Chapter 13: Acids & Bases

amphorteric

- any compound that can act as both an acid and a base in solution

strong base

-A base that dissociates completely into ions in solution. -hydroxides of groups 1 & 2 elements are strong bases

bronsted-lowry definition

-Acid: act as proton (H+) donors -Base: act as proton (H+) acceptors

Arrhenius definition

-Acids produce H+ in solution -Bases produce OH- in solution

strong vs weak acids and bases

-Strong acids and bases fully dissociate when placed in water. These substances have very large equilibrium constants which means that the equilibrium would lie very much to the right and favor the products. -Weak acids and bases only partly dissociate when placed in water. They have small equilibrium constants.

weak bases

-Substances capable of accepting hydrogen but do not completely ionize in solution -methylamine, dimethylamanine, trimethylamine, ethylamine, pyridine

Ka/ Kb magnitude

-The higher Ka is, the more easily the acid dissociates, and the stronger it is (easier to pull off a proton) -The higher Kb is, the more easily the base dissociates, and the stronger it is (creates more OH- )

conjugate base

-a base that forms when an acid loses a proton

in basic solutions...

-concentration of H+ < concentration of OH- -pH > 7

in acidic solutions...

-concentration of H+ > concentration of OH- -pH < 7

conjugate acid-base pair

-consists of two substances related to each other by the donating and accepting of a hydrogen ion

in neutral solutions...

-equal H+ and OH- concentrations -pH of 7

pOH

-log[OH-]

lewis exceptions

-molecules can't be a lewis acid if they have a full octet unless the are an exception to the octet rule (like P or S) -- can only act as a lewis base if it has a full octet -if a molecule has no lone pairs it can act as a lewis acid

pH scale

-represents a solution's acidity pH= -log[H+]

salts producing neutral solutions

-salts consisting of cations of strong bases and anions of strong acids will yield neutral solutions

conjugate acid

-the particle formed when a base gains a hydrogen ion

acid dissociation constant

-the ratio of the concentration of the dissociated form of an acid to the undissociated form -if Ka >1 : high product concentration, forward rxn -if Ka < 1: low concentration of products, reverse reaction

Water (amphoteric)

-water can act as a base or an acid

Acid-Base Properties of Salts

-when a salt is dissolved in water, it breaks up into its ions, which move about independently in dilute solutions- under certain conditions these ions behave as acids or bases

autoionization of water

-when pure water reacts with itself to for hydronium and hydroxide ions

salts producing acidic solutions

1. salts containing cations of weak bases will yield acidic solutions 2. salts containing highly charged metal ions yield acidic solutions; due to interactions with the water molecule, the highly charged metal ion will cause one of the protons of water to come off which decreases the pH ex: FeCl3

Kw

1.0 x 10^-14 14 = pH + pOH

models for acids and bases

H2O: is all except a lewis acid because it already has an octet of electrons

weak acids examples

H3PO4 HNO2 HC2H3O2 HOCL HCN HF NH4+

strong acids examples

HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3

dissociation constant for water

In all aqueous solutions, Kw= 1 x 10 ^-14 (at 25C)

predicting the pH of salt solutions

Ka > Kb = acidic (pH below 7) Kb > Ka = basic (pH above 7) Ka = Kb neutral pH of 7

acid strength

The strength of an acid is defined by the equilibrium position of its dissociation (ionization) reaction - strong acid has an equilibrium that lies far to the right; -strong acids yield weak conjugate bases -weak acids: equilibrium lies far to the left -weak acids yield strong conjugate bases

polyprotic acid

acids that can donate more than one H+ to solutions

5% rule

for weak acids and bases, the equilibrium concentration is equal to the initial concentration (as long as percent dissociation is less than 5%)

lewis acids and bases

lewis acid: electron pair acceptor lewis base: electron pair donor -the lewis model covers many reactions involving substances not classified as acids or bases in other models

salts producing basic solutions

salts containing anions of weak acids (and cations of strong bases) will yield basic solutions

percent dissociation

the ratio of the amount of a substance that is dissociated at equilibrium to the initial concentration of the substance in a solution, multiplied by 100