Acids and Bases Chapter 14 and Section 15.2

Objectives Identify key terms and concepts. Identify an acid and a base using Bronstead- Lowery Acid/Base Theory. Identify a Lewis acid and base. Explain the acid-base properties of water. Name acids and bases. Explain the properties of acids, bases, and salts. Explain how a buffer works. Identify acid-base conjugate pairs. Determine the products of a neutralization reaction.

Objectives Calculate the pH and hydronium concentration of a solution. Calculate acid/base ionization constants. Determine the percent ionization for an acid or a base. Explain how a salt will affect the pH of a solution. Identify the acid-base properties of an oxide and hydroxide. Determine the relative strength of an acid-base conjugate pair.

Objectives Explain how a buffer works and how to prepare a buffer system for a specific pH. Calculate the pH of a buffer solution. Calculate the equivalence point for acid-base titrations.

Acids Cause litmus paper to turn red Tastes sour Dissolves metals like Zn and Fe to produce hydrogen gas

Acids For an acid containing a hydrogen and an anion: use the prefix hydro and change the –ide of the nonmetal to –ic and add the word acid. HCl = Hydrogen Chloride is Hydrochloric Acid For an acid containing a polyatomic ion, name the anion after the polyatomic ion, changing the –ate to –ic or the –ite to –ous and add the word acid. HNO3 = Hydrogen Nitrate is Nitric Acid HNO2 = Hydrogen Nitrite is Nitrous Acid

Write the Name or Formula for each of the Following Acids H2SO4 HF HBr H3PO4 Acetic acid Carbonic Acid Hydroiodic Acid Phosphorous Acid

Acids Strong Acids Weak Acids Strong electrolytes that will completely ionize in water H2SO4  H+ + HSO4- Only a few strong acids HCl, HNO3, H2SO4, HBr, HI, HClO4 Weak Acids Will only partially ionize in water (weak electrolytes) Most acids are weak HF, acetic acid, citric acid, salicylic acid, oxalic acid HF + H2O ↔ F- + H3O+

Bases Cause litmus paper to turn blue Tastes bitter Name like a normal compound Ca(OH)2  Calcium Hydroxide NaOH  Sodium Hydroxide

Bases Strong Bases Weak Bases Strong electrolytes that will completely ionize in water NaOH  Na+ + OH- LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 Weak Bases Weak Bases do not furnish OH- ions by dissociation. Instead, they react with water to generate OH- ions. Weak electrolytes NH3 + H2O ↔ NH4 + OH-

Acids Bases

Acid-Base Indicators pH meters Litmus and pH paper Universal Indicator Phenolphthalein Methyl Red Thymol Blue

Percent Ionization Percent Ionization The higher the percent ionization, the stronger the acid Ionized acid concentration at equilibrium Initial concentration of acid % Ionization = x 100

The pH of a 0. 30M solution of acetic acid is 2. 79 The pH of a 0.30M solution of acetic acid is 2.79. What is the percent ionization?

The pH of a 0. 15M solution of hydrofluoric acid is 3. 25 The pH of a 0.15M solution of hydrofluoric acid is 3.25. What is the percent ionization?

The Arrhenius Theory Acid A substance that ionizes into hydrogen ions and anions in water HCl  H+ + Cl- Base A substance that releases hydroxide ions in water NaOH  Na+ + OH- Stated the reaction of an acid and a base will produce salt and water HCl + NaOH  NaCl + H2O

Problems with the Arrhenius Theory A hydrogen ion does not exist in water. Instead, the H+ ion attaches to one of the oxygen loan pairs of electrons on water to make a hydronium ion. Does not explain the basicity of ammonia of where the hydroxide ion comes from when ammonia is dissolved in an aqueous solution. NH3 + H2O  NH4 + OH- Applies only to reactions in aqueous solution (water).

