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Acids & Bases STRONG _ completely ionized _ strong electrolyte _ ionic/very polar bonds bonds Strong Acids: HClO4 H2SO4 HI HBr HCl HNO3 vs WEAK _ partially ionized _ weak electrolyte _ some covalent Strong Bases: LiOH NaOH KOH Ca(OH)2 Sr(OH)2 Ba(OH)2 TITRATION Titration of a strong acid with a strong base ENDPOINT = POINT OF NEUTRALIZATION = EQUIVALENCE POINT At the end point for the titration of a strong acid with a strong base, the moles of acid (H+) equals the moles of base (OH-) to produce the neutral species water (H2O). If the mole ratio in the balanced chemical equation is 1:1 then the following equation can be used. MOLES OF ACID = MOLES OF BASE nacid = nbase Since M=n/V MAVA = MBVB TITRATION MAVA = MBVB 1. Suppose 75.00 mL of hydrochloric acid was required to neutralize 22.50 mLof 0.52 M NaOH. What is the molarity of the acid? HCl + NaOH H2O + NaCl Ma Va = Mb Vb rearranges to Ma = Mb Vb / Va so Ma = (0.52 M) (22.50 mL) / (75.00 mL) = 0.16 M Now you try: 2. If 37.12 mL of 0.843 M HNO3 neutralized 40.50 mL of KOH, what is the molarity of the base? Mb = 0.773 mol/L Molarity and Titration TITRATION Titration of a strong acid with a strong base ENDPOINT = POINT OF NEUTRALIZATION = EQUIVALENCE POINT At the end point for the titration of a strong acid with a strong base, the moles of acid (H+) equals the moles of base (OH-) to produce the neutral species water (H2O). If the mole ratio in the balanced chemical equation is NOT 1:1 then you must rely on the mole relationship and handle the problem like any other stoichiometry problem. MOLES OF ACID = MOLES OF BASE nacid = nbase Molarity and Titration • A student finds that 23.54 mL of a 0.122 M NaOH solution is required to titrate a 30.00-mL sample of hydr acid solution. What is the molarity of the acid? • A student finds that 37.80 mL of a 0.4052 M NaHCO3 solution is required to titrate a 20.00mL sample of sulfuric acid solution. What is the molarity of the acid? • The reaction equation is: H2SO4 + 2 NaHCO3 → Na2SO4 + 2 H2O + 2 CO2 Water Equilibrium Water Equilibrium Kw = [H+] [OH-] = 1.0 x 10-14 Equilibrium constant for water Water or water solutions in which [H+] = [OH-] = 10-7 M are neutral solutions. A solution in which [H+] > [OH-] is acidic A solution in which [H+] < [OH-] is basic pH A measure of the hydronium ion • The scale for measuring the hydronium ion concentration [H3O+] in any solution must be able to cover a large range. A logarithmic scale covers factors of 10. The “p” in pH stands for log. • A solution with a pH of 1 has [H3O+] of 0.1 mol/L or 10-1 • A solution with a pH of 3 has [H3O+] of 0.001 mol/L or 10-3 • A solution with a pH of 7 has [H3O+] of 0.0000001 mol/L or 10-7 pH = - log [H3O+] The pH scale The pH scale ranges from 1 to 10-14 mol/L or from 1 to 14. pH = - log [H3O+] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 acid neutral base Manipulating pH Algebraic manipulation of: pH = - log [H3O+] allows for: [H3O+] = 10-pH If pH is a measure of the hydronium ion concentration then the same equations could be used to describe the hydroxide (base) concentration. [OH-] = 10-pOH pOH = - log [OH-] thus: pH + pOH = 14 ; the entire pH range! PRACTICE PROBLEM #25 1. How many milliliters of 1.25 M LiOH must be added to neutralize 34.7 mL of 0.389 M HNO3? 10.8 mL 2. What mass of Sr(OH)2 will be required to neutralize 19.54 mL of 0.00850 M HBr solution? 0.0101 g 3. How many mL of 0.998 M H2SO4 must be added to neutralize 47.9 mL of 1.233 M KOH? 29.6 mL 4. What is the molar concentration of hydronium ion in a solution of pH 8.25? -9 5.623 x 10 M 5. What is the pH of a solution that has a molar concentration of hydronium ion of 9.15 x 10-5? pH = 4.0 6. What is the pOH of a solution that has a molar concentration of hydronium ion of 8.55 x 10-10? pOH = 4.9 GROUP STUDY PROBLEM #25 ______1. How many milliliters of 0.75 M KOH must be added to neutralize 50.0 mL of 2.50 M HCl? ______2. What mass of Ca(OH)2 will be required to neutralize 100 mL of 0.170 M HCl solution? ______3. How many mL of 0.554 M H2SO4 must be added to neutralize 25.0 mL of 0.9855 M NaOH? ______ 4. What is the molar concentration of hydronium ion in a solution of pH 2.45? ______ 5. What is the pH of a solution that has a molar concentration of hydronium ion of 3.75 x 10-9? ______ 6. What is the pOH of a solution that has a molar concentration of hydronium ion of 4.99 x 10-4?