Chemistry—Ch. 19: Acids, Bases, and Salts 19.1—Acid-Base Theories main ideas: properties of acids/bases, Arrhenius, Bronsted- Lowry 19.2—Hydrogen Ions and Acidity main ideas: hydrogen ions from water, pH, indicators 19.3—Strengths of Acids and Bases main ideas: what makes acid “strong” or “weak” 19.4—Neutralization Reactions main ideas: acid/base yields salt/water, titration, endpoint 19.5—Salts in Solution main idea: what is a buffer

19.1 19.1 Acid-Base Theories Bracken Cave, near San Antonio, Texas, is home to twenty to forty million bats. Visitors to the cave must protect themselves from the dangerous levels of ammonia in the cave. Ammonia is a byproduct of the bats’ urine. You will learn why ammonia is considered a base.

Properties of Acids and Bases 19.1 Properties of Acids and Bases Acids taste sour pH less than 7 Change blue litmus paper red Red to orange color with universal indicator Contain excess H+ ions Corrosive to metal and skin React with bases to form water and a salt Citrus fruits contain citric acid. Tea contains tannic acid.

Properties of Acids and Bases Bases taste bitter feel slippery pH greater than 7 change red litmus paper blue Blue with universal indicator; pink with phenolphthalein Caustic React with acids to form water and a salt Antacids use bases to neutralize excess stomach acid. The base calcium hydroxide is a component of mortar.

Properties of Acids and Bases 19.1 Properties of Acids and Bases Both acids and bases can be strong or weak electrolytes in aqueous solution. Conductivity tests the extent of ionization in water; weak acids and bases do not ionize completely whereas strong acids and bases do Examples: Strong acid is HCl; weak acid is CH3COOH (also known as HCH3COO or HC2H3O2) Strong base is NaOH; weak base is NH3 (also known as NH4OH)

19.1 Acids and Bases There are several definitions of an acid and a base. Arrhenius is a simple, but limited definition. The Lewis definition is much more comprehensive. Some substances would be considered an acid using one definition, but not using another.

Arrhenius Acids and Bases 19.1 Arrhenius Acids and Bases Arrhenius said that acids are hydrogen-containing compounds that ionize to yield hydrogen ions (H+) in aqueous solution. He also said that bases are compounds that ionize to yield hydroxide ions (OH–) in aqueous solution.

Arrhenius Acids and Bases 19.1 Arrhenius Acids and Bases Arrhenius Acids Acids that contain one ionizable hydrogen, such as nitric acid (HNO3), are called monoprotic acids. Acids that contain two ionizable hydrogens, such as sulfuric acid (H2SO4), are called diprotic acids. Acids that contain three ionizable hydrogens, such as phosphoric acid (H3PO4) are called triprotic acids.

Arrhenius Acids and Bases 19.1 Arrhenius Acids and Bases Arrhenius Bases Milk of magnesia is a base used as an antacid.

Brønsted-Lowry Acids and Bases 19.1 Brønsted-Lowry Acids and Bases The Brønsted-Lowry theory defines an acid as a hydrogen-ion donor, and a base as a hydrogen-ion acceptor.

Brønsted-Lowry Acids and Bases 19.1 Brønsted-Lowry Acids and Bases Conjugate Acids and Bases A conjugate acid is the particle formed when a base gains a hydrogen ion. A conjugate base is the particle that remains when an acid has donated a hydrogen ion. The acid and base are always on the left with the corresponding conjugate acid-base pair on the right.

Brønsted-Lowry Acids and Bases 19.1 Brønsted-Lowry Acids and Bases A conjugate acid-base pair consists of two substances related by the loss or gain of a single hydrogen ion. A substance that can act as both an acid and a base is said to be amphoteric.

Brønsted-Lowry Acids and Bases 19.1 Brønsted-Lowry Acids and Bases A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion (H3O+). When sulfuric acid dissolves in water, it forms hydronium ions and hydrogen sulfate ions. Identify which ion is the conjugate acid and which he the conjugate base?

19.1 Lewis Acids and Bases Lewis proposed that an acid accepts a pair of electrons during a reaction, while a base donates a pair of electrons. A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. A Lewis base is a substance that can donate a pair of electrons to form a covalent bond.

19.1 Section Quiz. 1. Which of the following is NOT a characteristic of acids? a) taste sour b) are electrolytes c) feel slippery d) affect the color of indicators

19.1 Section Quiz. 2.Which compound is most likely to act as an Arrhenius acid? a) H2O b) NH3. c) NaOH. d) H2SO4.

19.1 Section Quiz. 3. A Lewis acid is any substance that can accept a) a hydronium ion. b) a proton. c) hydrogen. d) a pair of electrons.