Bronstead-Lowry Acid-Base Theory Proton Donor HCl + H2O  H3O+ + Cl- Base Proton Acceptor NH3 + H2O  NH4 + OH-

Identify the acid and base in the following reactions using Bronstead-Lowery Acid/Base Theory S2- + H2O  OH- + HS- PO43- + HNO3  NO3- + HPO42- C2O42- + HC2H3O2  HC2O4- + C2H3O2- HCO2H + OH-  CO2H- + H2O HCl + H2O  H3O + Cl-

Lewis Acids and Bases Lewis Acid Lewis Base Accepts a pair of electrons Lewis Base Donates a pair of electrons Much more general description of acids and bases The reaction does not have to involve the transfer of a hydrogen.

Identify the acid and base in the following reactions using Lewis acid/base Theory Cr3+ + 6H2O  Cr(H2O)63+ BeCl + H2O  BeCl(H2O)2 AlCl3 + CH3Cl  AlCl3CH3Cl SO2 + H2O SO3H2 BF3 + H2O  BF3H2O

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The pH scale Measures how basic or acidic a solution is Measures the concentration of hydronium present pH = -log[H3O+] pOH = -log[OH-] pH + pOH = 14 pH > 7, basic solution pH < 7, acidic solution pH = 7, neutral solution

What is the pH of the solutions containing the following concentrations of hydronium ions? What is the pOH of the solutions? 1x10-2 M 3.5x10-3 M 4x10-7 M 2x10-6 M 1x10-9 M

What is the hydronium and hydroxide ion concentrations for the solutions with the following pH? 1 6.9 4.7 13 9.2

Reactions of Acids and Bases Neutralization The reaction between a strong acid and a strong base with produces salt and water Double replacement reaction Salt An ionic compound that does not have H+ or OH- ions

Complete the following neutralization reactions Ca(OH)2 + HNO3  NH3 + H2SO4  Mg(OH)2 + H3PO4  NaOH + HC2H3O4 

Neutralization Reactions – Gas Forming If a gas forms, such as CO2 (from H2CO3), SO2 (from H2SO3), or NH3 (from NH4OH), it is called a gas forming reaction. NH4Br + KOH  HC2H3O2 + NaHCO3  HCl + LiHSO3 

Molecular Structure and the Strength of Acids Properties affecting the strength of acids Properties of the solvent Temperature Molecular structure of the binary acid Ionization The stronger the bond, the weaker the acid Going down a column on the periodic table, the size of the molecule increases, the bond strength decreases, and the strength of the acid increases. Higher the polarity of the molecule, the stronger the acid Going across a row of the periodic table, the electronegativity increases, the bond polarity increases, and the acid strength increases.

Molecular Structure and the Strength of Acids Hydrohalic Acids Acids containing a halogen The bond strength in these acids has a larger influence over the strength of the acid than the polarity of the molecule HF < HCl < HBr < HI

Molecular Structure and the Strength of Acids Oxoacids Contain H, O, and a third element Oxoacids with different central atoms from the same group on the periodic table with the same oxidation number As the electronegativity of the central atom increases, the acid strength increases Oxoacids with the same central atom but different numbers of attached groups As the oxidation number of the central atom increases, so does the acid strength HClO4 > HClO3 > HClO2 > HClO

Which of the following acids has the greatest strength? NH3 or PH3 HI or H2Te HSO3- or H2SO3 H3AsO3 or H3AsO4 HSO4- or HSeO4-

Conjugate Acids and Bases Conjugate Acid-Base Pair Pair of molecules or ions related by the loss of gain of a H+

Conjugate Acids and Bases

Conjugate Acids and Bases Properties of conjugate acid-base pairs If an acid is strong, its conjugate base is very weak. H3O+ is the strongest acid that can exist in water. Acids stronger than H3O+ will react completely with water to form H3O+ and a conjugate base. Acids weaker than H3O+ will react with water to a lesser extent to produce H3O+ and a conjugate acid (reversible reaction). OH- is the strongest base that can exist in water. Bases stronger than OH- will react completely with water to produce OH- and a conjugate acid.

