Chapter 19

 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. 19.1

 Taste sour  Are electrolytes  Neutralize bases to form water and a salt  React with some metals to produce hydrogen gas  Change acid-base indicator colors 19.1

 Citrus fruits contain citric acid. Tea contains tannic acid. 19.1

 Taste bitter  Feel slippery  Are electrolytes  Neutralize acids to produce water and a salt  Change acid-base indicator colors 19.1

 Antacids use bases to neutralize excess stomach acid. The base calcium hydroxide is a component of mortar. 19.1

 Arrhenius said that acids yield hydrogen ions (H + ) as the only positive ion in solution. HCl  H + + Cl - H 2 SO 4  H 3 PO 4  Note: Arrhenius acid formulas start with H 19.1

 Arrhenius said that bases yield hydroxide ions (OH – ) as the only negative ion in solution. NaOH  Na + + OH - Ca(OH) 2  Note: Arrhenius bases end in -OH 19.1

◦ Which of the following acids and bases do not fit the definition of an Arrhenius acid or base?  NH 3  Ca(OH) 2  HCl  H 2 SO 4  CO 2  NaOH

◦ The Brønsted-Lowry theory defines an acid as a proton donor, and a base as a proton acceptor.  The Regents refers to this theory as “the other theory” 19.1

◦ Ammonia is a Base 19.1

 Identify the Bronsted-Lowry acids and bases in the following equations: NH 3 + H 2 O  NH OH - HCl + H 2 O  H 3 O + + Cl -

 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

 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. 19.2

◦ The reaction in which water molecules produce ions is called the self-ionization of water. 19.2

 In the self-ionization of water, a proton (hydrogen ion) transfers from one water molecule to another water molecule. 19.2

 The product of the concentrations of the hydrogen ions and hydroxide ions in water is called the ion- product constant for water (K w ) and equals Any aqueous solution in which [H + ] and [OH - ] are equal is neutral.

 An acidic solution is one in which [H + ] is greater than [OH - ]. 19.2

 Unrefined hydrochloric acid, commonly called muriatic acid, is used to clean stone buildings and swimming pools. 19.2

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

 Sodium hydroxide, or lye, is commonly used as a drain cleaner. 19.2

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

 A solution with a [H + ] greater than 1  10 –7 M has a pH less than 7.0 and is acidic.  A solution with a [H + ] = [OH - ] is neutral and has a pH of 7.  A solution with a [H + ] less than 1  10 –7 M has a pH greater than 7 and is basic. 19.2

◦ An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution.  Acid-Base Indicators shift at different pH’s resulting in color changes. 19.2

 Phenolphthalein changes from colorless to pink at pH 7–

 Universal Indicators 19.2

◦ pH Meters 19.2

 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. 19.3

 Strong acids are completely ionized in aqueous solution.  Weak acids ionize only slightly in aqueous solution. 19.3

 Strong bases dissociate completely into metal ions and hydroxide ions in aqueous solution. NaOH (aq)  Na + (aq) + OH - (aq)  Weak bases partially react with water to form the hydroxide ion H2OH2O

 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. 19.4

 The reaction of an acid with a base produces water and a salt.  A salt is an ionic compound whose (+) ion is not H + and whose (–) ion is not OH - These double replacement reactions are called neutralization reactions. 19.4

KOH + HCl  H 2 SO 4 + NaOH  H 3 PO 4 + Ca(OH) 2  Net neutralization:

19.4

◦ Adding a solution of known concentration to determine the concentration of another solution is called titration.  The solution of known concentration is called the standard solution.  Indicators are used to determine when enough of the standard solution has been added to neutralize the acid or base (end point).  A simple calculation can then find the unknown concentration 19.4

Acid solution with indicator Added base is measured with a buret. Color change shows neutralization. 19.4

 To solve titration problems the following equation is used: (ref table T) Be sure to use the molarity of the hydrogen and hydroxide ions and the not solutions!

◦ In solving titration problems, the concentrations of the hydrogen ions (H+) and hydroxide ions (OH-) must be used. These are not necessarily the same as the solution concentration!  What is the concentration of hydrogen or hydroxide ions in the following solutions?  1.5 M HCl  2.0 M H 2 SO 4  0.5 M Ca(OH) 2  O.1 M NaOH

◦ Calculate the molarity of an HCl solution if 15.0 mL of it is neutralized by 30.0 mL 0f 0.1 M NaOH.