The Chemistry of Acids and Bases Chemistry I – Chapter 19 To play the movies and simulations included, view the presentation in Slide Show Mode.

Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas And salt. React with carbonates and bicarbonates to produce carbon dioxide gas Bases Have a bitter taste. Feel slippery. Many soaps contain bases.

Example: Mg + 2HCl  MgCl2 + H2

Some Properties of Acids Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) Taste sour Corrode metals Electrolytes React with bases to form a salt and water pH is less than 7 Turns blue litmus paper to red “Blue to Red A-CID”

Acid Nomenclature Review No Oxygen w/Oxygen An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

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

HI (aq) Hydroiodic Acid HCl (aq) Hydrochloric Acid H2SO4 Sulfuric Acid Name ‘Em! HI (aq) Hydroiodic Acid HCl (aq) Hydrochloric Acid H2SO4 Sulfuric Acid HNO3 Nitric Acid HPO4 Phosphoric Acid HCO3 Carbonic Acid HOH Water! (Dihydrogen Monoxide)

Some Properties of Bases Produce OH- ions in water Taste bitter, chalky Are electrolytes Feel soapy, slippery React with acids to form salts and water pH greater than 7 Turns red litmus paper to blue “Basic Blue”

Some Common Bases NaOH sodium hydroxide lye KOH potassium hydroxide liquid soap Ba(OH)2 barium hydroxide stabilizer for plastics Mg(OH)2 magnesium hydroxide Milk of magnesia Al(OH)3 aluminum hydroxide Maalox (antacid)

Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H+ ions (or hydronium ions H3O+) Bases – produce OH- ions (problem: some bases don’t have hydroxide ions!)

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

A “proton” is really just a hydrogen atom that has lost it’s electron! A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor base acid

Conjugate Pairs

A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor conjugate base base acid conjugate acid

Acids & Base Definitions Definition #3 – Lewis Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair

Lewis Acid/Base Reaction

Neutralization Acid+Base=Salt+Water Ex: HCl + NaOH  NaCl + H2O Ca(OH)2 + HCl  CaCl2 + H2O

Complete Acid/Base Worksheet on page 10 and 11

The pH scale is a way of expressing the strength of acids and bases The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion. Under 7 = acid 7 = neutral Over 7 = base

pH of Common Substances

(Remember that the [ ] means Molarity) Calculating the pH pH = - log [H+] (Remember that the [ ] means Molarity) Example: If [H+] = 1 X 10-10 pH = - log 1 X 10-10 pH = - (- 10) pH = 10 Example: If [H+] = 1.8 X 10-5 pH = - log 1.8 X 10-5 pH = - (- 4.74) pH = 4.74

pH = - log(0.15) = 0.82 pH = - log(3.00X10-7) = 6.52 Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10-7 M solution of Nitric acid pH = - log(0.15) = 0.82 pH = - log(3.00X10-7) = 6.52

pH calculations – Solving for H+ If the pH of Coke is 3.12, [H+] = ??? 10-pH = [H+] [H+] = 10-3.12 = 7.6 x 10-4 M

pH calculations – Solving for H+ A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? 10-8.5 = [H+] 3.16 X 10-9 M = [H+]

pOH Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH. pOH looks at the perspective of a base pOH = - log [OH-] Since pH and pOH are on opposite ends, pH + pOH = 14

=10 0 =10 0 pH [H+] [OH-] pOH

[H+], [OH-] and pH What is the pH of the 0.0010 M NaOH solution? [OH-] = 0.0010 M (or 1.0 X 10-3 M) pOH = - log[OH-] = -log 0.0010 pOH = 3 pH = 14 – 3 = 11

The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater? [H+] = 10 -4.82 [H+] =1.51X10 -5 M The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood? pOH = -log [2.5 x 10-7 ] pOH = 6.6 pOH + pH = 14 pH = 14 – pOH = 7.4

[OH-] [H+] pOH pH 1.0 x 10-14 [OH-] 10-pOH 1.0 x 10-14 -Log[OH-] [H+] -Log[H+] 14 - pH pH

Calculating [H+], pH, [OH-], and pOH Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 1.0 M and (b) 0.0024 M. Calculate the pH, [H+], pH, pOH, and [OH-] of the two solutions at 25°C. Solution 1: pH = -log [H+] = -log(1.0) = 0 10-pH = [H+] = 10-0 = 1 pOH = 14 - pH = 14 – 0 =14 10-pOH = [OH-] = 10-14

Calculating [H+], pH, [OH-], and pOH Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 1.0 M and (b) 0.00240 M. Calculate the pH, [H+], pH, pOH, and [OH-] of the two solutions at 25°C. Solution 2: pH = -log [H+] = -log(0.0024) = 2.62 10-pH = [H+] = 10-2.6 = 0.00240 pOH = 14 - pH = 14 – 2.62 = 11.4 10-pOH = [OH-] = 10-11.4 = 3.98X10 -12 M

Calculating [H+], pH, [OH-], and pOH Problem 2: What is the [H+], pOH, and [OH-] of a solution with pH = 3.67? Is this an acid, base, or neutral? 10-pH = [H+] = 10-3.67 = 0.000214 M pOH = 14 - pH = 14 – 3.67 = 10.3 10-pOH = [OH-] = 10-10.3 = 5.01X10 -11 M

Complete pH problems on page 15

pH testing There are several ways to test pH Blue litmus paper (red = acid) Red litmus paper (blue = basic) pH paper (multi-colored) pH meter (7 is neutral, <7 acid, >7 base) Universal indicator (multi-colored) Indicators like phenolphthalein Natural indicators like red cabbage, radishes

Paper testing Paper tests like litmus paper and pH paper Put a stirring rod into the solution and stir. Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper Read and record the color change. Note what the color indicates. You should only use a small portion of the paper. You can use one piece of paper for several tests.

pH paper

pH meter Tests the voltage of the electrolyte Converts the voltage to pH

pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage

ACID-BASE REACTIONS Titrations Setup for titrating an acid with a base

Titration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called NEUTRALIZATION.

