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2 Acids and Bases Section 18.1 Introduction to Acids and Bases Section 18.2 Strengths of Acids and Bases Section 18.3 Hydrogen Ions and ph Section 18.4 Neutralization Click a hyperlink or folder tab to view the corresponding slides. Exit

3 Section 18.1 Introduction to Acids and Bases Identify the physical and chemical properties of acids and bases. Classify solutions as acidic, basic, or neutral. Compare the Arrhenius, Brønsted-Lowry, and Lewis models of acids and bases. Lewis structure: a model that uses electron-dot structures to show how electrons are arranged in molecules

4 Section 18.1 Introduction to Acids and Bases (cont.) acidic solution basic solution Arrhenius model Brønsted-Lowry model conjugate acid conjugate base conjugate acid-base pair amphoteric Lewis model Different models help describe the behavior of acids and bases.

5 Properties of Acids Acids taste sour. Acids are conductors of electricity. Most acids are corrosive. Acids can neutralize bases. Sulfuric and Nitric acids cause damage in acid rain. Acids turn blue litmus red.

6 Properties of Bases Bases taste bitter and feel slippery. Bases are also conductors of electricity. Strong bases can burn your skin. Bases can neutralize acids. Many detergents and cleaning solutions are basic. Bases turn red litmus blue.

7 Properties of Acids and Bases (cont.) All water solutions contain hydrogen ions (H + ) and hydroxide ions (OH ). An acidic solution contains more hydrogen ions than hydroxide ions. A basic solution contains more hydroxide ions than hydrogen ions.

8 Properties of Acids and Bases (cont.) The usual solvent for acids and bases is water water produces equal numbers of hydrogen and hydroxide ions in a process called self-ionization. H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) The hydronium ion is H 3 O +.

9 The Arrhenius Model Arrhenius acid is a substance that contains hydrogen and ionizes to produce hydrogen ions, H +, in solutions. HCl ionizes to produce H+ ions. HCl(g) H+(aq) + Cl (aq)

10 The Arrhenius Model (cont.) Arrhenius base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion, OH-, in solution. NaOH dissociates to produce OH ions. NaOH(s) Na+(aq) + OH (aq)

11 Practical Applications Neutralization has many practical applications. Reclamation (restoration) of land once used for mining also involves neutralization reactions. Neutralization is also used to deal with environmental problems. Acids and bases are used in the manufacture of fertilizers, synthetic fabrics, pigments, petroleum, iron and steel, explosives, dyes, plastics, pesticides, soaps and detergents, paper, film, and many other chemicals.

12 Practical Applications They are also used for various other purposes, including cleaning surfaces, refining oil and sugar, electroplating metals, and treating food products. Sulfuric acid is the chemical most widely used in industry. Nitric acid, another important industrial acid, is used in the manufacture of fertilizers, plastics, photographic film, and dyes and explosives as dynamite and TNT.

13 Practical Applications Hydrochloric acid is used to clean metals, brick and tile; it is used in the manufacture of sugar and glue. ph plays an important role in the chemistry of the body. Softening of water using soda lime process by municipalities and wastewater treatment.

14 Section 18.1 Assessment A Lewis acid is a(n). A. electron pair donor B. hydrogen ion donor C. electron pair acceptor D. substance that contains an hydroxide group A. A B. B C. C D. D

15 Section 18.1 Assessment A conjugate acid is formed when: A. a base accepts a hydrogen ion B. an acid accepts a hydrogen ion C. an acid donates a hydrogen ion D. a base donates a hydrogen ion A. A B. B C. C D. D

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17 Section 18.2 Strengths of Acids and Bases Relate the strength of an acid or base to its degree of ionization. Compare the strength of a weak acid with the strength of its conjugate base. Explain the relationship between the strengths of acids and bases and the values of their ionization constants. electrolyte: an ionic compound whose aqueous solution conducts an electric current

18 Section 18.2 Strengths of Acids and Bases (cont.) strong acid weak acid acid ionization constant strong base weak base base ionization constant In solution, strong acids and bases ionize completely, but weak acids and bases ionize only partially.

19 Strengths of Acids Acids that ionize completely are strong acids. Strong acids produce more H + ions in solution than weak acids. Because they produce the maximum number of hydrogen ions, strong acids are good conductors of electricity.

20 Strengths of Acids (cont.) Acids that ionize only partially in dilute aqueous solutions are called weak acids.

21 Strengths of Bases A base that dissociates completely into metal ions and hydroxide ions is known as a strong base. Strong bases produce more OH - ions than weak bases. A weak base ionizes only partially in dilute aqueous solution.

