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Foundations of College Chemistry, 14 th Ed. Morris Hein and Susan Arena Lemons and limes are examples of foods that contain acidic solutions. 15 Acids,

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Presentation on theme: "Foundations of College Chemistry, 14 th Ed. Morris Hein and Susan Arena Lemons and limes are examples of foods that contain acidic solutions. 15 Acids,"— Presentation transcript:

1 Foundations of College Chemistry, 14 th Ed. Morris Hein and Susan Arena Lemons and limes are examples of foods that contain acidic solutions. 15 Acids, Bases, and Salts Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

2 15.1 Acids and Bases 15.2 Reactions of Acids and Bases 15.3 Salts 15.4 Electrolytes and Nonelectrolytes 15.5 Introduction to pH 15.6 Neutralization 15.7 Writing Net Ionic Equations 15.8 Acid Rain Chapter Outline © 2014 John Wiley & Sons, Inc. All rights reserved.

3 Arrhenius Acid: An acid solution contains an excess of H + ions. Common Properties of Acids 1. Sour taste 2. Turns litmus paper pink 3. Reacts with: Metals to produce H 2 gas Bases to yield water and a salt Carbonates to give carbon dioxide Arrhenius Acids © 2014 John Wiley & Sons, Inc. All rights reserved.

4 Common Properties of Bases 1. Bitter/caustic taste 2. Turns litmus paper blue 3. Slippery, soapy texture 4. Neutralizes acids Arrhenius Bases: A basic solution contains an excess of OH – ions. Arrhenius Bases © 2014 John Wiley & Sons, Inc. All rights reserved.

5 A Brønsted-Lowry acid is a proton (H + ) donor. A Brønsted-Lowry base is a proton (H + ) acceptor. HCl (g) + H 2 O (l) 2 H 3 O + (aq) + Cl - (aq) HCO 3 - (aq) + H 2 O (l) H 2 CO 3 (aq) + OH - (aq) AcidBaseConjugate Base Conjugate Acid conjugate pair 1 conjugate pair 2 AcidBase Conjugate Acid/Base Pairs: Two species that differ from each other by the presence of one hydrogen ion. Hydronium ion (hydrated H + ) Brønsted-Lowry Acids and Bases © 2014 John Wiley & Sons, Inc. All rights reserved.

6 a. H 2 PO 4 - (aq) b. H 2 O (l) c. HPO 4 2- (aq) d. H 3 O + (aq) Identify the base in the following reaction and the compound’s conjugate acid. H 2 PO 4 - (aq) + H 2 O (l) HPO 4 2- (aq) + H 3 O + (aq) Base a. H 2 PO 4 - (aq) b. H 2 O (l) c. HPO 4 2- (aq) d. H 3 O + (aq) Conjugate Acid © 2014 John Wiley & Sons, Inc. All rights reserved. Brønsted-Lowry Acids and Bases

7 Lewis Acid: electron pair acceptor. Lewis Base: electron pair donor. Lewis Acid-Bases © 2014 John Wiley & Sons, Inc. All rights reserved.

8 The theory that best explains the reaction of interest is used. Summary of the Acid/Base Theories © 2014 John Wiley & Sons, Inc. All rights reserved.

9 1. Reactivity with Metals 2 HCl (aq) + Mg (s) MgCl 2 (s) + H 2 (g) Acids react with any metals above hydrogen in the activity series. In general: acid + metal salt + hydrogen 2. Reactivity with Bases 2 HCl (aq) + Ca(OH) 2 (aq) CaCl 2 (aq) + 2 H 2 O (l) Also called a neutralization reaction. acid + base salt + water In general: Reactions of Acids © 2014 John Wiley & Sons, Inc. All rights reserved.

