Acid-Base Properties and Theories

Chemistry 12/12AP

Properties of Acids• Sour taste• Turn blue litmus red (and other indicators)• Neutralize bases• Conduct electricity (electrolytes)• React with active metals (group I, II) to produce H2 gas

• React with metal oxides to produce a salt of the metal and water

• Produce H+ or H3O+ in solution (see acid-base theories)

• pH less than 7

Properties of Bases

• Bitter taste ex. tonic water (quinine)• Turn red litmus blue (and other indicators)• Neutralize acids• Conduct electricity (electrolytes)• Feel slippery (soapy)• pH greater than 7• Produce OH- in solution

Arrhenius Theory

An Acid is a substance that produces H+ ions in solution.

A base is a substance that produces OH- ions in solution.

Neutralization occurs when H+ ions combine with OH- ions to form water.

)()()(: 2 lOHaqOHaqHequationionicNet

)()()()( 2 aqNaCllOHaqNaOHaqHCl

)()()()( 2 aqNaCllOHaqNaOHaqHCl

Acid or Base (Arrhenius Style)

• H2SO4

• Ca(OH)2

• Pb(NO3)2

• NaHCO3

• NaOH• HBr

Limitations of Arrhenius Theory

• Acids (like HCl) are able to be neutralized by NaOH and NH3.

• Not all bases have OH- ions, NH3 in H2O does, but, if NH3 reacts as a gas with HCl gas, NH4Cl is still formed, but is not a solution, so this theory won’t always work.

)()()(

)()()()(

43

2

aqClNHaqHClaqNH

lOHaqNaClaqNaOHaqHCl

Bronsted-Lowry Theory

• An acid is a proton donor.• A base is a proton acceptor.

ClOHHClOH 32

H3O+ is a hydronium ion (aka. THE

PROTON)

HCl is the acid

H2O is the base.

Writing Conjugates

• See Board notes

Conjugate Acid-Base Pairs

A conjugate acid is the substance that hasaccepted the proton (gained an H+)A conjugate base is the substance that has lostthe proton.Each acid has a conjugate base and each basehas a conjugate acid.

Formation of Acids

• Acids are formed when a non-metal oxide is dissolved in water (forms an oxyacid)

SO2 + H2O H2SO3

Acid Nomenclature

Formation of Bases

• Formed when a metal oxide reacts with water (forms a strong base)

Na2O + H2O 2NaOH

Relative Strengths of Acids and Bases

Strong Acids & Bases

• Strong acids – hydrogen halides, oxyacids of halogens, sulfuric acid & nitric acid

• Strong bases – NaOH, KOH, Cs(OH)2, Ca(OH)2

• Both of these ionize completely in H2O.

OHNaNaOH

ClOHOHHCl 32

Weak Acids & Bases

• Weak acids and bases do not ionize completely in water

• A weak acid/base will be shown with a double arrow reaction, and also have small Ka and Kb values

Self-ionization of Water

Ionization Constants

Acid ionization constant (Ka)• Magnitude dictates the

strength of the acid• Strong acids have large Ka

values – this means that they dissociate completely (100%)

• Weak acids have small Ka values – and do not dissociate completely (usually 5% or so)

Base ionization constant (Kb)• Magnitude dictates the

strength of the base• Strong bases have large Kb

values – and dissociate completely (100%)

• Weak bases have small Kb values - and do not dissociate completely (5% or so)

Ion Product of Water (Kw)

Kw = 1.0 x 10-14=[H+][OH-] – changes with temperature

Kw = Ka x Kb- Uses: Can find concentration of OH- or H+, the

Kb of the conjugate base (and vice versa), or used with pH or pOH calculations when necessary

pH and pOH

pH = -log10[H+] or pH = -log10[H3O+] (same thing)

[H+] = 10-pH

pOH = -log10[OH-]

[OH-] = 10-pOH

pH Scales

Ionization Constants of Weak Acids & Bases

Equilibrium Problems Using Acids

Type 1: Solving for KaYou must have the following:

- the equation for the reaction- the equilibrium expression- the concentrations at equilibrium (ICE chart)

- The concentrations at equilibrium are usually found with pH or a % ionization.

Equilibrium Problems Using Acids

Type 2. Solving for EQ amounts You must have the following:

- the reaction- the equilibrium expression and Ka value- the initial concentration of the acid (in mol/L)

- With this type, it may ask for the pH at equilibrium