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Chapter 14

Chapter 14. Acids and Bases. Homework. Assigned Questions and Problems (odd only) Section 14.1 (14.1 to 14.5) Section 14.2 (14.7 to 14.15) Section 14.3 (14.17 to 14.25) Section 14.4 Section 14.5 (14.31 to 14.39) Section 14.6 (14.41 to 14.49) Section 14.7 (14.51 to 14.55)

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Chapter 14

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  1. Chapter 14 Acids and Bases

  2. Homework • Assigned Questions and Problems (odd only) • Section 14.1 (14.1 to 14.5) • Section 14.2 (14.7 to 14.15) • Section 14.3 (14.17 to 14.25) • Section 14.4 • Section 14.5 (14.31 to 14.39) • Section 14.6 (14.41 to 14.49) • Section 14.7 (14.51 to 14.55) • Section 14.8 (14.57 to 14.63) • Additional Questions and Problems and Challenge Questions (except 14.99, 14.105)

  3. Acids • Among the most common and important compounds • Aqueous solutions are important in biological systems and in chemical industrial processes • Characteristics • Cause sour taste of lemons and vinegar • Digest food in stomach • Dissolves some metals generating hydrogen gas • Chemical produced in the largest quantity in the USA • Sulfuric acid H2SO4

  4. Acids • Acids • When dissolved in water will generate H+ and an anion • The H+ that is generated will give a sour taste • Vinegar (acetic acid) • Lemon (citric acid) • Most acids are oxo acids (will also gen. H+)

  5. Naming Binary Acids • Use the prefix hydro- before the root name of the element • Add the suffix-ic and the word acid to the root name for the element • Example: HCl • hydrochloricacid • Example: HI • hydroiodicacid

  6. Naming Oxo Acids • Produce H+ and a polyatomic ion when dissolved in water • Composed of hydrogen, oxygen, and another nonmetal • Use the root name of the polyatomic ion • If it ends in -ate use the suffix -ic acid • If it ends in -ite use the suffix -ous acid • Example: H2SO4 (from SO42- , sulfate ion) • sulfuric acid • Example: H2SO3 (from SO32- , sulfite ion) • sulfurous acid

  7. Bases • Bases • When dissolved in water will generate OH- and a metal ion. • Sometimes called alkalis • The OH- that is generated will give a bitter taste • Slippery feel (like soap) • Most bases that are generated are composed from group 1A and 2A metals

  8. Naming Bases • Most bases are usually ionic compounds • The hydroxide ion has a charge of (-1) and is combined with a positively charged ion (group IA or IIA metal ion) • Hydroxides (bases) are named by their cation first, then the word “hydroxide” is added to the metal cation • Most common bases: • NaOH (sodium hydroxide) • KOH (potassium hydroxide) • Ca(OH)2 (calcium hydroxide) • NH4OH (ammoniumhydroxide)

  9. Arrhenius • First person to recognize the essential nature of acids and bases • Acids: • Produce hydrogen ions (H+) in water • Bases • Produce hydroxide ions (OH-) in water

  10. Brønsted-Lowry Acids and Bases • Limitations to Arrhenius model • Only for aqueous solutions • Free H+ does not exist in water • New model by Brønsted and Lowry • Acid • Any substance that can donate a proton (H+) to another substance: Proton donor • Base • Any substance that can accept a proton from another substance: Proton acceptor

  11. Water as a Base • H+ does not exist in water due to the strong attraction to the polar water molecule • H3O+ is called a hydronium ion • Real way that protons exist in water

  12. Brønsted-Lowry Model • The reaction involves a proton transfer • Acid can lose its proton to form a conjugatebase (something that could accept a proton back again) • Base accepts a proton to form a conjugate acid (something that could donate a proton) Conjugate Acid Acid Base Conjugate Base

  13. Brønsted-Lowry Model • The HCl is the Brønsted-Lowry acid because it is donating proton (H+) to water molecule • The water molecule is the Brønsted-Lowry base since it accepts a proton Base Conjugate Base Conjugate Acid Acid

  14. Conjugate Acid/Base Pairs • Related to each other by donating/accepting a single proton (H+) • The acid of the pair has the proton • The base of the pair does not • Every acid has a conjugatebase • Every base has a conjugate acid • “Conjugate” is given to the part of the pair that is produced in the reaction

  15. Conjugate Acid/Base Pairs • Each acid is related to a base on the opposite side • If on the reactants side (left side) substances are called “acid” or “base” • If on the products side (right side) substances are called “conjugate acid” or “conjugate base” Conjugate Acid Conjugate Base Acid Base

  16. Conjugate Acid/Base Pairs • Which of the following represent conjugate acid-base pairs? • H2O, H3O+ • OH-, HNO3 • H2SO4, SO42- • HC2H3O2, C2H3O2-

  17. Conjugate Acid/Base Pairs • H2O, H3O+ • OH-, HNO3 • H2SO4, SO42- • HC2H3O2, C2H3O2-

  18. Strength of Acids • When an acid dissolves in water, it gives its proton to water to form the conjugate base of the acid and a hydronium ion (H3O+) • The strength of the acid is determined by the amount of H3O+ that is produced

