Honors Chemistry Ka, Kb and Neutralization Rxns. 1. Describe the difference between a weak acid and a strong acid. Give an example of each. ο· weak acids partially ionizes in solution, whereas strong acids completely ionize in solution. Weak acid: HC2H3O2 (acetic acid), H2S (hydrosulfic acid). Strong acid: HNO3 (nitric acid), HCl (hydrochloric acid.) 2. Describe the difference between a weak base and a strong base. Give an example of each. ο· weak base partially dissociates in solution and a strong base completely dissociates in solution. Weak base: NH3 ( ammonia), HCO3- (bicarbonate). Strong base: NaOH (sodium hydroxide), KOH (potassium hydroxide.) 3. Define the symbol Ka and Kb. ο· Ka is the acid ionization constant and it is the ratio of the concentrations of the products divided by the [π»+][π΄−] reactants for an acid. If Ka>1 then it is a strong acid and < 1 a weak acid. πΎπ = [π»π΄} . Kb is the equivalent relationship for bases. 4. The concentration H+ in a HF acid solution is 1.0 x 10-4 M and the amount of undissociated (not ionized) Hydroflouric Acid, HF, is 2.5 x 10-6 M. What is the dissociation constant for this acid? Is this considered to be a strong or weak acid? ο· + − π»πΉ(π) βΆ π»(ππ) + πΉ(ππ) πΎπ = [π»+][π΄−] (1 π₯ 10−4 )(1 π₯ 10−4 ) [π»π΄} 2.5 π₯10−6 = = .004 therefore weak acid 5. Acetic Acid is the conjugate acid of the acetate anion. It is a weak monoprotic acid that dissociates to an acetate ion and a hydrogen ion in aqueous solution. Calculate Ka for acetic acid if a 1.0 M solution results in an equilibrium [H+] =0.0042 M. ο· + π»πΆ2 π»3 π2 βΆ π»(ππ) + πΆ2 π»3 π2 − (ππ) πΎπ = [π»+][π΄−] (.0042).0042) [π»π΄} 1.0 = = 1.76 π₯ 10−5 therefore weak acid 6. Ammonia is a weak base. If the initial concentration of ammonia is 0.150 M and the equilibrium concentration of OH- is 1.6 x 10-3 M, calculate Kb for ammonia. ο· − ππ»3 βΆ ππ»4 + (ππ) + ππ»(ππ) πΎπ = [ππ»−][π»π΅+] (1.6 π₯ 10−3 )(1.6 π₯ 10−3 ) [π»π΅] 0.150 = = 1.71 π₯ 10−5 therefore weak base 7. At 37°C, which is normal body temperature, Kw = 2.4 x 10-14. Calculate [H+] and [OH-] in a neutral solution at this temperature. ο· πΎπ€ = [π» +][ππ»−] 2.4 x 10-14 = [H+][OH-] 2.4 x 10-14 = x2 = 1.55 x 10-7 M 8. At 50°C, Kw = 5.47 x 10-14. Calculate [H+] and [OH-] in a neutral solution at this temperature. ο· πΎπ€ = [π» +][ππ»−] 5.47 x 10-14 = [H+][OH-] 5.47 x 10-14 = x2 = 2.34 x 10-7 M 9. A 0.010 M solution of aspirin, a weak monoprotic acid, has a pH of 3.3. What is the Ka of aspirin? ο· ππ» = − log[π» + ] 3.3 = −log[π» + ] 10−3.3 = 5.01 π₯ 10−4 π πΎπ = (5.01 π₯ 10−4 )(5.01 π₯ 10−4 ) 0.010 = 2.51 π₯ 10−5 10. A 0.513 M solution of a weak base has a pH of 11.4. What is the Kb of the base? ο· ππ» + πππ» = 14 πππ» = −log(ππ»−) pOH=14-11.4 pOH= 2.6 2.6 = −log(ππ» − ) 10−2.6 = .0025 π πΎπ = (.0025).0025) 0.153 = 4.08 π₯ 10−5 11. Formic acid is a weak monoprotic acid that is partly responsible for the irritation of insect bites. If the initial concentration of formic acid is 0.1 M and the equilibrium concentration of both the H+ and the conjugate base are 4.2 x 10-3, calculate Ka for formic acid. ο· πΎπ = (4.2 π₯ 10−3 )(4.2 π₯ 10−3 ) 0.1 = 1.76 π₯ 10−4 12. The acetate ion is a very weak base. If the initial concentration of acetate ion in solution is 0.1 M, and the equilibrium concentration of OH- is 7.5 x 10-6 M, calculate Kb for the acetate ion. ο· πΎπ = (7.5 π₯ 10−6 )(7.5 π₯ 10−6 ) 0.1 = 5.63 π₯ 10−10 13. How many moles of LiOH are needed to exactly neutralize 2.0 moles of H2SO4? ο· H2SO4(aq) + 2LiOH(aq) βΆ 2H2O(l) + Li2SO4(aq) 2.0 πππππ π»2 ππ4 × 2πππππ πΏπππ» = 4.0 πππππ πΏπππ» 1 πππππ π»2 ππ4 14. How many moles of H2SO4 are needed to neutralize 5.0 moles of NaOH? ο· H2SO4(aq) + 2NaOH(aq) βΆ 2H2O(l) + Na2SO4(aq) 5.0 πππππ ππππ» × 1 πππππ π»2 ππ4 = 2.5 πππππ π»2 ππ4 2 πππππ ππππ» 15. How many moles of HCL are needed to neutralize 0.10 L of 2.0 M NaOH? ο· HCl(aq) + NaOH(aq) βΆ H2O(l) + NaCl(aq) 2.0 πππππ ππππ» 1 πππ π»πΆπ 0.10πΏ × × = 0.2 πππ π»πΆπ 1πΏ 1 πππ ππππ» 1 16. How many moles of NaOH are needed to neutralize 0.010 L of 0.20 M H2SO4? H2SO4(aq) + 2NaOH(aq) βΆ 2H2O(l) + Na2SO4(aq) 0.20 πππππ π»2 ππ4 2 πππ ππππ» 0.10πΏ × × = 0.04 πππ ππππ» 1πΏ 1 πππ π»2 ππ4 1 17. If it takes 15.0 mL of 0.40 M NaOH to neutralize 5.0 mL of HCl, what is the molar concentration of the HCl solution? ο· HCl(aq) + NaOH(aq) βΆ H2O(l) + NaCl(aq) 0.40 πππππ ππππ» 1 πππ π»πΆπ 0.015πΏ 1 × × × = 1.2 π π»πΆπ 1πΏ 1 πππ ππππ» 1 0.005πΏ 18. If it takes 10.0 mL of 2.0 M H2SO4 to neutralize 30.0 mL of KOH, what is the molar concentration of the KOH? ο· H2SO4(aq) + 2KOH(aq) βΆ 2H2O(l) + K2SO4(aq) 2.0 πππππ π»2 ππ4 2 πππ πΎππ» 0.010πΏ 1 × × × = 1.33 π πΎππ» 1πΏ 1 πππ π»2 ππ4 1 0.030πΏ 19. How many mL of 2.0 M H2SO4 are required to neutralize 30.0 mL of 1.0 M NaOH? ο· H2SO4(aq) + 2NaOH(aq) βΆ 2H2O(l) + Na2SO4(aq) 1.0 ππππ ππππ» 1 πππ π»2 ππ4 0.03πΏ 1πΏ × × × = .0075 πΏ ππ 7.5 ππΏ 1πΏ 2 πππ ππππ» 1 2.0 πππ π»2 ππ4 20. How many mL of 0.10 M Ca(OH)2 are required to neutralize 25.0 mL of 0.50 M HNO3? ο· 2HNO3(aq) +Ca(OH)2(aq) βΆ 2H2O(l) + Ca(NO3)2(aq) 0.5 πππππ π»ππ3 1 πππ πΆπ(ππ»)2 0.025πΏ 1πΏ × × × = .0625 πΏ ππ 62.5 ππΏ 1πΏ 2 πππ π»ππ3 1 0.1 πππ πΆπ(ππ»)2