22 Section 18.2 Assessment A solution with a small K b is a. A. weak acid B. weak base C. strong acid D. strong base A. A B. B C. C D. D

23 Section 18.2 Assessment Where is the equilibrium point in the ionization equation for a strong acid? A. far right B. far left C. slightly right D. slightly left A. A B. B C. C D. D

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25 Section 18.3 Hydrogen Ions and ph Explain ph and poh. Relate ph and poh to the ion product constant for water. Calculate the ph and poh of aqueous solutions. ph and poh are logarithmic scales that express the concentrations of hydrogen ions and hydroxide ions in aqueous solutions. Le Châtelier s principle: states that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress ion product constant for water ph poh

26 Ion Product Constant for Water Pure water contains equal concentrations of H + and OH ions and is neutral. The ion production of water, K w = [H + ][OH ]. The ion product constant for water is the value of the equilibrium constant expression for the self-ionization of water.

27 Ion Product Constant for Water (cont.) With pure water at 298 K, both [H + ] and [OH ] are equal to M. K w at 298 K = x = [H + ] [OH - ]

28 ph and poh ph is the negative logarithm of the hydrogen ion concentration of a solution. ph = log [H + ]

29 ph and poh (cont.) poh of a solution is the negative logarithm of the hydroxide ion concentration. poh = log [OH ] The sum of ph and poh equals 14.

30 ph and poh (cont.) Litmus paper and a ph meter with electrodes can determine the ph of a solution. There are a variety of indicators available over a range of ph values to determine how acidic or basic a solution is.

31 Section 18.3 Assessment In dilute aqueous solution, as [H + ] increases: A. ph decreases B. poh increases C. [OH ] decreases D. all of the above A. A B. B C. C D. D

32 Section 18.3 Assessment What is the ph of a neutral solution such as pure water? A. 0 B. 7 C. 14 D A B A. A B. B C. C 0% 0% 0% 0% D. D C D

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34 Section 18.4 Neutralization Write chemical equations for neutralization reactions. Explain how neutralization reactions are used in acid-base titrations. Compare the properties of buffered and unbuffered solutions. stoichiometry: the study of quantitative relationships between the amounts of reactants used and products formed by a chemical reaction; is based on the law of conservation of mass

35 Section 18.4 Neutralization (cont.) neutralization reaction salt titration titrant equivalence point acid-base indicator end point salt hydrolysis buffer buffer capacity In a neutralization reaction, an acid reacts with a base to produce a salt and water.

36 Reactions Between Acids and Bases A neutralization reaction is a reaction in which an acid and a base in an aqueous solution react to produce a salt and water. A salt is an ionic compound made up of a cation from a base and an anion from an acid.

37 Reactions Between Acids and Bases Neutralization: Acid + Base salt + H 2 O HCl + NaOH NaCl + H 2 O

38 Reactions Between Acids and Bases (cont.) Titration is a method for determining the concentration of a solution by reacting a known volume of that solution with a solution of known concentration.

39 Reactions Between Acids and Bases (cont.) In a titration procedure, a measured volume of an acid or base of unknown concentration is placed in a beaker, and initial ph recorded. A buret is filled with the titrating solution of known concentration, called a titrant.

40 Reactions Between Acids and Bases (cont.) Measured volumes of the standard solution are added slowly and mixed into the solution in the beaker, and the ph is read and recorded after each addition. The process continues until the reaction reaches the equivalence point, which is the point at which moles of H + ion from the acid equals moles of OH ion from the base. An abrupt change in ph occurs at the equivalence point.

41 Reactions Between Acids and Bases (cont.)

42 Reactions Between Acids and Bases (cont.) Chemical dyes whose color are affected by acidic and basic solutions are called acidbase indicators.

43 Reactions Between Acids and Bases (cont.) An end point is the point at which an indicator used in a titration changes color. An indicator will change color at the equivalence point.

44 Salt Hydrolysis In salt hydrolysis, the anions of the dissociated salt accept hydrogen ions from water or the cations of the dissociated salt donate hydrogen ions to water.

45 Salt Hydrolysis (cont.) Salts that produce basic solutions KF is the salt of a strong base (KOH) and a weak acid (HF). KF(s) K + (aq) + F (aq)

46 Salt Hydrolysis (cont.) Salts that produce acidic solutions NH 4 Cl is the salt of a weak base (NH 3 ) and strong acid (HCl). When dissolved in water, the salt dissociates into ammonium ions and chloride ions. NH 4 Cl(s) NH 4+ (aq) + Cl (aq)

47 Salt Hydrolysis (cont.) Salts that produce neutral solutions NaNO 3 is the salt of a strong acid (HNO 3 ) and a strong base (NaOH). Little or no salt hydrolysis occurs because neither Na + nor NO 3 react with water.

48 Buffered Solutions The ph of blood must be kept in within a narrow range. Buffers are solutions that resist changes in ph when limited amounts of acid or base are added.

49 Buffered Solutions (cont.) Ions and molecules in a buffer solution resist changes in ph by reacting with any hydrogen ions of hydroxide ions added to the buffered solution. HF(aq) H + (aq) + F (aq) When acid is added, the equilibrium shifts to the left.

