table 10.4.1.) KOH H 2 O Fe(OH) 2 Fe(OH) 3 Write the chemical equation for the equilibrium process for each weak acid in Exercise 3. Write the chemical equation for the equilibrium process for each weak acid in Exercise 4. Write the chemical equation for the equilibrium process for each weak base in Exercise 5. Write the chemical equation for the equilibrium process for each weak base in Exercise 6. Which is the stronger acid—HCl(aq) or HF(aq)? Which is the stronger base—KOH(aq) or Ni(OH) 2 (aq)? Consider the two acids in Exercise 11. For solutions that have the same concentration, which one would you expect to have a lower pH? Consider the two bases in Exercise 12. For solutions that have the same concentration, which one would you expect to have a higher pH? Consider the list of substances in Table \PageIndex3\PageIndex3.2"The pH Values of Some Common Solutions". What is the most acidic substance on the list that you have encountered recently? Consider the list of substances in Table \PageIndex3\PageIndex3.2"The pH Values of Some Common Solutions". What is the most basic substance on the list that you have encountered recently? Indicate whether solutions with the following pH values are acidic, basic, or neutral: pH = 9.4 pH = 7.0 pH = 1.2 pH = 6.5 Answers strong acid: HCl; weak acid: HC 2 H 3 O 2 (answers will vary) strong base: NaOH; weak base: NH 3 (answers will vary) weak weak strong strong strong weak weak strong weak strong strong weak strong weak weak weak 7. 3a: HF(aq) ⇆ H + (aq) + F − (aq); 3b: HC 2 H 3 O 2 (aq) ⇆ H + (aq) + C 2 H 3 O 2 − (aq) 8. 4b: HSO 4 − (aq) ⇆ H + (aq) + SO 4 2 − (aq); 4c: HPO 4 2 − (aq) ⇆ H + (aq) + PO 4 3 − (aq) 9. 5a: NH 3 (aq) + H 2 O ⇆ NH 4 + (aq) + OH − (aq); 5d: Cu(OH) 2 (aq) ⇆ Cu 2 + (aq) + 2OH − (aq) 10. 6b: H 2 O + H 2 O ⇆ H 3 O + (aq) + OH − (aq); 6c: Fe(OH) 2 (aq) ⇆ Fe 2 + (aq) + 2OH − (aq); 6d: Fe(OH)3(aq) ⇆ Fe 3 + (aq) + 3OH − (aq) 11. HCl(aq) 12. KOH(aq) 13. HCl(aq) 14. KOH(aq) 15. (answers will vary) 16. (answers will vary) 17. 1. basic 2. neutral 3. acidic (strongly) 4. acidic (mildly) 10.5: Buffers Concept Review Exercise Explain how a buffer prevents large changes in pH. Answer A buffer has components that react with both strong acids and strong bases to resist sudden changes in pH. Exercises Describe a buffer. What two related chemical components are required to make a buffer? Can a buffer be made by combining a strong acid with a strong base? Why or why not? Which solute combinations can make a buffer? Assume all are aqueous solutions. HCl and NaCl HNO 2 and NaNO 2 NH 4 NO 3 and HNO 3 NH 4 NO 3 and NH 3 Which solute combinations can make a buffer? Assume all are aqueous solutions. H 3 PO 4 and Na 3 PO 4 NaHCO 3 and Na 2 CO 3 NaNO 3 and Ca(NO 3 ) 2 HN 3 and NH 3 For each combination in Exercise 3 that is a buffer, write the chemical equations for the reactions of the buffer components when a strong acid and a strong base is added. For each combination in Exercise 4 that is a buffer, write the chemical equations for the reaction of the buffer components when a strong acid and a strong base is added. The complete phosphate buffer system is based on four substances: H 3 PO 4 , H 2 PO 4 − , HPO 4 2 − , and PO 4 3 − . What different buffer solutions can be made from these substances? Explain why NaBr cannot be a component in either an acidic or a basic buffer. Explain why Mg(NO 3 ) 2 cannot be a component in either an acidic or a basic buffer. Answers A buffer resists sudden changes in pH. It has a weak acid or base and a salt of that weak acid or base. No. Combining a strong acid and a strong base will produce salt and water. Excess strong acid or strong base will not act as a buffer. not a buffer buffer not a buffer buffer 4. 