  19. Strength of Acids • Strong acids completely dissociate and form H3O+ • If a weak acid, there is nothing stopping the conjugate base and the hydronium ion from reacting to re-form the acid and water Forward Reverse

  20. Strength of Acids • There is a competition for the proton between the conjugate base and water • Water wins: Acid dissociates completely. It is a strong acid • Conjugate base wins: Acid doesn’t dissociate a lot. It is a weak acid

  21. Strong Acids • Dissociate 100% (almost) • Have very weak conjugate bases (weak reverse reaction) • Conjugate base does not react readily with H3O+ • Forward reaction predominates

  22. Weak Acids • Don’t dissociate very much • Have stronger conjugate bases • Conjugate base does react readily with H3O+ • Reverse reaction predominates

  23. Types of Acids • Multiprotic Acids • Can donate more than one proton • H2SO4 • H3PO4 Strong Acid Weak Acid

  24. Types of Acids • Oxo Acids • Acid hydrogen is attached to an oxygen • Acids of Polyatomic Ions

  25. Types of Acids • Organic Acids • Acids with a carbon backbone (carboxyl group) • Acetic Acid (CH3COOH or HC2H3O2)

  26. Ionization of Water • Water can act as an acid or a base • Amphoteric substance Base Acid Conj Acid Conj Base

  27. Ionization of Water • In sample of pure water a small percentage has dissociated to produce ions • It involves a proton transfer • Results in an equal amount of H+ and OH- Base Acid Conj Acid Conj Base

  28. Ionization of Water • Autoionization • Ionizing of water to form hydronium and hydroxide ions at 25 ºC • Doesn’t occur to a large extent • Square brackets around a compound mean “concentration of”

  29. Ion-Product Constant for Water • At any temperature, the product of the concentration of H+ and OH- is always a constant • Valid in pure water or water with solutes • Kw (Ion-Product Constant of Water) • Conc. of ion expressed in moles/liter • Is 1x10-14

  30. Ion-Product Constant for Water • If the [H+] is increased by the addition of acidic solute, the [OH-] must decrease until the expression is 1.0 × 10-14 again • Or, if the OH- ions are added to the water, the H+ must likewise decrease

  31. Ion-Product Constant for Water • An acid is a substance that will increase the H+ ions in solution • All acidic solutions have a higher [H+] than [OH-] • An base is a substance that will increase the OH- ions in solution • All basic solutions have a higher [OH-] than [H+]

  32. Ion-Product Constant for Water • Neutral Solution • Acidic Solution • Basic Solution • In all cases:

  33. Example • Calculate [H+] in a solution in which [OH-] = 2.0x10-2 M. Is this solution acidic, basic or neutral?

  34. The pH Scale • H+ concentrations range from very high values to extremely small valves • Difficult and inconvenient to work with numbers over such a large range • i.e. [H+]of10 M is 1000 trillion times greater than 10-14 • The pH scale of a solution was proposed as an easier and more practical way to handle such large numbers

  35. p Scale • Used to express very small numbers • Based on log 10 • If N is a number then pN is: • Take the log of the number and then multiply by (-1) to change the sign

  36. The pH Scale • The pH scale is defined as the negative log of the molar hydrogen ion concentration • Logarithms are exponents • The negative powers of 10 in the concentrations are converted to positive numbers

  37. Calculating the pH of Solutions • The negative log of the H+ concentration • To determine the number of significant Figures for logs: The number of decimal places for the log is equal to the number of sig. figs. in the concentration (original number)

  38. pH Examples • Calculate the pH for each of the following solutions • A solution in which [H+]=1.0x10-3 M • A solution in which [OH-]=5.0x10-5 M

  39. pH Examples

  40. pH Scale • pH is a log scale • A change in one unit on the pH scale means a tenfold increase or decrease in [H+] • Every time exponent changes by one, the pH changes by one • lowering the pH increases the [H+] • Small pH = acidic solution • Large pH = basic solution

  41. Measuring pH • Use a pH meter • Electronic device that measures the pH of the solution • Use pH paper • Paper has a chemical in it that changes to different colors depending on the pH of the solution

  42. pOH Scale • Same as pH scale, but associated with the [OH-] • Low [OH-] means high pOH • High [OH-] means low pOH

  43. pH and pOH • In an aqueous solution, the sum of the pH and pOH is always 14 • The value 14 corresponds to the negative log of Kw

  44. pH and pOH [H+] > [OH-] [H+] = [OH-] [H+] < [OH-]

  45. Example 1 • A sample of rain in an area with severe air pollution has a pH of 3.5. What is the pOH of this rain water?

  46. Example 2 • The pH of rainwater in a polluted area was found to be 3.50. What is the [H+] for this rainwater?

  47. Example 3 • The pOH of a liquid drain cleaner was found to be 10.50. What is the [OH-] for this cleaner?

  48. Calculating pH for Strong Acids • Strong acids dissociate 100% • Solution contains only H+ and the anion of the acid • Find the concentration of H+ • Find the pH

  49. pH of Strong Acids • Calculate the pH of a solution of 5.0x10-3 M HCl complete dissociation

  50. Reactions of Acids and Bases • Neutralization: The reaction between an acid and a base to form a salt and water • H+ from the acid combines with the OH- from the base to form water • The properties of the both reactants are neutralized • The salt contains the positive ion from the base and the negative ion from the acid

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