50 Buffered Solutions (cont.) Additional H + ions react with F ions to form undissociated HF molecules but the ph changes little. The amount of acid or base that a buffer solution can absorb without a significant change in ph is called the buffer capacity.

51 Buffered Solutions (cont.) A buffer is most effective when the concentrations of the conjugate acid-base pair are equal or nearly equal.

52 Section 18.4 Assessment In a neutralization reaction, an acid and base react to form: A. salt and oxygen gas B. salt and ammonia C. salt and water D. precipitate and water A. A B. B C. C D. D

53 Section 18.4 Assessment Solutions that resist changes in ph are called. A. titrants B. salts C. conjugate pairs D. buffers A B A. A B. B C. C 0% 0% 0% 0% D. D C D

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55 Chemistry Online Study Guide Chapter Assessment Standardized Test Practice Image Bank Concepts in Motion

56 Key Concepts Section 18.1 Introduction to Acids and Bases The concentrations of hydrogen ions and hydroxide ions determine whether an aqueous solution is acidic, basic, or neutral. An Arrhenius acid must contain an ionizable hydrogen atom. An Arrhennius base must contain an ionizable hydroxide group. A Brønsted-Lowry acid is a hydrogen ion donor. A Brønsted-Lowry base is a hydrogen ion acceptor. A Lewis acid accepts an electron pair. A Lewis base donates an electron pair.

57 Key Concepts Section 18.2 Strengths of Acids and Bases Strong acids and strong bases are completely ionized in a dilute aqueous solution. Weak acids and weak bases are partially ionized in a dilute aqueous solution. For weak acids and weak bases, the value of the acid or base ionization constant is a measure of the strength of the acid or base.

58 Key Concepts Section 18.3 Hydrogen Ions and ph The ion product constant for water, K w, equals the product of the H + ion concentration and the OH ion concentration. K w = [H + ][OH ] The ph of a solution is the negative log of the hydrogen ion concentration. The poh is the negative log of the hydroxide ion concentration. ph plus poh equals 14. ph = log [H + ] poh = log [OH ] ph + poh = A neutral solution has a ph of 7.0 and a poh of 7.0 because the concentrations of hydrogen ions and hydroxide ions are equal.

59 Key Concepts Section 18.4 Neutralization In a neutralization reaction, an acid and a base react to form a salt and water. The net ionic equation for the neutralization of a strong acid by a strong base is H + (aq) + OH (aq) H 2 O(l). Titration is the process in which an acid-base neutralization reaction is used to determine the concentration of a solution. Buffered solutions contain mixtures of molecules and ions that resist changes in ph.

60 Which type of acid accepts an electron pair? A. Arrhenius B. Brønsted-Lowry C. Lewis D. Dalton A. A B. B C. C D. D

61 What is the conjugate of a weak acid? A. strong acid B. strong base C. weak acid D. weak base A B A. A B. B C. C 0% 0% 0% 0% D. D C D

62 In a solution with a ph of 4.0, which of the following is true? A. [H + ] > [OH ] B. [H + ] < [OH ] C. [H + ] = [OH ] D. none of the above A B A. A B. B C. C 0% 0% 0% 0% D. D C D

63 Salt hydrolysis is what type of reaction? A. single-replacement B. double replacement C. synthesis D. decomposition A B A. A B. B C. C 0% 0% 0% 0% D. D C D

64 The strength of a weak acid is measured by: A. ion product constant B. base ionization constant C. poh D. acid ionization constant A B A. A B. B C. C 0% 0% 0% 0% D. D C D

65 What is the poh of 0.250M HBr, a strong acid? A B C D A B A. A B. B C. C 0% 0% 0% 0% D. D C D

66 Which of the following is a diprotic acid? A. CH 2 COOH B. HCl C. NH 3 + D. H 2 SO 4 A B A. A B. B C. C 0% 0% 0% 0% D. D C D

67 What is the conjugate acid in the following equation? HCl(s) + H 2 O H 3 O + (aq) + Cl (aq) A. Cl B. H 3 O + C. H 2 O D. HCl A B A. A B. B C. C 0% 0% 0% 0% D. D C D

68 An increase in concentration of hydrogen ions when hydroxide ions are added to an aqueous solution is an example of: A. an Arrhenius acid B. a Brønsted-Lowry acid C. the equivalence point D. Le Châtelier s Principle A B A. A B. B C. C 0% 0% 0% 0% D. D C D

69 Which of the following is a polar molecule? A. CH 4 B. PCl 5 C. H 2 O D. H 2 A B A. A B. B C. C 0% 0% 0% 0% D. D C D

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87 Table 18.2 Three Models for Acids and Bases Table 18.3 Ionization Equations Figure A Neutralization Reaction Figure Titration Figure Neutralization Reactions

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