10 3. Reactivity with Metal Oxides 2 HCl (aq) + Na 2 O (s) 2 NaCl (aq) + H 2 O (l) In general: acid + metal oxide salt + water 4. Reactivity with Metal Carbonates 2 HCl (aq) + Na 2 CO 3 (aq) 2 NaCl (aq) + H 2 O (l) + CO 2 (g) acid + carbonate salt + water + carbon dioxide (base) In general: (base) © 2014 John Wiley & Sons, Inc. All rights reserved. Reactions of Acids

11 In general: Bases can be amphoteric (act as either Brönsted acids or bases) Zn(OH) 2 (aq) + 2 HBr (aq) ZnBr 2 (aq) + 2 H 2 O (l) As a base: NaOH and KOH can also react with metals. 2 NaOH (aq) + 2 Al (s) + 6 H 2 O (l) 2 NaAl(OH) 4 (aq) + 3 H 2 (g) base + metal + water salt + hydrogen Zn(OH) 2 (aq) + 2 NaOH (aq) Na 2 Zn(OH) 4 (aq) As an acid: Base Reactions © 2014 John Wiley & Sons, Inc. All rights reserved.

12 HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) Salts: products from acid-base reactions. Salts are ionic compounds. Sodium chloride (table salt) Salts contain a cation (a metal or ammonium ion) derived from the base and an anion (excluding oxide or hydroxide ions) derived from the acid. Salts are generally crystalline compounds with high melting and boiling points. Salts © 2014 John Wiley & Sons, Inc. All rights reserved.

13 3 Al 2 O 3 (s) + 18 HBr (aq) 6 AlBr 3 (aq) + 9 H 2 O (l) Which salt forms in the reaction of aluminum oxide and hydrobromic acid? a. AlBr b. AlBr 3 c. Al 2 Br d. Al 2 Br 3 Salts Practice © 2014 John Wiley & Sons, Inc. All rights reserved.

14 Electrolytes: compounds that conduct electricity when dissolved in water. Nonelectrolytes: substances that do not conduct electricity when dissolved in water. (Sugar solution)(Salt solution) Comparing Solution Conductivity Electrolytes and Nonelectrolytes © 2014 John Wiley & Sons, Inc. All rights reserved. (Distilled water)

15 Ion movement causes conduction of electricity in water. 3 classes of compounds, acids, bases, and salts are electrolytes because they produce ions in water when they dissolve. © 2014 John Wiley & Sons, Inc. All rights reserved. Electrolytes and Nonelectrolytes

16 Which compound will not dissociate in water? a. HCl b. KBr c. NaOH d. CH 3 OH a. HCl (acid, dissociates) b. KBr (salt, dissociates) c. NaOH (base, dissociates) d. CH 3 OH (organic, does not dissociate) Electrolytes and Nonelectrolytes Practice © 2014 John Wiley & Sons, Inc. All rights reserved.

17 Salts dissociate into their respective cations and anions when dissolved in water. NaCl (s) Na + (aq) + Cl - (aq) Hydrated sodium (purple) and chloride (green) ions The permanent dipoles in the water molecules cause specific alignment around the ions. When NaCl dissolves in water, each ion is surrounded by several water molecules. The negative end of the water dipole is attracted to the positive Na + ion. Dissociation of Electrolytes © 2014 John Wiley & Sons, Inc. All rights reserved.

18 Ionization: process of ion formation in solution. Ionization results from the chemical reaction between a compound and water. Acids ionize in water, producing the hydronium ion (H 3 O + ) and a counter anion. HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) H 3 PO 4 (aq) + H 2 O (l) H 2 PO 4 - (aq) + H 3 O + (aq) Bases ionize in water, producing the hydroxide ion (OH - ) and a counter cation. NH 3 (aq) + H 2 O (l) OH - (aq) + NH 4 + (aq) Electrolyte Ionization © 2014 John Wiley & Sons, Inc. All rights reserved.

19 HCl (left) is 100% ionized. CH 3 COOH exists primarily in the unionized form. Strong electrolytes: undergo complete ionization in water. Example: HCl (strong acid) Weak electrolytes: undergo incomplete ionization in water. Example: CH 3 COOH (weak acid) Strong and Weak Electrolytes © 2014 John Wiley & Sons, Inc. All rights reserved.

