Chemistry Jacqueline P. Hancock, B.S., M.Ed Acids, Bases, & Salts Chemistry Jacqueline P. Hancock, B.S., M.Ed

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 Acids taste sour, will change the color of an acid-base indicator, and can be strong or weak electrolytes in aqueous solution. Citrus fruits contain citric acid. Tea contains tannic acid. Bases Bases taste bitter, feel slippery, will change the color of an acid-base indicator, and can be strong or weak electrolytes in aqueous solution. Antacids use bases to neutralize excess stomach acid. Calcium hydroxide is a component of mortar.

Properties of Acids & Bases Sour taste Turn blue litmus RED React with metals to produce hydrogen gas React with carbonates to produce carbon dioxide Strong or weak electrolytes in (aq) sol Bases Bitter taste Turn red litmus Blue Slippery to touch Strong or weak electrolytes in (aq) sol

Three ways to define acids and bases Arrhenius Brønsted-Lowry Lewis

Arrhenius Acids and Bases 19.1 Arrhenius Acids and Bases Arrhenius Acids and Bases Acids -produce hydrogen ions (H+) in aqueous solution. Bases -produce hydroxide ions (OH–) in aqueous solution

Arrhenius Acids and Bases 19.1 Arrhenius Acids and Bases Hydrochloric Acid Hydrochloric acid is actually an aqueous solution of hydrogen chloride. Hydrogen chloride forms hydronium ions, making this compound an acid.

Arrhenius Acids and Bases pg 588 19.1 Arrhenius Acids and Bases pg 588 Arrhenius Acids Monoprotic acids-contain one ionizable hydrogen Diproti acids -contain two ionizable hydrogens Triprotic acids- contain three ionizable hydrogens

Common Acids HCl Hydrochloric acid HNO3 Nitric acid H2SO4 Sulfuric acid H2CO3 Carbonic acid HC2H3O2 Acetic acid H3PO4 Phosphoric acid

Arrhenius Acids and Bases 19.1 Arrhenius Acids and Bases Arrhenius Bases Hydroxide ions are one of the products of the dissolution of an alkali metal in water.

Arrhenius Acids and Bases pg 589 19.1 Arrhenius Acids and Bases pg 589

Common Bases NaOH Sodium Hydroxide KOH Potassium Hydroxide Ca(OH)2 Calcium Hydroxide NH3 Ammonia Al(OH)3 Aluminum Hydroxide Mg(OH)2 Magnesium Hydroxide

Brønsted-Lowry Acids and Bases 19.1 Brønsted-Lowry Acids and Bases Brønsted-Lowry Acids and Bases Acid is a hydrogen-ion donor Base as a hydrogen-ion acceptor.

Brønsted-Lowry Acids and Bases 19.1 Brønsted-Lowry Acids and Bases Why Ammonia is a Base Ammonia dissolves in water to form ammonium ions and hydroxide ions. In this reaction, the water molecule donates a hydrogen ion to the ammonia molecule. Explaining Why is ammonia not classified as an Arrhenius base?

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.

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. Amphoteros-Greek word meaning partly one and partly the other.

Brønsted-Lowry Acids and Bases pg 591 19.1 Brønsted-Lowry Acids and Bases pg 591

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?

Lewis Acids and Bases Lewis Acids and Bases 19.1 Lewis Acids and Bases Lewis Acids and Bases Acid accepts a pair of electrons to form a covalent bond Base donates a pair of electrons to form a covalent bond

for Conceptual Problem 19.1 Identify the reactants as either an acid or base Identify the Lewis acid and Lewis base in each reaction c. KOH + HBr KBr + H2O d. HCl + H2O H3O+ +Cl-

Identify the Acids and Bases in the reactants only BF3 + F- BF4- H2O + NH3 NH4+ + OH- HCl + H2O H3O+ +Cl- Ag+ +2NH3 [Ag(NH3)2]+

19.1 Lewis Acids and Bases

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. 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?