If it is a 1:1 Ratio between H+ and OH- in their formulas in a neutralization you can use the dilution equation Mbase X Vbase = Macid X Vacid HCl + NaOH  H2O + NaCl 1:1 ratio!

If it is not a 1:1 molar ratio between H+ and OH- in their formulas (ignore coefficients for this!), then you must MULTIPLY the molarity of the acid by the # of H+ ions over the # of OH- ions in the acid and base formulas before you solve the dilution equation. Ex. 2NaOH + H2SO4  Na2SO4 + 2H2O MULTIPLY the molarityacid by 2/1 or 2. Mbase X Vbase = 2Macid X Vacid

LAB PROBLEM #1: Titration Problem. Given: HCl + NaOH  H2O + NaCl 35.62 mL of NaOH is neutralized with 25.2 mL of 0.0998 M HCl by titration to an equivalence point. What is the concentration of the NaOH? 1:1 Ratio between acid and base! Mbase X Vbase = Macid X Vacid Mbase X 35.62mL = 0.0998M X 25.2mL Mbase = 0.0998M X 25.2mL = 0.0706 M 35.62mL

LAB PROBLEM #2: Titration Problem. Given: 2H3PO4 + 2KOH  3H2O + 2KPO4 35.62 mL of KOH is neutralized with 25.2 mL of 0.0998 M H3PO4 by titration to an equivalence point. What is the concentration of the NaOH? 3:1 RATIO -- MULTIPLY THE MOLARITY OF THE ACID BY 3 BEFORE SOLVING!! Mbase X Vbase = 3Macidx Vacid Mbase X 35.62mL = 3(0.0998M) X 25.2mL Mbase = 3(0.0998M) X 25.2mL = 0.212 M 35.62mL

COMPLETE TITRATION PROBLEMS on page 12

Oxidation - reduction Chemistry I – Chapter 20 Oxidation is loss of electrons Reduction is gain of electrons Oxidation is always accompanied by reduction The total number of electrons is kept constant Oxidizing agents oxidize and are themselves reduced Reducing agents reduce and are themselves oxidized

Oxidation numbers Oxidation number is the number of electrons gained or lost by the element in making a compound Metals are typically considered more 'cation-like' and would possess positive oxidation numbers, while nonmetals are considered more 'anion-like' and would possess negative oxidation numbers.

Loss of Electrons is Oxidation Gain of Electrons is Reduction Memory Device LEO the lion says GER Loss of Electrons is Oxidation Gain of Electrons is Reduction

Predicting oxidation numbers Oxidation number of atoms in element is zero in all cases Oxidation number of element in monatomic ion is equal to the charge Sum of the oxidation numbers in a compound is zero Sum of oxidation numbers in polyatomic ion is equal to the charge F has oxidation number –1 H has oxidation no. +1 Oxygen is usually –2.

Position of element in periodic table determines oxidation number G1A is +1 G2A is +2 G3A is +3 (some rare exceptions) G5A are –3 in compounds with metals G6A below O are –2 in binary compounds with metals, H or NH4+. G7A elements are –1 in binary compounds with metals, H or NH4+ or with a heavier halogen.

Identifying reagents Those elements that tend to give up electrons (metals) are typically categorized as reducing agents and those that tend to accept electrons (nonmetals) are referred to as oxidizing agents.

Iron can reduce Cu2+ to Cu The iron nail reduces the Cu2+ ions and becomes coated with metallic Cu. At the same time, the intensity of the blue color diminishes due to loss of Cu2+ ions from solution.

Nuggets of redox processes Where there is oxidation there is always reduction Oxidizing agent Reducing agent Is itself reduced Is itself oxidized Gains electrons Loses electrons Causes oxidation Causes reduction

Identify redox by change in oxidation numbers: follow the flow of electrons Reducing agent increases its oxidation number Oxidizing agent decreases its oxidation number

In reactions with metals, nonmetals are always oxidizers (oxidizing agents that are themselves reduced) Reactions of elements are always redox The nonmetal gains electrons, becomes a negative ion The metal loses electrons, becomes a positive ion

Oxidation number method What goes up must come down… Sum of the changes in oxidation numbers in any process is zero

Assign oxidation numbers Use the rules of oxidation numbers Element is zero Monatomic ion: oxidation number is same as charge Oxide is -2 +2 -1 +7

Identify oxidized and reduced Mn is reduced from +7 to +2 Net gain of 5 electrons Br is oxidized from -1 to 0 Net loss of 1 electron +2 -1 +7

Complete Oxidation/Reduction Problems on page 13