20 HF (aq) + H 2 O (l) F - (aq) + H 3 O + (aq) Double arrows indicate incomplete ionization (typically weak electrolytes). © 2014 John Wiley & Sons, Inc. All rights reserved. Strong and Weak Electrolytes

21 CaCl 2 (s) Ca 2+ (aq) + 2 Cl - (aq) NaCl (s) Na + (aq) + Cl - (aq) Salts can dissociate into more than 2 ions, depending upon the compound. A 1 M solution of NaCl produces a total of 2 M of ions. A 1 M solution of CaCl 2 produces a total of 3 M of ions. 1M 2M Salts © 2014 John Wiley & Sons, Inc. All rights reserved.

22 MgBr 2 (s) Mg 2+ (aq) + 2 Br - (aq) What is the concentration of bromide ion in a 1.5 M solution of magnesium bromide? a. 0.75M b. 1.5M c. 3.0M d. 4.5M 1.5 M 3.0M For every one mole of MgBr 2, 2 moles of Br - ionize. Salts Practice © 2014 John Wiley & Sons, Inc. All rights reserved.

23 Colligative properties: depend only on the number of moles of dissolved particles present. This must be taken into consideration when calculating freezing point depression or boiling point elevation due to the presence of solute particles. Example: What is the boiling point elevation of a 1.5 m aqueous solution of CaCl 2 ? (K b for water is ºC/m). Δ T b = 1.5 m CaCl 2 = 2.3 ºC × 3 mol ions 1 mol CaCl ºC 1 m Because CaCl 2 is a strong electrolyte, 3 mol of ions (1 mol Ca 2+ and 2 mol Cl - ions) will be present in the solution. × Colligative Properties of Electrolyte Solutions © 2014 John Wiley & Sons, Inc. All rights reserved.

24 What is the boiling point of a 2.0 m aqueous solution of NaCl? (K b for water = ºC/m) a ºC b ºC c ºC d ºC Δ T b = 2.0 m NaCl = 2.05 ºC × 2 mol ions 1 mol NaCl ºC 1 m Because NaCl is a strong electrolyte, 2 mol of ions (1 mol Na + and 1 mol Cl - ions) will be present in the solution. T b = ºC ºC = ºC × Colligative Properties of Electrolytes Practice © 2014 John Wiley & Sons, Inc. All rights reserved.

25 Pure water auto(self) ionizes according to the reaction: H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH – (aq) Based on the reaction stoichiometry: Concentration H 3 O + = Concentration OH – = 1 x 10 –7 M [H 3 O + ] x [OH – ] = (1 x 10 –7 ) 2 = 1 x 10 –14 When acid or base is present in water, [H 3 O + ] and [OH - ] change. In acidic solutions, [H 3 O + ] > [OH – ]. In basic solutions, [H 3 O + ] < [OH – ]. Autoionization of Water © 2014 John Wiley & Sons, Inc. All rights reserved.

26 In pure water, [H 3 O + ] = 1 x M, so pH = - log(1 x ) = 7 Increasing acidity Increasing basicity Neutral High H 3 O + Low OH - Low H 3 O + High OH - The pH scale pH = - log[H 3 O + ] Introduction to pH © 2014 John Wiley & Sons, Inc. All rights reserved.

27 pH © 2014 John Wiley & Sons, Inc. All rights reserved.

28 a. 2 b. 20 c. 200 d. 100 By what factor is a solution of pH = 3 more acidic than a solution with a pH = 5? pH = 5 means [H 3 O + ] = 1 x M pH = 3 means [H 3 O + ] = 1 x M Factor = 1 x M 1 x M = 100 pH Practice © 2014 John Wiley & Sons, Inc. All rights reserved.

