Transcript Acid and Bases

Acids and Bases
Max Bormes, Brittany Howse,
Joe Stein, Kathy Adamczyk
Terminology
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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.
Terminology
 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.
Types
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 Bases
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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  SO42- + H3O+
Strong Acids and Bases
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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
Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4.
Strong Bases: LiOH, NaOH, KOH, Group 1 hydroxides.
- H2SO4 molecules do not exist in water; rather, only H3O+ and HSO4- are
present.
- HBr + KOH  K+ + Br- + H20
The Generic Equations
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Generic Acid Equation:
HX(aq) + H2O(l)  H3O+(aq) + X-(aq)
Ka = [H3O+][X-]
[HX]
Generic Base Equation:
X- + H2O(l)  HX + OHKb = [HX][OH-]
[X-]
The pH Scale
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Kw = 1 x 10-14 = [H+][OH-] = Ka x Kb
pH = -log [H+]
pOH = -log [OH-] = 14 – pH
FUN 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 Acids
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Acids that contain more than 1
dissociable H+.
Example
H2SO4 is only strong for the 1st H+ ion that dissociates completely; the
2nd is a weak acid.
H2SO4 + H2O  HSO4- + H3O+
HSO4- + H2O  SO42- + H3O+
Conjucate Acid-Base Pairs
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Acid  Conjugate Base + H+
Example
HCO3- + H20  H30+ + CO32Acid
Base Conj.
Conj.
Acid
Base
 Stronger Acids form Weaker Conjugate Bases.
 Stronger Bases form Weaker Conjugate Acids.
DID YOU KNOW?
Equilibrium shifts toward the side of the reaction having the weaker acid and base.
Inductive Effect
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The inductive effect explains how acidity is increased by the
stronger attraction of electrons from adjacent bonds by a more
electronegative atom.
Example
Nitric 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.
Titrations
Let’s work one on the board shall we?
KEEP IN MIND
- 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 done
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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 End
mmmmmm…..no more acids.