Chemistry SM-1232
Week 8 Lesson 1
Dr. Jesse Reich
Assistant Professor of Chemistry
Massachusetts Maritime Academy
Spring 2008
Class Today
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Hand Back Work
Grades Updated
Quick Reflection
Class on Friday
Turn in the quiz today if you haven’t
Today Chapter 14: Acids and Bases
Chapter 14 Quiz Monday!
Chapter 13 and 14 Test Wednesday.
Wiki Project next month!
Learning is a frustrating
process
• Easily learnt things are easily forgotten
• Real learning takes time, effort, frustration
• Real learning makes you master subjects
Arrhenius acid
• HCl  H+ + Cl• H2SO4  2H+ + SO42• H3PO4  3H+ + PO43-
Hydronium ion
• H+ when in water reacts with water to make
an hydronium ion
• H+ + H2O  H3O+
Arrhenius Base
• A compound that produces OH- ions when
dissolved in water.
• NaOH  Na+ + OH• Mg(OH)2  Mg2+ + 2OH-
Typical Bases
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NaOH, sodium hydroxide
KOH, potassium hydroxide
NaOCH3, Soidum methoxide
Calcium Carbonate
Bronsted-Lowry
Definition
• This definition rests on the transfer of H+ ions.
• Bronsted acid is a proton H+ donor
• Bronsted base is a proton H+ acceptor
Acid Example
• HCl + H2O  H3O + Cl• H2SO4 +2 H2O  2H3O+ + SO42-
Amphoteric
• Water is amphoteric because it can act like an
acid or base.
• HCl + H2O  H3O+ +Cl• NH3 + H2O NH4+ OH-
Conjugate Acid-Base
Pairs
• NH3 + H2O  NH4+ + OH• Base, acid  conjugate acid, conjugate base
• On the left NH3 gained it’s a base
• H2O gave H+ it’s a base
• On the right, now NH4+ has an H+ to give so
it’s the conjugate acid
• OH- lost the H+ so now it’s the conjugate base
Acid Base Reactions
• Neutralization
• Acid Reactions
• Base Reactions
Neutralization
• Most common reaction!
• For Arrhenius acid Base Reactions:
• Acid + Base = Water + Salt
• For Bronstead acid base reactions:
• AcidH+ + Base-  conjugate base- + conjugate acid+
Titrations
• Use the reaction formula to determine the
molar ratio of acid to base.
• Use a known amount of acid (or base) and an
unknown amount of base (or acid).
• Drop in color changing indicator
• Add base to acid with indicator until the
solution changes color. At that point more
base is present than acid.
Titrations
• You have 30mL of a 3M solution of NaOH. You
perform three titrations using 3M solutions of
HCl, H2SO4, and H3PO4. Write three
balanced equations. How many mL of each
acid solution will it take to make the indicator
change color.
Concentration
• Another term for molarity is concentration.
• You’ve used this before with oranje juice from
concentrate. It’s comes in a concentrated
form and then you have to dilute it down.
• Concentration is written by putting a molecule
in brackets like this [HCl], which would mean
the concentration of HCl.
• A solution that is 1.0M in HCl can be written
like [HCl] = 1.0M
Strong Acids
• Strong acids fully dissociate in water. That
means water tears every molecule of the acid
into H+ ions and base – ions.
• HCl  H+ + Cl-
• Good electrolyte, meaning strong acid
solutions conduct electricity since so many
charges are in solution.
Mono or multiprotic
• Some acids only release 1 proton (H+ ion).
Others release more than one.
• HCl is monoprotic
• Sulfuric acid H2SO4 is diprotic
• Phosphoric acid H3PO4 is triprotic
Weak Acids
• Weak acids do not completely ionize
• HF is a weak acid
• In solution it become H+ and F- when it ionizes, but
there are strong electrostatic attractions F- and H+ so
they come back together.
• HF + H2O  H3O+ + F• As a consequence weak acids are poor electrolytes
and electricity is not conducted through their
solutions well.
Tug of War
• The solvent pulls the charges apart and
dissolves them, but the oppositely charged
particles are attracted to each other.
• Generically speaking
• HA + H2O  H3O + A• If the acid is strong the products are favored
and the reactants are barely present. If the
acid is weak the reactants are favored and the
products are barely present.
Rule of thumb
• HA + H2O  H3O + A• HA is the acid
• A- is the conjugate base
• The stronger the acid the weaker the
conjugate base.
Strong Bases
• A strong base completely dissociates in
solution into the ions that make it up.
• NaOH  Na+ + OH• A 1M solution of NaOH will have [Na+]= 1M
and [OH-]=1M.
• Strong bases make good electrolytes.
• For the purpose of this class any hydroxide is a
strong base.
Weak Bases
• Weak bases do not fully dissociate in water.
Most weak bases do not have a hydroxide ion
as part of them.
• In order to act in a basic manner the weak
base reacts with water to steal a proton, and
that interaction creates the OH- ion.
• NH3 + H2O  NH4+ + OH-
Weak Bases
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Generically speaking
B + H2O  BH+ + OHB= base
BH+= conjugate acid
• The stronger the base the weaker the
conjugate acid.
• The book has a list of common weak bases on
page 505
Time to hurt you!
• Water is amophoteric. It can act like a base or
an acid.
• HCl + H2O  H3O + Cl• NH3 + H2O  NH4+ + OH• Water can act like it’s own acid and base
• H2O + H2O  H3O+ + OH-
Water’s Ion Product
Constant
• H2O + H2O  H3O+ + OH• Scientists have measured how much this
happens at 25C in pure water.
• The concentration (aka molarity) of each ion is
1.0e-7M. Aka [H3O+]=[OH-]=1.0e-7
• If you multiply the concentration of
[H3O]X[OH-] you get 1.0e-14.
• This is considered the ion product constant for
water (Kw).
Kw
• Kw= [H3O+]X[OH-]
• Kw= 1.0e-7 X 1.0e-7
• Kw= 1.0e-14
Quick Math Break
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Answer the following
1.0e6 X 1.0e7=
1.0e 6 / 1.0e12=
1.0e6 X 4.5=
1.0e6 / 3.2=
4.2e-13/ 3.3 e-4 =
How does this help us?
• It becomes a 3 variable problem!
• Kw=[H3O+] X [OH-]
• We know Kw and if we know H3O or OH- we
can solve for the other one!
• Work this one out. If [H3O+]=1e-3 then what
must the [OH-] be equal to?
Solution
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Kw=[H3O+] X [OH-]
Kw/[H3O+] = [OH-]
1e-14/1e-3 = [OH-]
1e-11 = [OH-]
Acidic or basic?
• In the previous example you found that the
acid concentration was 1e-3 and the base
concentration was 1e-11.
• Is there more acid or base in solution? So, is
the solution acidic or basic?
• It’s acidic! If you don’t see why write out the
number 1e-3 and write out the number 1e-11.
Handy Reference
• In acidic solutions [H3O+] > [OH-]
• In neutral solutions [H3O+] = [OH-]
• In basic solutions [OH-] > [H3O+]
Work
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Read 509 through the end of the chapter.
Copy over the example problems
Chapter 14 HW due Monday.
Quiz on Chapter 14 Monday.
Test on Chapter 13 and 14 Wednesday April
29th. We will have class May 1st to start
chapter 15.