19.2 Hydrogen Ions and Acidity To test a diagnosis of diabetic coma, a doctor orders several tests, including the acidity of the patient’s blood. Results from this test will be expressed in units of pH. You will learn how the pH scale is used to indicate the acidity of a solution and why the pH scale is used.

Hydrogen Ions from Water 19.2 Hydrogen Ions from Water The reaction in which water molecules produce ions is called the self-ionization of water. In the self-ionization of water, a proton (hydrogen ion) transfers from one water molecule to another water molecule.

Ion Product Constant for Water The product of the concentrations of the hydrogen ions and hydroxide ions in water is called the ion-product constant for water (Kw). For aqueous solutions, the product of the hydrogen-ion concentration and the hydroxide-ion concentration equals 1.0  10-14. Any aqueous solution in which [H+] and [OH-] are equal is described as a neutral solution. The [ ] represents concentration of the ions. The appropriate unit is M (molarity).

Ion Product Constant for Water 19.2 Ion Product Constant for Water An acidic solution is one in which [H+] is greater than [OH-]. A basic solution is one in which [H+] is less than [OH]. Basic solutions are also known as alkaline solutions. Unrefined hydrochloric acid, commonly called muriatic acid, is used to clean stone buildings and swimming pools. Sodium hydroxide, or lye, is commonly used as a drain cleaner.

The pH Concept pH and Significant Figures 19.2 [OH-] 10-14 100 The pH scale shows the relationship between pH and the hydrogen-ion concentration. Interpreting Diagrams What happens to [H+] as pH increases? A solution in which [H+] is greater than 1  10–7 M has a pH less than 7.0 and is acidic. The pH of pure water or a neutral aqueous solution is 7.0. A solution with a pH greater than 7 is basic and has a [H+] of less than 1  10–7 M.

The pH Concept

The pH Concept

The pH Concept 19.2 Kw= [H+][OH-]= 1.0 x 10-14 Use these equations for pH problems. Not written exactly in this manner in the textbook.

Measuring pH 19.2 An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution. Universal Indicator Phenolphthalein changes from colorless to pink at pH 7–9.

19.2 Measuring pH A pH meter provides a quick and accurate way to measure the pH of a solution. a) Water is neutral, having a pH of 7. b) The pH of vinegar, a dilute aqueous solution of ethanoic (acetic) acid, is about 3. c) The pH of milk of magnesia, an aqueous suspension of magnesium hydroxide, is 10.5. Applying Concepts What are some advantages of using a pH meter rather than an indicator? pH Meters

19.2 Section Quiz. 1. If the [OH-] in a solution is 7.65  10-3M, what is the [H+] of this solution? a) 7.65  10-17M b) 1.31  10-12M c) 2.12M d) 11.88M

19.2 Section Quiz. 2. The [OH-] for four solutions is given below. Which one of the solution is basic? a) 1.0 x 10-6M b) 1.0 x 10-8M c) 1.0 x 10-7M d) 1.0 x 10-14M

19.2 Section Quiz. 3. What is the pH of a solution with a hydrogen-ion concentration of 8.5 x 10-2M? a) 12.93 b) 8.50 c) 5.50 d) 1.07

19.3 Strengths of Acids and Bases Lemons and grapefruits have a sour taste because they contain citric acid. Sulfuric acid is a widely used industrial chemical that can quickly cause severe burns if it comes into contact with skin. You will learn why some acids are weak and some acids are strong.

Strong and Weak Acids and Bases 19.3 Strong and Weak Acids and Bases An acid dissociation constant (Ka) is the ratio of the concentration of the dissociated (or ionized) form of an acid to the concentration of the undissociated (nonionized) form. Weak acids have small Ka values. The stronger an acid is, the larger is its Ka value.

Strong and Weak Acids and Bases 19.3 Strong and Weak Acids and Bases Strong acids are completely ionized in aqueous solution. Weak acids ionize only slightly in aqueous solution.

Strong and Weak Acids and Bases 19.3 Strong and Weak Acids and Bases In general, the base dissociation constant (Kb) is the ratio of the concentration of the conjugate acid times the concentration of the hydroxide ion to the concentration of the base. Strong bases dissociate completely into metal ions and hydroxide ions in aqueous solution. Weak bases react with water to form the hydroxide ion and the conjugate acid of the base.

Strong and Weak Acids and Bases 19.3

Calculating Dissociation Constants 19.3 How can you calculate an acid dissociation constant (Ka) of a weak acid? Ex. The dissociation constant, Ka, of ethanoic acid is calculated from the equilibrium concentrations of all of the molecules and ions in the solution.

19.3 Section Quiz. 1. H2S is considered to be a weak acid because it a) is insoluble in water. b) ionizes only slightly. c) is completely ionized. d) is dilute.

