AcidsAcids and and BasesBases

Max Bormes, Brittany Howse, Joe Stein, Kathy Adamczyk

TerminologyTerminology

Acid: Any substance that when dissolved in pure water, increases the concentration of H+ in the water.

[0, 7) on the pH scale. Turns litmus paper red. Turns clear in phenolphthalein.

TerminologyTerminology

Base: Any substance that when dissolved in pure water, increases the concentration of OH- in the water.

(7, 14] on the pH scale. Turns litmus paper blue. Turns pink in phenolphthalein.

TypesTypes

Acids Bases

Arrhenius produce H+ in aqueous solution

produce OH- in aqueous solution

Lewis electron acceptors in solution

electron donors in solution

Bronsted-Lowry proton donors proton acceptors

Weak Acids and Weak Acids and BasesBases

Weak Acids and Bases dissociate partially in water.

The vast majority of acids and bases are weak.

The relative strength of an acid or base can be expressed quantitatively with an equilibrium constant.

Example- NH3 + H2O NH4

+ + OH-

- HSO4- + H2O SO4

2- + H3O+

Strong Acids and Strong Acids and BasesBases

Strong Acids and Bases dissociate completely and are irreversible.

Large Ka and Kb. Ionize completely in water. Reactions between strong acids and strong

bases are called neutralizing reactions.

Example- H2SO4 molecules do not exist in water; rather, only H3O+ and HSO4

- are present.

- HBr + KOH K+ + Br- + H20

Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4.Strong Bases: LiOH, NaOH, KOH, Group 1 hydroxides.

The Generic The Generic EquationsEquations Generic Acid Equation: HX(aq) + H2O(l) H3O+

(aq) + X-(aq)

Ka = [H3O+][X-]

[HX] Generic Base Equation: X- + H2O(l) HX + OH-

Kb = [HX][OH-]

[X-]

The pH ScaleThe pH Scale

Kw = 1 x 10-14 = [H+][OH-] = Ka x Kb

pH = -log [H+] pOH = -log [OH-] = 14 – pH

FUN FUN FACT!FACT!You can find pH without a calculator!!!...sorta

If [H+] = 10-x, pH = x.Ex) for 10-8, pH = 8.

On the board: if Ka = 4.6 x 10-5 find Kb and pH.

Polyprotic Polyprotic AcidsAcids

Acids that contain more than 1 dissociable H+.

ExampleExampleH2SO4 is only strong for the 1st H+ ion that dissociates completely; the 2nd is a weak acid.

H2SO4 + H2O HSO4- + H3O+

HSO4- + H2O SO4

2- + H3O+

Conjucate Conjucate Acid-Base Acid-Base PairsPairs

Acid Conjugate Base + H+

ExampleExampleHCO3

- + H20 H30+ + CO32- Acid Base Conj. Conj.

Acid Base

Stronger Acids form Weaker Conjugate Bases. Stronger Bases form Weaker Conjugate Acids.

Equilibrium shifts toward the side of the reaction having the weaker acid and base.

DID YOU DID YOU KNOW?KNOW?

Inductive EffectInductive Effect The inductive effect explains how acidity is increased by the

stronger attraction of electrons from adjacent bonds by a more electronegative atom.

ExampleExampleNitric Acid: HNO3 and Phosphoric Acid: H3PO4

HNO3 has 2 additional oxygen atoms connected to the central atoms that increase the polarization of the molecule (Oxygen is very electronegative) and thus weakens the H-O bond. The Phosphoric Acid only has 1 Oxygen, so the H-O bond is stronger than the H-O bond in Nitric Acid, so it is less likely to dissociate completely. The more polar molecule makes it easier to dissolve in water since likes dissolve likes.

TitrationsTitrations Let’s work one on the board shall we?

KEEP IN KEEP IN MINDMIND- pH before adding base = pKa1

- At mid-point: pH = pKa

- Always check whether the solution is acting as an acid or a base at the equivilence point.

- NACAVA = NBCBVB

Buffers –almost doneBuffers –almost done A solution that resists a change in pH

when H+ or OH- ions are added. A buffer is created by adding an

excess of a weak acid and a conjugate base or a weak base and its conjugate acid.

pH = pKa + log([A-]/[HA])

The EndThe End

mmmmmm…..no more acids.