Identify the conjugate acid-base pairs in the following reactions NH3 + H2O  NH4+ + OH- HCl + H2O  H3O + Cl- H2O + CH3CO2H  H3O + CH3CO2- H2O + H2SO4  H3O+ + HSO4-

Identify the conjugate acid-base pairs in the following reactions S2- + H2O  OH- + HS- PO43- + HNO3  NO3- + HPO42- C2O42- + HC2H3O2  HC2O4- + C2H3O2- HCO2H + OH-  CO2H- + H2O

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Acid-Base Properties of Salts Strong electrolytes that dissolve completely in water NaCl, NaNO3, KBr Salt Hydrolysis The reaction of an anion or a cation of a salt, or both, with water. Affects the pH of water

Acid-Base Properties of Salts Salts that produce neutral solutions CaCl2(aq) Ca+(aq) + 2Cl-(aq) Salts that produce basic solutions CH3COONa(aq) Na+(aq) + CH3COO-(aq) CH3COO- (aq) + H2O(l) OH-(aq) + CH3COOH(aq) Salts that produce acidic solutions NH4Cl(aq) NH4+(aq) + Cl-(aq) NH4+(aq) + H2O(l) NH3 (aq) + H+(aq)

Acid-Based Properties of Salts Kb > Ka, then the solution is basic because the anion will hydrolyze to a great extent than the cation Kb < Ka, then the solution will be acidic because cation hydrolysis will be greater than anion hydrolysis Kb = Ka, then the solution will be near neutral pH

Predict weather a salt solution is acids, basic, or neutral? NaCN LiF KNO3 NaHCO3 NaC7H5O2

Acid-Base Properties of Oxides Basic oxides will form bases when reacted with water. Na2O + H2O  NaOH Acidic oxides will form an acid when reacted with water. SO3 + H2O  H2SO4 Reactions between acidic/basic oxides and acids/bases produce salt and water. Na2O + 2HCl  2NaCl + H2O SO3 + 2LiOH  Li2SO4 + H2O Amphoteric oxides can act as both an acid and a base.

Acidic, Basic, and Amphoteric Oxides

Acid-Base Properties of Hydroxides Alkali and alkaline metal hydroxides are basic – Except for Be(OH)2 Many metal hydroxides are amphoteric Al(OH)3, Sn(OH)2, Pb(OH)2, Cr(OH)2, Cu(OH)2, Zn(OH)2, Cd(OH)2 Sn(OH)2 + 2H+  Sn2+ + H2O Sn(OH)2 + 2OH-  Sn(OH)42- All amphoteric hydroxides are insoluble.

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Acid Base Properties of Water Can act as either an acid or a base. Base H2O(l) + CH3CO2H (aq) H3O+(aq) + CH3CO2- (aq) Acid NH3 (aq) + H2O(l) NH4+ (aq) + OH- (aq) Water can undergo ionization to a small extent. H2O(l) H+(aq) + OH-(aq) During this ionization, water can act as both the acid and the base. H2O(l) + H2O(l) H3O+(aq) + OH-(aq)

Ionization Constants Acid Ionization Constant Equilibrium constant for the ionization of an acid H2O(l) + HA(aq) H3O+(aq) + A-(aq) Base Ionization Constant Equilibrium constant for the ionization of a base NH3 (aq) + H2O(l) NH4+ (aq) + OH- (aq) [H3O+][A-] [HA] Ka = [NH4+ ][OH-] [NH3] Kb =

Ionization Constants For conjugate acid-base pairs, the ionization constants are related using the following equation CH3COOH (aq) H+(aq) + CH3COO- (aq) CH3COO- (aq) + H2O(l) CH3COOH (aq) + OH- (aq) H2O(l) H+(aq) + OH- (aq) Kw = KaKb

HC2H3O2(aq) C2H3O2-(aq) + H+(aq) Calculate the pH of a 0.5M solution of acetic acid in aqueous solution: HC2H3O2(aq) C2H3O2-(aq) + H+(aq)

Calculate the pH of a 0.65M solution of HF in aqueous solution: HF(aq) F-(aq) + H+(aq)

What is the pH of a 0.25M solution of ammonia?