19.3 Section Quiz. 2. Calcium hydroxide, Ca(OH)2, is a strong base because it a) has a large Kb. b) has a small Kb. c) forms concentrated solutions. d) is highly soluble in water.

19.3 Section Quiz. 4. The Ka of three acids is given below. (1) 5.1  10–3 (2) 4.8  10–11 (3) 6.3  10–5 Put the acids in order from the strongest acid to the weakest acid. a) 1, 3, 2 b) 2, 3, 1 c) 3, 1, 2 d) 2, 1, 3

19.4 Neutralization Reactions Excess hydrochloric acid in the stomach can cause heartburn and a feeling of nausea. Antacids neutralize the stomach acid and relieve the pain of acid indigestion. You will learn what a neutralization reaction is.

Acid-Base Reactions 19.4 In general, the reaction of an acid with a base produces water and one of a class of compounds called salts. Reactions in which an acid and a base react in an aqueous solution to produce a salt and water are generally called neutralization reactions.

19.4 Acid-Base Reactions

Titration 19.4 The process of adding a known amount of solution of known concentration to determine the concentration of another solution is called titration. When an acid and base are mixed, the equivalence point is when the number of moles of hydrogen ions equals the number of moles of hydroxide ions.

19.4 Titration The solution of known concentration is called the standard solution. Indicators are often used to determine when enough of the standard solution has been added to neutralize the acid or base. The point at which the indicator changes color is the end point of the titration. Added base is measured with a buret. Acid solution with indicator Color change shows neutralization.

19.4 Section Quiz 1. When a neutralization takes place, one of the products is always a) carbon dioxide. b) a salt. c) sodium chloride. d) a precipitate.

19.4 Section Quiz 2. In a titration, 45.0 mL of KOH is neutralized by 75.0 mL of 0.30M HBr. What is the concentration of the KOH solution? a) 0.18M b) 0.60M c) 0.25M d) 0.50M

19.4 Section Quiz 3. How many moles of HCl are required to neutralize an aqueous solution of 2.0 mol Ca(OH)2? a) 0.5 mol b) 1.0 mol c) 2.0 mol d) 4.0 mol

19.4 Section Quiz 4. In which of the following neutralization titrations of 1-molar solutions of H2SO4 and NaOH will the equivalence point be reached at the very end of the additions? H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(aq) a) 200 mL of H2SO4 is slowly added to 100 mL of NaOH b) 200 mL of H2SO4 is slowly added to 200 mL of NaOH c) 100 mL of H2SO4 is slowly added to 200 mL of NaOH d) 100 mL of H2SO4 is slowly added to 100 mL of NaOH

19.5 19.5 Salts in Solution The chemical processes inside a living cell are very sensitive to pH. Human blood is normally maintained at a pH very close to 7.4. You will learn about chemical processes that ensure that the pH of blood is kept near 7.4.

Salt Hydrolysis 19.5 In salt hydrolysis, the cations or anions of a dissociated salt remove hydrogen ions from or donate hydrogen ions to water, causing solutions to be either acidic or basic. In general, salts that produce acidic solutions contain positive ions that release protons to water. Salts that produce basic solutions contain negative ions that attract protons from water.

Salt Hydrolysis 19.5 To determine whether a salt solution is acidic or basic, remember the following rules:

19.5 Salt Hydrolysis Vapors of the strong acid HCl(aq) and the weak base NH3(aq) combine to form the acidic white salt ammonium chloride (NH4Cl).

Salt Hydrolysis CH3COONa pH 5.3 NH4Cl pH 5.3 NaCl pH 7 19.5 Universal indicator solution has been added to each of these 0.10M aqueous salt solutions. A few drops of universal indicator solution have been added to each of these 0.10M aqueous salt solutions. The color of the indicator shows the following from left to right. Ammonium chloride (NH4Cl), is acidic (pH about 5.3), sodium chloride (NaCl) is neutral (pH 7), and sodium ethanoate (CH3COONa) is basic (pH about 8.7). CH3COONa pH 5.3 NH4Cl pH 5.3 NaCl pH 7

19.5 Buffers A buffer is a solution of a weak acid and one of its salts, or a solution of a weak base and one of its salts. The pH of a buffer remains relatively constant when small amounts of acid or base are added. The buffer capacity is the amount of acid or base that can be added to a buffer solution before a significant change in pH occurs.

19.5 Section Quiz. 1. Which of the following reactions would most likely yield a basic salt solution? a) strong acid + weak base b) weak acid + weak base c) strong acid + strong base d) weak acid + strong base

19.5 Section Quiz. 2. Choose the correct words for the spaces. A buffer can be a solution of a _________ and its _________. a) weak acid, salt b) strong acid, salt c) weak acid, conjugate base d) weak base, conjugate acid