CHEM 1312H 1st Edition Lecture 2616.1 ACIDS AND BASES: A BRIEF REVIEW- acid (Arrhenius): substances that increase the concentration of H+ ions in water- base (Arrhenius): substances that increase the concentration OH- ions in water- Arrhenius definition is rather limited because it is restricted to aqueous solutions16.2 BRØNSTED-LOWRY ACIDS AND BASES- acid: a substance (molecule or ion) that donates a proton to another substanceo a substance can only function as an acid IF something else acts as a base simultaneously - base: a substance that accepts a protono a molecule or ion must have a nonbonding pair of electrons it can use to accept the H+ and bind to it- amphiprotic: a substance capable of acting as an acid or base (H2O is an ex.)o an amphiprotic substance is a base when combined with something more acidic than itself and acts as an acid when combined with something more strongly acidic than itself- conjugate acid-base pair: an acid or base such as HA and A- that differ only in the presence or absence of a protono every acid has a conjugate base (formed by removing a proton from the acid); for instance, OH- is H2O’s conjugate base and A- is HA’s conjugate baseo every base has a conjugate acid (formed by adding a proton to the base); H3O+ is H2O’s conjugate acid and HA is the conjugate acid of A-RELATIVE STRENGTH OF ACIDS AND BASES- the more easily a substance gives up a proton, the less easily its conjugate base accepts a proton- the more easily a base accepts a proton, the harder it is for the conjugate acid to give it up- the stronger an acid, the weaker its conjugate base- the stronger a base, the weaker its conjugate acid- strong acids:completely transfers its protons to water; dissociates pretty much completely- weak acids: only partially dissociates; exists in the solution as a mix of the undissociated acidand its conjugate base16.3 THE AUTOIONIZATION OF WATER: (when one water molecule donates a proton to anothermolecule; so H2O + H2O  H3O+ + OH-- no water remains ionized for very long because the forward and reverse reactions are very rapid- Kw = [H3O+][OH-] = 1.0 x 10-14These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.16.4 THE pH SCALEpH = - log[H+]pOH = - log [OH-]pH + pOH = 14.0016.6 WEAK ACIDS- most acidic substances are only partially ionized - Kais the dissociation constant; the magnitude indicates the tendency of acid to ionize in water. The larger the value, the stronger the acid. Weak acids tend to have k values ranging from 10-2 to 10-10Ka= [H3O+][A-] / [HA]- as the concentration of a weak acid increases, the equilibrium concentration of H+ (aq) increases,as expectedo however, the percent ionization decreases as concentration increases also, so doubling the concentration of a weak acid does not double the concentration of H+ (aq)POLYPROTIC ACIDS: acids that have more than one ionizable H atom- ex, H2SO3H2SO3 H+ + HSO3-Ka1 = 1.7E-2 HSO3- H+ + SO32-Ka2= 6.4E-8- Ka2 is much smaller than Ka1; because of electrostatic attractions, positively charged protons can be lost more easily from a neutral H2SO3 than a negatively charged HSO3- AKA IT’S EASIER TO REMOVE THE FIRST PROTON FROM AN ACID THAN IT IS TO REMOVE THE SECOND16.7 WEAK BASESKb = [BH+][OH-] / [B]Where Kb refers to the equilibrium in which a base reacts with water to form the corresponding conjugate acid and OH-2 Types of weak bases:1. neutral substances that have an atom with a nonbonding pair of electrons that can accept a proton: a lot of these contain a nitrogen atom; includes ammonia and amines2. anions of weak acids16.8 RELATIONSHIP BETWEEN KaAND KbFor any conjugate acid-base pair, Ka+ Kb= KwSimilarly, pKa+ pKb= pKw= 14.00 where pKa = - logKa16.9 ACID BASE PROPERTIES OF SALT SOLUTIONS- because salts are good electrolytes, any salt dissolved in water is basically completely dissociated acid base properties of salt solutions arise from cations and anions interacting with eachother- hydrolysis: when ions react with water to generate hydronium or hydroxide ions16.10 ACID-BASE BEHAVIOR AND CHEMICAL STRUCTURETRENDS:- a molecule with H will act as a proton donor only if the H—A bond is polarized so that the Hatom has a partial positive chargeo nonpolar H—A bonds like H—C in CH4 produce neutral aq solutionso if the bond is polarized like it is in NaH when the H has a negative charge and behaveslike a proton acceptor, it’s basico bond strength also plays a role; bond strength increases as you move up the HI HBrHClHF groupo lastly, the more stable the conjugate base is, the stronger the acid- for BINARY ACIDS in which A represents members of the same group in the periodic table:o H—A bond strength decreases as element A increases in size aka down a period, bondstrength  (decreases) and acidity  (increases)o acidity increases as the electronegativity of A increases (so increases as you move left toright across a period)o for more trends, see table below (from pg. 706 of Chemistry, the Central Science (13thedition, Brown LeMayBursten Murphy Woodward Stoltzfus)- for OXYACIDS in which OH groups and possibly additional oxygen atoms are bound to a centralatom - the strength of an acid increases as additional electronegative atoms bond to thecentral atom- for CARBOXYLIC ACIDS that are often written as COOH (benzoic acid, formic acid, etc.)o the additional oxygen atom attached to the carbon of the carboxyl group draws electrondensity from the O—H bond this increases its polarity also helps stabilize the conjugate base16.11 LEWIS ACIDS AND BASESRecall: a Lewis acid is an electron-pair acceptor, and a Lewis base is an electron-pair