Hydrogen Ions from Water 19.2 Hydrogen Ions from Water Self ionization of water, a proton (hydrogen ion) transfers from one water molecule to another water molecule. Simple dissociation 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-).

Self- Ionization of Water (Dissociation) H2O Highly polar & in Constant motion Pure water contains small concentrations of H+ & OH- as well as H2O molecules High energy collisions allows transfer Resulting in H3O+ and OH-

Ion Product Constant for Water 19.2 Ion Product Constant for Water 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

@ 25oC Equilibrium [H+] is 1x10-7 M Equilibrium [OH-] is 1x10-7 M Therefore the ion concentrations in pure water are equal making it Neutral

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

Acid or Base? To determine whether a solution is acidic or alkaline(basic) Use the exponent value for the ion given. If [OH-] ….. Find the [H+] Acid pH < 7.0 [H+] > 1x10-7M Neutral pH= 7.0 [H+] = 1x10-7M Basic pH>7.0 [H+] < 1x10-7M

Ion Concentration To determine the ion concentration use the Ion-product constant for water Rearrange the formula to isolate the unknown variable (solve for the missing variable) Plug in the known values Ion-Product Constant Formula

Practice Problems Classify as acidic, basic, or neutral [H+]= 6x10-12 M [OH-] = 3.0x10-2 M [H+] = 2.0x10-7 M [OH-]= 1.0x10-7 M Base -12 < -7 Base -14/-2=-12 -12< -7 Acid 2x10-7 > 1x10-7 Neutral =

Acid pH < 7.0 [H+] > 1x10-7M Neutral pH= 7.0 [H+] = 1x10-7M Basic pH>7.0 [H+] < 1x10-7M

Quiz 19-2 1. If the [H+] in a solution is 1.0x10-9M, what is the [OH-] of this solution? 2. If the hydroxide-ion concentration of an aqueous solution is 1x10-5M, what is the [H+] in the solution? Is the solution acidic, basic, or neutral?

pH 1909 Danish scientist SØren SØrensen developed pH scale of 0-14 (acid to base) pH is the negative logarithm of the hydrogen-ion concentration of a solution pH= -log[H+] pOH= -log[OH-] pH + pOH = 14

pH

pH meter

Calculating pH Calculation pH from [H+] pH= -log[H+] Ex. [H+] = 1x10-8 Find the pH of each solution [H+] =1x10-4M [H+] = 0.0015M What are the pH values of the following solutions, based on their hydrogen-ion concentrations? [H+] = 1x10-12M [H+]= 0.045M

Calculating [H+] from pH Calculate [H+] for each solution pH= 5.0 Original formula: pH = -log[H+] Derived formula: antilog(-pH) Example: pH= 6.38 =antilog(-6.38) = 4.17 x10-7 M Calculate [H+] for each solution pH= 5.0 pH= 12.83 pH= 4.0 pH= 11.55

Practice Problems Calculating pH from [OH-] First find [H+] Use Kw formula Use pH= -log[H+] First find [H+] Second find –log[H+] -log(H+ value) Answer should be positive!!! Calculate the pH of the solution [OH-]= 4.3x10-5M [OH-]= 4.5x10-11M [H+] = 5.0x10-5M [H+]= 8.3x10-10M

Homework … [H+] pH [OH-] pOH Acid or Base 1x10-4 12 5.6 2.6x10-8 9.8 5.0x10-3 4.23 4.35 1.85x10-7 4.0x10-11 3.5 8.75 6.78 x10-9 .05

Acid-Base Indicators Know Figure 19.2 An indicator(Hln) undergoes dissociation in a known pH range Changes colors in different solutions Limits of liquid indicators Optimal temp 250C Color sol. Can distort Dissolved salts can affect dissociation Paper indicators pH meters Know Figure 19.2 Thymol Blue Bromphenol Blue Bromcresol green Methyl Red Alizarin Bromthymol Blue Phenol Red Phenolphtalein Alizarin yellow R