2 Objectives State the Bronsted-Lowry definition of acids and bases Identify the common physical and chemical properties of acids and basesExplain what dissociation constants indicate about an acid or baseUse experimental data to calculate a dissociation constant
3 Properties of acids/bases Taste – acid comes from latin meaning sour or tart/bases are bitter – soapTouch most dilute acids feel like water although they sting on broken skin bases feel smooth, soothing and slippery except in your eyes (soap)Reactions with metal acids react bases do not react
4 Properties continuedElectrical conductivity water is poor – HCl is good, NaOH is good both are electrolytesIndicators turn color – acid turns litmus paper from blue to red base turns from red to blueNeutralization reaction between an acid and a base get salt and water (double replacement)
5 Arrhenius definitionAn acid is a substance that dissociates in water to produce hydrogen ions.A base is a substance that dissociates in water to produce hydroxide ionsA salt is an ionic compound formed from any cation other that H+ and any anion other than OH- or O-2
6 Arrhenius continued Acids react with metals to produce H2 gas Mg +2H+ -> Mg+2 + H2oxidation reduction reaction
7 Bronsted – Lowry definitions An acid is any substance that can donate H+ ionsA base is any substance that can accept H+ ions a Bronsted-Lowry acid is a proton donor and a base is a proton acceptor
8 Hydronium IonH+ is strongly attracted to the electrons of surrounding water moleculesH+ + H2O -> H3O+More correct HCl + H2O -> H3O++ Cl-In this case HCl is the Bronsted-Lowry acid and water is the baseWe still describe a solution of HCl as acidic!
9 Amphoteric a substance that can act as either an acid or a base NH3 + H2O -> NH4+ + OH- Ammonia is the H+ acceptor water is the H+ donor (acid)Amphoteric a substance that can act as either an acid or a base
10 Conjugate Acid-Base Pairs NH3 + H2O NH4+ + OH-In 1 direction water is the acid in the reverse reaction it is the base.These cmpds become conjugate acids and conjugate bases when HCl loses an H+ ion to become its conjugate base Cl- when the conjugate base of water is the hydroxide ion OH-When ammonia gains H+ to become its conjugate acid NH4+ and the conjugate acid of OH- is H2O
11 Conjugate pairsA pair of compounds that differ by only one H+ ion such as H2O and OH- or NH3 and NH4+ are called conjugate acid base pairsNH3 + H2O NH OH-Base acid conj. Acid conj. base
12 Determining the strengths of acids and bases A strong acid HCl readily transfers hydrogen ions to water to form H3O+If you place 1M of HCl in 1 liter of water you would form 1 M H3O+ ions and 1 M Cl- ions
13 weak acids A weak acid does not readily transfer H+ ions 1 mole of acetic acid in 1 liter of water only .4% of the acetic acid molecules would form H3O+ and C2H3O2-. Which means that 99.6% of the acetic acid molecules do not dissociate.
14 To show a strong acid from a weak acid use arrows HCl + H2O H3O+ + Cl-HC2H3O2 + H2O <-> H3O+ + C2H3O2-
15 Strong and Weak BasesThe most widely used commercial base is CaO. When CaO is dissolved in water the O-2 ions react completely with H2O to form OH- ions.O-2 + H2O 2OH- use a single arrow
16 Strength of conjugate acid – base pairs The stronger the acid the weaker its conjugate base.The stronger the base the weaker its conjugate acid.
17 The acid dissociation constant Ka Weak acid HAHA + H2O <--> H3O+ + A-Keq =For a 1 M solution of a typical weak acid may be only .007% of the water molecules react. Move the water to the left side of the equationThe higher the Ka the more the reaction goes to the right . The greater the Ka the stronger the acidWeak acids have a Ka less than 1
19 Base dissociation constant Kb The base dissociation constant is a measure of the strength of a baseDo calculations of dissociation constants
20 Objectives Explain what most acidic hydrogen atoms have in common Explain what most bases have in commonDescribe how acids are named
21 Naming and identifying acids and bases 1st all H’s are not acidic CH4As a rule an acidic hydrogen already has a slight positive charge while is it part of a molecule. (It is in the positive side of a polar covalent bond)Usually bonded with O, N, or a halogen
22 3 types of acids Binary acids - H and 1 other element usually 6A or 7A Strong HCl, HBr, and HIWeak HF, H2S and H2SeOxy acids contain H, O and 1 other elementH2SO4, HNO3 and H3PO4Carboxylic Acid – organic acids COOH groupAcetic acid HC2H3O2 vinegar
23 BasesA Bronsted-Lowry base always contains an unshared pair of electrons NH3 attracts H+Anions: remember conjugate bases HCl Cl-Weak Cl- Br- I- NO3- HSO4- CIO4-Strong O-2 OH- PO4-3 and CO3-2Amines N has an unshared pr. Of electrons
24 Naming Acids and BasesIf the name of an anion ends in ide the name of the acid that produces it includes the name of the anion, a hydo prefixHydrochloric acid – all binary acidsIf the name of an anion ends in ate use and ic ending Nitric acid, carboxylic acidAnion ends in ite SO3-2 sulfite ion H2SO3 sulfurous acid