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Chemistry The Science in Context Chapter 16 Equilibrium in the Aqueous Phase

HCl(aq) reacting with NH 3 (aq). Chemistry The Science in Context Chapter 16 Equilibrium in the Aqueous Phase. The color of hydrangea flowers depends on the acid content of the soil. Acid rain forms when volatile, nonmetal oxides react with water vapor. SO 3 + H 2 O ↔ H 2 SO 4.

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Chemistry The Science in Context Chapter 16 Equilibrium in the Aqueous Phase

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  1. HCl(aq) reacting with NH3(aq) ChemistryThe Science in ContextChapter 16Equilibrium in the Aqueous Phase

  2. The color of hydrangea flowers depends on the acid content of the soil

  3. Acid rain forms when volatile, nonmetal oxides react with water vapor. SO3 + H2O ↔ H2SO4

  4. »PC version This tutorial explores the effects of fossil fuel burning on the pH of rainwater, as well as the resulting environmental and industrial consequences. Includes practice exercises. Acid Rain Tutorial

  5. Strong Acid HNO3 Weak Acid HNO2

  6. Acids…A molecular view. Acids (proton donors) react with bases (proton acceptors) forming a conjugate acid (H3O+) and conjugate base (Cl-). Note that the conjugate base of a strong acid like HCl is a weak base.

  7. Water molecules in acid solutions cluster around the Hydronium ion. These “species” have the formula: H(H2O)n+

  8. Autoionization of Water Water molecules have the ability to ionize each other. Keq = [H3O+][OH-] = 1.0E-14 (25°C) This important equilibrium constant is usually denoted Kw

  9. Ammonia is a weak base in water, Kb = 1.8E-5 conj. acid conj. base

  10. Trends in acid strength relative to the strength of their conjugate bases. In water the strongest base is OH-; stronger bases will ionize water to produce hydroxide ions.

  11. Problem Benzoic acid is used as a preservative in foods. Calculate the concentration of H+ ions at equilibrium in a 0.100 M solution of Benzoic acid. Ka = 6.5E-5 In Solution, to what degree is benzoic acid ionized?

  12. The pH of a solution is defined as the negative logarithm of the hydronium ion concentration: pH = -log([H+]) Note that Ka and Kb values are frequently reported as pKa and pKb. This avoids writing the values as exponentials.

  13. 16.30. Calculate the pH of a 0.00500 M solution of HNO3. Answer: 2.301 (4 S.F.)

  14. Auto-ionization and pH H2O ↔ H+ + OH- Kw = 1.0E-14; pKw = 14.00 at 298K In pure water, [H+] = [OH-] So [H+]2 = 1.0E-14 Thus [H+] = 1.0E-7 Or pH = 7.0

  15. 16.31. Calculate the pH and pOH of a 0.0450 M solution of NaOH. Answer: pOH=1.347; pH=14.000 – 1.347 = 12.65

  16. Problem: A solution of HF has a pH=2.30. Calculate the equilibrium concentration of all species present in this solution, and the original concentration of the HF (i.e. before dissociation). pKa(HF) = 3.14

  17. For the reaction: HA ↔ H+ + A- The concentration of H+ is a function of the strength of the H-A bond

  18. Acid Strength and Molecular Structure Sulfuric acid is a stronger acid than sulfurous acid due to the decrease in electron density on the O-H bond.

  19. The oxyacids of chlorine increase in strength (Ka) with increasing numbers of oxygen atoms bound to the central chlorine atom.

  20. Blue color indicates increasing positive charge on the proton HClO HBrO HIO rH-O= 0.961Å rH-O= 0.957Å rH-O= 0.955Å Increased H-O bond distance is due to decreased electron density

  21. Problem The pH of a 0.10M solution of chloroacetic acid is found to be 1.95. Calculate Ka for this acid and compare it to Ka for acetic acid.

  22. Polyprotic Acid Ionization The H+ concentration due to the second dissociation is generally insignificant, i.e. compared with the first dissociation.

  23. 16.59. What is the pH of a 0.300 M solution of H2SO4 (Ka2 = 1.2  10–2)?

  24. Problem Methylamine is a weak base (Kb=4.4E-4). Calculate the OH- concentration in a 0.200M aqueous solution of CH3NH2. What is the pH of this solution?

  25. »PC version This tutorial explores the differences among Brønsted-Lowry acids, Brønsted-Lowry bases, Lewis acids and Lewis Bases. Includes practice exercises. Acid and Base Ionization Tutorial

  26. »PC version Learn to determine relative acid strength based on the molecular and electronic structure of the acid. Includes practice exercises. Acid Strength and Molecular Structure Tutorial

  27. »PC version This tutorial introduces the pH scale and uses interactive graphs to explain the relationship between pH, pOH [H3O+], and [OH-]. Includes practice exercises. pH Scale Tutorial

  28. »PC version This tutorial illustrates the process by which water molecules act as both a proton acceptor (base) and a proton donor (acid), and explores the equilibrium constant (Kw) for the self-ionization of water. Includes practice exercises. The Self-Ionization of Water Tutorial

  29. Salts of weak acids and bases. Many naturally occurring compounds used as drugs act as weak bases (due to amine groups). For this reason they are often referred to as alkaloids…they produce alkaline solution.

  30. Problem 63. Which of the following salts produce an acidic solution in water? Ammonium acetate NH4Cl Sodium formate

  31. Problem 63. Which of the following salts produce an basic solution in water? NaF KCl Sodium bicarbonate

  32. Problem 66 Codeine is a widely-prescribed pain killer because it is much less addictive than morphine (which is much less addictive than heroin). Codeine contains a basic nitrogen atom that can be protonated to form the conjugate acid . Calculate the pH of a 3.97E-4 M solution of codeine if the pKa of the conjugate acid is 8.21.

  33. Problem. For a 6.75E-3 M solution of sodium benzoate, determine the following: Identify the equilibrium reaction that determines the pH. Calculate the pH. pKa(benzoic acid) = 4.20

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