1. not a buffer 2. buffer 3. not a buffer 4. not buffer 3b: strong acid: H + + NO 2 − → HNO 2 ; strong base: OH − + HNO 2 → H 2 O + NO 2 − ; 3d: strong acid: H + + NH 3 → NH 4 + ; strong base: OH − + NH 4 + → H 2 O + NH 3 4b: strong acid: H + + CO 3 2 − → HCO3 − ; strong base: OH − + HCO 3 − → H 2 O + CO 3 2 − ; Buffers can be made by combining H 3 PO 4 and H 2 PO 4 − , H 2 PO 4 − and HPO 4 2 − , and HPO 4 2 − and PO 4 3 − . NaBr splits up into two ions in solution, Na + and Br − . Na + will not react with any added base knowing that NaOH is a strong base. Br- will not react with any added acid knowing that HBr is a strong acid. Because NaBr will not react with any added base or acid, it does not resist change in pH and is not a buffer. Mg(NO 3 ) 2 includes two types of ions, Mg 2 + and NO 3 − . Mg(OH) 2 is strong base and completely dissociates (100% falls apart), so Mg 2 + will not react with any added base (0% combines with OH − ). HNO 3 is strong acid and completely dissociates (100% falls apart), so NO 3 − will not react with any added acid (0% combines with H + ). Because Mg(NO 3 ) 2 will not react with any added base or acid, it does not resist change in pH and is not a buffer. Additional Exercises The properties of a 1.0 M HCl solution and a 1.0 M HC 2 H 3 O 2 solution are compared. Measurements show that the hydrochloric acid solution has a higher osmotic pressure than the acetic acid solution. Explain why. Of a 0.50 M HNO 3 solution and a 0.50 M HC 2 H 3 O 2 solution, which should have the higher boiling point? Explain why. The reaction of sulfuric acid [H 2 SO 4 (aq)] with sodium hydroxide [NaOH(aq)] can be represented by two separate steps, with only one hydrogen ion reacting in each step. Write the chemical equation for each step. The reaction of aluminum hydroxide [Al(OH) 3 (aq)] with hydrochloric acid [HCl(aq)] can be represented by three separate steps, with only one hydroxide ion reacting in each step. Write the chemical equation for each step. A friend brings you a small sample of an unknown chemical. Assuming that the chemical is soluble in water, how would you determine if the chemical is an acid or a base? A neutral solution has a hydrogen ion concentration of about 1 × 10 −7 M. What is the concentration of the hydroxide ion in a neutral solution? The Lewis definitions of an acid and a base are based on electron pairs, not protons. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. Use Lewis diagrams to show that H + (aq) + OH − (aq) → H 2 O(ℓ) is an acid-base reaction in the Lewis sense as well as in the Arrhenius and Brønsted-Lowry senses. Given the chemical reaction NH 3 (g) + BF 3 (g) → NH 3 —BF 3 (s) show that the reaction illustrated by this equation is an acid-base reaction if we use the Lewis definitions of an acid and a base (see Exercise 7). The product contains a bond between the N and B atoms. Answers HCl is a strong acid and yields more ions in solution. HC 2 H 3 O 2 is a weak acid and undergoes partial ionization in solution. HNO 3 is a strong acid while HC 2 H 3 O 2 is a weak acid. HNO 3 dissociates 100% and its solution contains more ions. The more ions the solution contains the lower is its vapor pressure; the higher temperature is required for it to boil. H 2 SO 4 + NaOH → NaHSO 4 + H 2 O; NaHSO 4 + NaOH → Na 2 SO 4 + H 2 O Al(OH) 3 + HCl → Al(OH) 2 Cl + H 2 O; Al(OH) 2 Cl + HCl → Al(OH)Cl 2 + H 2 O; Al(OH)Cl 2 + HCl → AlCl3 + H 2 O One way is to add it to NaHCO 3 ; if it bubbles, it is an acid. Alternatively, add the sample to litmus and look for a characteristic color change (red for acid, blue for base). In a neutral solution, [OH - ] = [H + ] = 1.0 x 10 -7 M The O atom is donating an electron pair to the H + ion, making the base an electron pair donor and the acid an electron pair acceptor. The N atom is donating a lone pair to B in BF 3 , Hence NH 3 is the Lewis base and BF 3 is the Lewis acid.