2Acid-Base Theories Essential Question: What are the properties of acids and bases, and what distinguishes the Arrhenius, Bronsted-Lowry and Lewis theories of acids and bases?
3Properties of Acids Acids taste tart or sour. Aqueous solutions of acids are electrolytes.Acids change the color of acid-base indicators.Acids react with metals to produce hydrogen gas.Acids react with bases to form water and a salt.
4Properties of Bases Bases have a bitter taste. Bases have a slippery feel.Aqueous solutions of bases are electrolytes.Bases change the color of acid-base indicators.Bases react with acids to form water and a salt.
6Arrhenius Acids and Bases Acids are hydrogen-containing compounds that ionize to produce H+ ions in aqueous solution.Bases are hydroxide-containing compounds that ionize to produce OH– ions in aqueous solution.
8Mono- Di- and Tri-protic Acids HNO3 is a monoprotic acid.H2SO4 is a diprotic acid.H3PO4 is a triprotic acid.Not all substances that contain hydrogen are acids.Not all hydrogens in acids are necessarily released as H+ ions.
15Conjugate Acids and Bases When a substance donates a hydrogen ion, what remains has the ability to accept it back.When a substance accepts a hydrogen ion, what remains has the ability to donate the ion.
16Conjugate Acids and Bases A conjugate acid is formed when a base gains a hydrogen ion.A conjugate base is remains when an acid has donated a hydrogen ion.A conjugate acid-base pair consists of two substances related by the loss or gain of H+.
17Consider Ammonia in Water NH3 + H2O NH4+ + OH–Base Acid Conjugate ConjugateAcid Base
19Hydronium ion ( H3O+ )A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion.
20Amphoteric Sometimes water accepts a hydrogen. HCl + H2O H3O+ + Cl– Other times, water donates a hydrogen.NH3 + H2O NH OH–A substance that can act as either an acid or a base is said to be amphoteric.
21Lewis Acids and BasesA Lewis acid accepts a pair of electrons during a reaction.A Lewis base donates a pair of electrons during a reaction.
22Hydrogen Ions and Acidity Essential Question:How are [H+] and [OH–] related and how do they relate to acidity?
23Hydrogen Ions from Water The reaction in which water molecules produce ions is called the self-ionization of water.H2O (l) H+ (aq) + OH– (aq)In water, H+ ions are always joined to water molecules to form H3O+ hydronium ions.
25Self-Ionization of Water This happens to a very small extent.In pure water, the concentration of H+ and OH– are equal.[H+] and [OH–] both equal 1.0 x 10-7 M.This is called a neutral solution.
26Ion Product Constant for Water In any aqueous solution, when [H+] increases, [OH–] decreases.When [H+] decreases, [OH–] increases.The product of the hydrogen-ion concentration and the hydroxide ion concentration always equals 1.0 x
27Ion Product Constant for Water Kw = [H+] x [OH–] = 1.0 x 10-14Remember, as [H+] goes up, [OH–] goes down.But the product of [H+] x [OH–] will always be 1.0 x
28Acidic vs BasicAn acidic solution is one in which the [H+] is greater than the [OH–].A basic solution is one in which the [H+] is less than the [OH–].Basic solutions are also called alkaline solutions.
32The pH ConceptExpressing hydrogen concentration in molarity can be cumbersome.A more popular method is the pH scale.The pH scale ranges from 0 to 14, with the most acidic = 0 and the most basic = 14.
33Calculating pHpH = the negative of the logarithm of the hydrogen ion concentration.pH = -log [H+]
34Calculating pOH pOH is the red-headed stepchild… pOH is the negative logarithm of the [OH–].pOH = -log [OH–]
35pH and pOHYou can calculate the pH or the pOH of a solution using the log function key on a calculator.
36pH and AcidityAcidic solution: pH < and [H+] is greater than 1 × 10−7MNeutral solution: pH = 7.0 and [H+] is equal to 1 × 10 −7MBasic solution: pH > 7.0 and [H+] is less than 1 × 10 −7M
39pH and Significant Figures Express [H+] and [OH–] in scientific notation.Express pH and pOH with the same number of digits to the right of the decimal place as the number of significant digits in the scientific notation.
55Acid Dissociation Constants Takes the same form as the equilibrium-constant expression from a balance chemical equation.For ethanoic acid, for instance, the acid dissociation constant is calculated as follows:[H3O+] x [CH3COO–]Ka =[CH3COOH] x [H2O]These are sometimes called ionization constants.
56Acid Dissociation Constants Weak acids have small Ka values.Strong acids have large Ka values.The Ka value for HCl (aq) is ∞ (infinite).Why do you think this is the case?
58Base Dissociation Constants Strong bases and weak bases refer to the degree of dissociation just like acids.For sodium hydroxide, for instance, the base dissociation constant is calculated as follows:[Na+] x [OH–]Kb =[NaOH] x [H2O]
59Neutralization Reactions Essential Question:What are the products of the reaction of an acid and a base when the endpoint of a titration is reach?
60Acid—Base ReactionsA mixture of a strong acid with an equal amount of a strong base results in a neutral solution.These reactions are called neutralization reactions.
61Neutralization Reactions Consider these examples:HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)H2SO4(aq) + 2KOH(aq) K2SO4(aq) + H2O(l)What would the net ionic equations for each of these reactions be?
62Titration Acids and bases sometimes react 1:1 HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)However, the ratio can varyH2SO4(aq) + NaOH(aq) Na2SO4(aq) + 2H2O(aq)2HCl(aq) + Ca(OH)2(aq) CaCl H2O(l)
63TitrationWhen an acid and a base are mixed, the equivalence point is when the number of moles of hydrogen ions equals the number of moles of hydroxide ions.
64TitrationYou can determine the concentration of an acid in a solution by performing a neutralization reaction.You must select an appropriate acid-base indicator.Phenolphthalein turns from colorless to pink as the pH changes from acidic to basic.
65TitrationsA measured volume of an acid solution of unknown concentration is added to a flask.Several drops of the indicator are added to the solution.Measured volumes of a base of known concentration are mixed into the acid until the indicator just barely changes color.