Chemistry 19.2

Hydrogen Ions and Acidity 19.2 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 Hydrogen Ions from Water The reaction in which water molecules produce ions is called the self-ionization of water.

Hydrogen Ions from Water 19.2 Hydrogen Ions from Water In the self-ionization of water, a proton (hydrogen ion) transfers from one water molecule to another water molecule. The self-ionization of water. A proton (hydrogen ion) transfers from one water molecule to another water molecule. The result is one hydronium ion (H3O+) and one hydroxide ion (OH-).

Ion Product Constant for Water 19.2 Ion Product Constant for Water Ion Product Constant for Water How are [H+] and [OH-] related in an aqueous solution?

Ion Product Constant for Water 19.2 Ion Product Constant for Water 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.

Ion Product Constant for Water 19.2 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).

Ion Product Constant for Water 19.2 Ion Product Constant for Water An acidic solution is one in which [H+] is greater than [OH-].

Ion Product Constant for Water 19.2 Ion Product Constant for Water Unrefined hydrochloric acid, commonly called muriatic acid, is used to clean stone buildings and swimming pools. Acids and bases have many uses in the home and in industry. a) Unrefined hydrochloric acid, commonly called muriatic acid, is used to clean stone buildings and swimming pools. b) Sodium hydroxide, or lye, is commonly used as a drain cleaner. Predicting How will each chemical affect the hydrogen-ion and hydroxide-ion concentration of an aqueous solution?

Ion Product Constant for Water 19.2 Ion Product Constant for Water A basic solution is one in which [H+] is less than [OH]. Basic solutions are also known as alkaline solutions.

Ion Product Constant for Water 19.2 Ion Product Constant for Water Sodium hydroxide, or lye, is commonly used as a drain cleaner. Acids and bases have many uses in the home and in industry. a) Unrefined hydrochloric acid, commonly called muriatic acid, is used to clean stone buildings and swimming pools. b) Sodium hydroxide, or lye, is commonly used as a drain cleaner. Predicting How will each chemical affect the hydrogen-ion and hydroxide-ion concentration of an aqueous solution?

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Solve Problem 10 with the help of an interactive guided tutorial. for Sample Problem 19.1 Problem Solving 19.10 Solve Problem 10 with the help of an interactive guided tutorial.

19.2 The pH Concept The pH Concept How is the hydrogen-ion concentration used to classify a solution as neutral, acidic, or basic?

19.2 The pH Concept The pH of a solution is the negative logarithm of the hydrogen-ion concentration.

19.2 The pH Concept Calculating pH

19.2 The pH Concept 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.

19.2 The pH Concept The hydrogen-ion concentrate of a solution is used to classify the solution as acidic, neutral, or basic. INTERPRETING GRAPHS a. Identify What is [H3O+] in a neutral solution? b. Describe How does [H3O+] compare with [OH-] in an acidic solution? c. Compare and Contrast In terms of ion concentrations, how are basic solutions different from acidic solutions?

19.2 The pH Concept

19.2 The pH Concept Calculating pOH

pH and Significant Figures 19.2 The pH Concept pH and Significant Figures The pH scale shows the relationship between pH and the hydrogen-ion concentration. Interpreting Diagrams What happens to [H+] as pH increases?

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Solve Problem 12 with the help of an interactive guided tutorial. for Sample Problem 19.2 Problem Solving 19.12 Solve Problem 12 with the help of an interactive guided tutorial.

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Solve Problem 14 with the help of an interactive guided tutorial. for Sample Problem 19.3 Problem Solving 19.14 Solve Problem 14 with the help of an interactive guided tutorial.

19.2 Measuring pH Measuring pH What is the most important characteristic of an acid-base indicator?

19.2 Measuring pH An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution.

Phenolphthalein changes from colorless to pink at pH 7–9. 19.2 Measuring pH Phenolphthalein changes from colorless to pink at pH 7–9. Acid-base indicators respond to pH changes over a specific range. Phenolphthalein changes from colorless to pink at pH 7–9.

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Solve Problem 15 with the help of an interactive guided tutorial. for Sample Problem 19.4 Problem Solving 19.15 Solve Problem 15 with the help of an interactive guided tutorial.

19.2 Measuring pH Acid-Base Indicators

19.2 Measuring pH Indicators change color at a different pH. INTERPRETING GRAPHS a. Identify Which indicator changes color in a solution with a pH of 2? b. Compare and Contrast What do you notice about the range over which each indicator changes color? c. Apply Concepts Which indicator would you choose to show that a solution has changed from pH 3 to pH 5?

Universal Indicators 19.2 Measuring pH You can find acidic and basic substances in your home. a) Universal indicator solution has been added to solutions of known pH in the range from 1 to 12 to produce a set of reference colors. b) Universal indicator has been added to samples of vinegar, soda water, and ammonia solution. Interpreting Photographs Use the reference colors to assign pH values to vinegar, soda water, and ammonia solution.

19.2 Measuring pH pH Meters 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?

19.2 Section Quiz. 19.2.

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

19.2 Section Quiz. 2. The [OH-] for four solutions is given below. Which one of the solution is basic? 1.0 x 10-6M 1.0 x 10-8M 1.0 x 10-7M 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? 12.93 8.50 5.50 1.07

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