The pH of a 0. 30M solution of acetic acid is 2. 79 The pH of a 0.30M solution of acetic acid is 2.79. Calculate the Ka of the acid?

The pH of a 0. 15M solution of hydrofluoric acid is 3. 25 The pH of a 0.15M solution of hydrofluoric acid is 3.25. Calculate the Ka of the acid?

The pH of a 0. 75M solution of methylamine, CH3NH2, is 8. 78 The pH of a 0.75M solution of methylamine, CH3NH2, is 8.78. Calculate the Kb of the base?

Diprotic and polyprotic acids Produce more than 1 hydrogen per mole when ionized. Ionization occurs in several steps. H2SO3(aq) H+(aq) + HSO3-(aq) HSO3-(aq) H+(aq) + SO32-(aq)

When sulfurous acid is dissolved in water, it dissociates in two steps When sulfurous acid is dissolved in water, it dissociates in two steps. Calculate the concentrations of all species present at equilibrium in a 0.25M solution. H2SO3(aq) H+(aq) + HSO3-(aq) HSO3-(aq) H+(aq) + SO32-(aq)

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Conjugate Acids and Bases

Buffers Buffer solutions resist changes in pH when small amounts of acids or bases are added Buffers are made of a weak acid or base and it’s salt (acid-base conjugate pair) Buffering Capacity

Buffers https://www.youtube.com/watch?v=8Fdt5WnYn1k&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=31

Identify the conjugate acid and/or base for the following chemical Identify the conjugate acid and/or base for the following chemical. NH3 HCN C2H3O2- H2PO3- HCO3-

Instructions for making up a buffer say to mix 60mL of 0 Instructions for making up a buffer say to mix 60mL of 0.1M NH3 with 40mL of 0.1M NH4Cl. What is the pH of the buffer?

Instructions for making up a buffer say to mix 100mL of 0 Instructions for making up a buffer say to mix 100mL of 0.25M HC2H3O2 with 75mL of 0.3M NaC2H3O2. What is the pH of the buffer?

Buffers [base] pH = pKa + log [acid] pKa = -log Ka Henderson-Hasselbalch Equation Relates pH of a buffer for different concentrations of the conjugate acid-base If the molar concentration of the acid ≈ base, then the pH ≈ pKa [base] [acid] pH = pKa + log pKa = -log Ka

What must the ratio of the concentration of the HCO3- and H2CO3 buffer system found in blood be for the pH to be 7.4?

What acid-base conjugate pair could be used to make a buffer with a pH of 3.7? How would you prepare the buffer solution? H3PO4 ↔ H2PO4- + H3O+ Ka = 7.5x10-3 H2S ↔ HS- + H3O+ Ka = 1x10-7 HCO2H ↔ HCO2- + H3O+ Ka = 1.8x10-4

Calculate the pH of a buffer solution using ammonia and ammonium to which 3mL of 0.10M HNO3 is added.

Calculate the pH of a buffer solution using acetic acid/sodium acetate to which 9.5mL of 0.10M HCl is added.

Acid-Base Titrations Titration Addition of a solution of a known concentration (standard solution) to a solution of unknown concentration until the reaction is complete (reaches its equivalence point)

Acid-Base Titrations Strong Acid-Base Titrations Weak Acid-Base Titrations Strong Acid-Weak Base Titration Weak Acid-Strong Base

Calculate the pH of a solution in which 10mL of 0 Calculate the pH of a solution in which 10mL of 0.1M NaOH is added to 25.0mL of 0.1M HCl.

Calculate the pH of a solution when 25mL of 0 Calculate the pH of a solution when 25mL of 0.1M nicotinic acid (HC5H4NO2) is titrated by 20mL of 0.1M NaOH. The Ka for nicotinic acid is 1.4x10-5.

What is the pH of a solution when 35mL of 0 What is the pH of a solution when 35mL of 0.2M ammonia is titrated by28mL 0.12M HCl. The Kb for ammonia is 1.8x10-5.

What is the pH at the equivalence point when 25mL of 0 What is the pH at the equivalence point when 25mL of 0.1M HF is titrated by 0.15M NaOH?

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