The Chemistry of Acids and Bases

Part 1 - Objectives: What are characteristics of acids and bases? Examples of acids and bases? What pH ranges correspond to acidic, basic, and neutral solutions? What are the Bronsted Lowry and Arrhenius definitions of acids and bases? How do you name acids? What are characteristics of weak and strong acids and bases? Examples? What are neutralization reactions? How do they work?

Characteristics of Acids and Bases Have a sour taste Reacts with certain metals to produce hydrogen gas (H2) – corrodes metals React with carbonates (CO32-) and bicarbonates (HCO3) to produce CO2 gas Turn Litmus Paper RED pH is less than 7.00 Have a bitter taste Have a slippery feel React with metals to form hydroxides Reacts with ammonium salts Turn Litmus Paper BLUE pH is greater than 7.00 Strong bases are just as corrosive as acids Both acids and bases dissolve in water to form solutions that will conduct electricity. Acids and bases can react with each other

Arrhenius Definition of Acids and Bases An acid is any substance that adds hydrogen ions (H+) to a solution. A base is any substance that adds hydroxide (OH-) ions to a solution.

Why would a “H+” be called a proton? It is called a proton because hydrogen has lost its one and only electron, therefore now only consists of a single proton. What about bases that don’t have an “OH-” in them?

Arrhenius Acid

Arrhenius Base

Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water

Bronsted Lowry Definitions of Acids and Bases An acid is a proton donor. (Gives up H+ ions when placed in a solution) A base is a proton acceptor. (Will bond with H+)

Bronsted Lowry Definitions of Acids & Bases Continued: When an acid molecule dissolves in water, a hydrogen ion (H+) splits off, leaving the rest of the molecule with a negative charge. Examples: HCl will separate into H+ and Cl- ions Formic acid will separate into H+ and CHOO-

How do the Bronsted Lowry definitions work better than the Arrhenius? This explains why NH3 is a base even though it does not have OH-. NH3 accepts H+ from water, leaving NH4+ and OH-. When the molecule donates a proton (H+) to NH3, the water is acting as an acid. NH3 + H2O  NH4+ + OH-

Image Source: http://images. slideplayer. com/8/2296257/slides/slide_3

What is dissociation?

What does dissociation in solution look like?

Examples of Dissociation of Ions

Why are small changes in pH a big deal? The pH scale is a logarithmic scale that describes the concentration of [H+] in a solution [H+] and [OH]- are expressed in scientific notation because they exist in such LARGE numbers A solution with a pH of 2 is 1000 times more bsic than a solution with a pH of 5 (10 x 10 x 10)

pHooey! How does the [H+] and [OH-] of a solution relate to its pH? How can we determine the pH of a solution from [H+] or [OH-]? How can we determine the [H+] or [OH-] of a given solution using it’s pH?

pH is related to [H+] concentration by the formula: pH = -log[H+] [H+] = 10^(-pH)

Example 1: What is the pH of a 0.056 M HCl solution? 1) Determine [H+] in scientific notation from molarity 0.056 = 5.6 x 10-2 2) Plug and chug using formula pH = -log(5.6 x 10-2) pH = 1.25 There are no units for pH

Example 2: What would the [H+] concentration be in a solution with a pH of 3.75? 1)Set up formula 3.75 = -log(H+) 2)In calculator, enter “2nd (or shift) log” (pH) [H+] = 2nd Log (-3.75) 3) Write final concentration in scientific notation [H+] = 1.78 x 10-4

How is the concentration of H+ related to the concentration of OH-? In any solution, the product of [H+] and [OH-] is a constant number. (This number is called the “ion-product constant”.) [H+][OH-] = 1.0 x 10-14

Example 3: What would be the [H+] concentration of a solution that had a [OH-] of 2.5 x 10-4? 1)Set up formula [H+][2.5 x 10-4] = 1.0 x 10-14 2) Solve for “x” (2.5 x 10-4) (2.5 x 10-4) [H+] = 4.0 x 10-11

Classwork Friday March 11 World of Chemistry Textbook Problems Section 16.2 Review Questions 2,3,5 (Page 581)

How can we use the ion product constant to describe acidic and basic solutions? If [H+] > [OH-]  Solution is ACIDIC If [OH-] > [H+]  Solution is BASIC (ALKALINE) If [H+] = [OH-]  Solution is NEUTRAL

What is pOH? Direct measure of [OH-] pOH = -log[OH-] pH + pOH = 14.00

What is the relationship between pH and pOH?

How do we define weak and strong acids/bases? Source: http://image.slidesharecdn.com/acidsbasesandsalts-150128025312-conversion-gate01/95/acids-bases-and-salts-13-638.jpg?cb=1422414372

Figure: Extent of Dissociation for Weak and Strong Acid

Weak and Strong Acids and Bases Strong acids and bases will completely dissociate when placed in solution Weak acids and bases will only partially dissociate when placed in solution

Why are strong acids/bases considered to be good “electrolytes”, but weak acids/bases are not?

Why can we not say that a weak acid is a just a strong acid that’s been diluted?

Classwork Monday March 14: World of Chemistry Textbook Problems Chapter 16 Assessment (Pgs. 589 – 592) Problem #s: 32, 33, 34, 36

Homework: DUE FRIDAY (3/18) World of Chemistry Textbook – Chapter 16 Assessment Problems Problem #s: 22, 23, 24, 25, 35,

There are two basic types of acids: Binary Acids: acids that are made up of 2 elements, hydrogen and a nonmetal Oxyacids: acids that are made up of hydrogen and a polyatomic ion (many polyatomic ions contain the oxygen atoms)

How are binary acids named? Start with the word "hydro" (for our friend hydrogen) Change the second element's name so it ends with "-ic" End with the word "acid"

How are oxyacids named? DO NOT start with "hydro!" ("Hydro" is reserved for binary acids) Start with the full name of the polyatomic ion (nitrate, sulfate) and CHANGE the ending as follows: A) If the polyatomic anion ends with "-ate" change it to "-ic" (Think I ate something ic-ky) B) If the polyatomic anion ends with "-ite" change it to "-ous" (Think I took a b-ite of somethingdelici-ous) End with the word "acid"

How are acids named? An easy way to remember which goes with which… No Oxygen w/Oxygen An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

Acid Nomenclature Flowchart

Acid Nomenclature - Examples HBr (aq) H2CO3 H2SO3  hydrobromic acid  carbonic acid  sulfurous acid

Name ‘Em! HI (aq) HCl (aq) H2SO3 HNO3 HCH3COO HOCl

Name ‘Em! HI (aq) Hydroiodic acid HCl (aq) Hydrochloric acid H2SO3 Sulfuric acid HNO3 Nitric acid HCH3COO Acetic acid HOCl Hypochlorous acid

How are bases named? Name the metal CATION first; it keeps its name as listed in the Table of Ions. The polyatomic ion "hydroxide" (-OH) also keeps its name, and follows the cation. Examples: LiOH is "lithium hydroxide" Ca(OH)2 is "calcium hydroxide" NH4OH is "ammonium hydroxide"