Acids and Bases

Ionization of Water Only happens to a small amount of water

molecules H2O separates into H+ and OH-

Not the whole story H+ never occurs on its own In reality, another H2O molecule picks it up and

becomes H3O+ (hydronium ion)

Acids and Bases

Acids Bases

Taste sour Taste bitter

Feel watery Feel slippery

Conduct electricity Conduct electricity

Change litmus to red Change litmus to blue

pH = 0-7 pH = 7-14

Neutralize bases Neutralize acids

Classifying Acids and Bases Arrhenius

Acid- substance that dissociates into H+ and an anion For Example: HCl and H2SO4

Base- substance that dissociates into cation and OH-

For example: NaOH and Mg(OH)2

Does not explain bases without an OH ion

Classifying Acids and Bases (cont) Brønsted-Lowry

Acid - Proton (H+) donor For example: HCl and H2SO4

Base - Proton (H+) acceptor For example: NH3 and OH-

Conjugate Acid and Bases Occur on the other side of acid base equations. Lets look again at

NH3 is a base. It will accept a proton (H+) H2O is an acid. It will donate a proton (H+) NH4

+ is NH3’s conjugate acid. It can donate a proton (H+) to become NH3 again

OH- is water’s conjugate base. It can accept a proton (H+) to become H2O again

Amphiprotic Amphiprotic –

Substances that can act like an acid or a base Water is an amphiprotic substance.

H2O can accept a proton to become H3O+

H2O can donate a proton to become OH-

Strength of Acids and Bases Depends on how much they dissociate in

water Strong

Considered to dissociate completely in water Weak

Only partially dissociate in water Reaction is reversible ()

Conjugate pairs Strength is inversely proportional

For example: Strong acids have weak conjugate bases

Acids Strong acids

HI HBr HCl HNO3

H2SO4

HClO4

HClO3

All have 100% of the molecules break apart. There is no reverse reaction.

Weak acids All others

Polyprotic Acids Have multiple H’s H2SO4

H2SO4 gives up 1 H+ to form HSO4-

This happens to 100% of the molecules since H2SO4 is strong

HSO4- gives up another H+ to form SO4

-2

This only happens to some HSO4- because it is weak

Solution will contain A lot of water molecules H3O+ molecules (mostly from the first H+ but some from the

second and from ionization of water) HSO4

-

a little bit of SO4-2

A little bit of OH- (from the ionization of water)

Acid Names Binary acids (H with an element)

Prefix hydro- Root of element name Suffix –ic Add acid For example: HCl is hydrochloric acid

Acids with Oxygen (H with a polyatomic) Root name of polyatomic (with polyatomic prefix if applicable)

Some polyatomic roots are modified slightly to be easier to say Suffix

-ic with polyatomics ending in –ate -ous with polyatomics ending in -ite

Add acid For example: H2SO4 is sulfuric acid

Bases Strong bases

Group 1 metals with OH-

Ca, Sr, and Ba with OH-

These three are not very soluble in water, but the amount that does dissolve ionizes completely.

Weak bases All others

Chemical Equilibrium Reversible reactions Indicated with a

Both reactions are happening at the same time System reaches equilibrium when both are happening at

same rate At equilibrium

Could have lots of reactant and little product Could have lots of product and little reactant Could have equal amounts of both

Changes to the system can shift equilibrium Temperature Pressure Adding reactants or products

Equilibrium Expressions Mathematical way to represent equilibrium For the equation, aA + bB cC + dD

K = [C]c [D]d

[A]a [B]b

K is the equilibrium constant for the equation [ ] indicates the concentration of each substance

in mol/L (M) Solid and pure liquids are not entered into the

expression

Ionization of Water 2H2O(l) H3O+(aq) + OH-(aq)

This equilibrium “lies to the left” In other words, there is far more water molecules than

hydronium and hydroxide ions in a sample

Kw = [H3O+] [OH-] Kw = 1.0 x 10-14

In pure water and neutral solutions, [H3O+] and [OH-] are 1.0 x 10-7 M

In acidic solutions, [H3O+] is greater than [OH-] In basic solutions [OH-] is greater than [H3O+]

pH pH

Stands for potential of Hydrogen (really hydronium)

Logarithmic scale pH = -log [H+] or [H+] = 10-pH

Values between 0-14 with each number representing a 10-fold increase from the previous number pH 7 is acidic pH = 7 is neutral pH 7 is basic

pOH pOH = -log [OH-] or [OH-] = 10-pOH

Opposite scale pOH 7 is basic pOH = 7 is neutral pOH 7 is acidic

Indicators Compounds that change color in the presence

of different levels of pH

Soil pH 6.0-6.5

Soil pH 5.0-5.5

Neutralization (Acid-Base Reaction) Special type of double displacement reaction Acid + Base Water + Salt

Titration Process of neutralizing an acid (or base) with an

unknown concentration with a base (or acid) of a known concentration

Moles of H3O+ must equal moles of OH- for neutralization to occur

Often indicators are used to determine the end of the reaction

VaMa = VbMb

Va = volume in L of acid Ma = molarity of acid Vb = volume in L of base Mb = molarity of base