29 pH = - log[H 3 O + ] [H 3 O + ] = 1 x M [H 3 O + ] = 2 x M If exactly 1 Exponent = pH pH = 5 If a number between 1 and 10 The pH is between the exponent and next lowest whole number pH = 4.7 Generalizations [H 3 O + ] = 10 -pH pH Calculations © 2014 John Wiley & Sons, Inc. All rights reserved.

30 Calculate the pH of a M [H 3 O + ] solution. pH = - log(0.015) = 1.8 Note: the digits to the left of the decimal place in the pH reflect the power of ten from the [H 3 O + ]. The number of decimal places for the mantissa must equal the number of significant figures in the original number. © 2014 John Wiley & Sons, Inc. All rights reserved. pH Calculations

31 What is the pH of a M HCl solution? pH = - log(0.020) = 1.7 a b c d. 1.7 pH Calculations Practice © 2014 John Wiley & Sons, Inc. All rights reserved.

32 What is the pH of a NaOH solution with a [OH - ] = 2.5 x M? pH = - log(4.0 x ) = 3.4 [H 3 O + ] x [OH - ] = 1 x a. 3.4 b c d [H 3 O + ] = 1 x /[OH - ] = 1 x /2.5 x = 4.0 x M © 2014 John Wiley & Sons, Inc. All rights reserved. pH Calculations Practice

33 General Reaction Overall Ionic Equation: HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) acid + base salt + water Example H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq) Na + (aq) + Cl - (aq) + H 2 O (l) All species are included; soluble compounds shown as ions. Net Ionic Equation: H + (aq) + OH - (aq) H 2 O (l) Spectator ions (green) are removed from both sides. Neutralization © 2014 John Wiley & Sons, Inc. All rights reserved.

34 Titration: experiment where the volume of one reagent (titrant) required to react with a measured amount of another reagent is measured. Titrations allow the amount of an acid or base present in a sample to be determined. Indicators are used to signal the endpoint of a titration, the point when enough titrant is added to react with the acid/base present. Burets deliver measured amounts of the titrant into a solution of the unknown reagent. Endpoint Titration © 2014 John Wiley & Sons, Inc. All rights reserved.

35 If mL of M HCl is used to titrate mL of NaOH, what is the molarity of the base? Reaction Knowns mL of M HCl mL NaOH HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) Solving for Molarity of base mol HCl 1000 mL soln mL Calculate = mol NaOH 1 mol NaOH 1 mol HCl ×× Molarity NaOH = mol NaOH L soln = M NaOH Titration Calculations © 2014 John Wiley & Sons, Inc. All rights reserved.

36 What is the molarity of a NaOH solution if mL of base is required to titrate g of oxalic acid (H 2 C 2 O 4 )? Reaction Knowns g H 2 C 2 O mL NaOH H 2 C 2 O 4 (aq) + 2 NaOH (aq) NaC 2 O 4 (aq) + 2 H 2 O (l) Solving for Molarity of base 1 mol H 2 C 2 O g H 2 C 2 O g H 2 C 2 O 4 Calculate = mol NaOH 2 mol NaOH 1 mol H 2 C 2 O 4 × Molarity NaOH = mol NaOH L soln = M NaOH × Always check reaction stoichiometry! © 2014 John Wiley & Sons, Inc. All rights reserved. Titration Calculations

37 What is the concentration of a nitric acid solution if 10.0 mL of the solution is neutralized by 3.6 mL of 0.20 M NaOH? a M b M c M d. 5.6 M Reaction HNO 3 (aq)+NaOH(aq) NaNO 3 (aq)+2 H 2 O(l) Knowns 3.60 mL, 0.20 M NaOH mL HNO 3 Solving for Molarity of acid 0.20 mol NaOH 1000 mL NaOH 3.60 mL NaOH Calculate = mol HNO 3 1 mol HNO 3 1 mol NaOH × Molarity HNO 3 = mol HNO L soln = M HNO 3 × © 2014 John Wiley & Sons, Inc. All rights reserved. Titration Calculations Practice

38 Rules for Writing Net Ionic Equations 1. Strong electrolytes are written as the corresponding ions. Example: NaOH (aq) is written as Na + (aq) + OH - (aq) 2. Weak electrolytes and nonelectrolytes are written as molecules. Example: CH 3 OH(aq), CH 3 COOH(aq), etc. 3. Solids and gases are written as their molecular forms. 4. The net ionic equation does not include spectator ions. 5. The net ionic equation must balance atoms and charge. Net Ionic Equations © 2014 John Wiley & Sons, Inc. All rights reserved.

39 Write the net ionic equation (NIE) for the following reaction: Total Ionic Equation BaCl 2 (aq) + Na 2 SO 4 (aq) BaSO 4 (aq) + 2 NaCl (aq) Net Ionic Equation Ba 2+ (aq) + 2 Cl - (aq) + 2 Na + (aq) + SO 4 2- (aq) BaSO 4 (s) + 2 Na + (aq) + 2 Cl - (aq) Spectator Ions Ba 2+ (aq) + SO 4 2- (aq) BaSO 4 (s) Net Ionic Equations Practice © 2014 John Wiley & Sons, Inc. All rights reserved.

40 Write the net ionic equation (NIE) for the following reaction: Total Ionic Equation Na 2 CO 3 (aq) + 2 HCl (aq) CO 2 (g) + 2 NaCl (aq) + H 2 O (l) Net Ionic Equation 2 Na + (aq) + CO 3 2- (aq) + 2 H + (aq) + 2 Cl - (aq) 2 Na + (aq) + 2 Cl - (aq) + CO 2 (g) + H 2 O (l) Spectator Ions 2 H + (aq) + CO 3 2- (aq) CO 2 (g) + H 2 O (l) © 2014 John Wiley & Sons, Inc. All rights reserved. Net Ionic Equations Practice

41 What is the net ionic equation when hydrobromic acid reacts with potassium hydroxide? a. b. c. d. H + (aq) + Br - (aq) HBr (l) K + (aq) + OH - (aq) KOH (s) K + (aq) + H - (aq) KH (s) H + (aq) + OH - (aq) H 2 O (l) Total Ionic Equation H + (aq)+Br - (aq)+K + (aq)+OH - (aq) K + (aq)+Br - (aq)+H 2 O(l) HBr (aq) + KOH (aq) KBr (aq) + H 2 O (l) Equation © 2014 John Wiley & Sons, Inc. All rights reserved. Net Ionic Equations Practice

42 Acid rain: atmospheric precipitation more acidic than typical. General Process for Acid Rain Formation: 1. Emission of nitrogen or sulfur oxides. 2. Transportation of these chemicals throughout the atmosphere. 3. Chemical reaction of the oxides with water. This forms sulfuric and nitric acids. 4. Precipitation carries the acids to the ground. Acid Rain © 2014 John Wiley & Sons, Inc. All rights reserved.

43 Compare the definitions of acids and bases, including Arrhenius, Brønsted-Lowry, and Lewis acids/bases Acids and Bases Describe the general reactions of acids and bases Reactions of Acids and Bases Explain how a salt is formed and predict the formula of a salt given an acid and base precursor Salts Learning Objectives © 2014 John Wiley & Sons, Inc. All rights reserved.

44 Describe properties, ionization, dissociation, and strength of electrolytes and compare them to nonelectrolytes Electrolytes and Nonelectrolytes Calculate the pH of a solution from the hydrogen ion concentration Introduction to pH Describe a neutralization reaction and do calculations involving titrations Neutralization © 2014 John Wiley & Sons, Inc. All rights reserved. Learning Objectives

45 Write net ionic equations using the stated rules Writing Net Ionic Equations Describe how acid rain forms and the effects on society Acid Rain © 2014 John Wiley & Sons, Inc. All rights reserved. Learning Objectives


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