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BACK                                                    Bases, Acids, and Salts

I   Defining Acids and Bases
A.  properties of acids and bases
1.  taste
a. acids - sour or tart
b. bases - bitter
c.  never taste chemicals in a lab 
2.  touch
a. acids
1.  dilute feel like water on normal skin
2.  injured skin will sting
b.  bases
1.  mild do not sting

  1. smooth, soothing, and slippery

3.  reaction with metals

a.  acids
1.  react vigorously
2.  produce hydrogen gas
b.  bases do not
4.  electrical conductivity
a.  acid and bases conduct electricity well
b.  both ionize in water
c. pure water poor conductor
5.  indicators
a.  acid-base - turn one color in an acid and another color in a base
b.  litmus common indicator - comes from lichens
c.  litmus test
1.  acids turn litmus from blue to red
2.  bases turn litmus from red to blue
d.  others
1.  phenolphthalein
2.  methyl red
  1. thymol blue

6.  neutralization
a.  mix an acid with a base
b.  acid eliminates the basic properties
c.   base eliminates the acidic properties
d.  called a neutralization reaction
e.  forms a ionic compound - salt
1.  crystalline compound
2.  high melting
3.  many ionize and dissolve in water
  1. conduct electricity
B.  the Arrhenius definition
1.  can use properties to identify acids and base
2.  chemists studied structure and composition to identify acids and bases
3.  Arrhenius - 1884
a.  acids in water produce hydrogen ions  (H+)
ex.  HCl, HNO3, H2SO4
b.  bases in water produce hydroxide ions (OH-)
ex.  NaOH, KOH, Mg(OH)2
4. neutralization reactions always produce water and a salt
5.  explains properties of acids and bases
:
a.  electrolytes - form ions (H+ and OH-)
b.  acids sour taste - H+
c.  bases slippery - OH-
d. salts definition - made from cation other than H+ and  anion other than OH-
6.  definition limitations
a.  restricts acids and bases to water solutions
b.  does not explain H+ formation  (H3O+ hydronium ion)
  1. does include bases that do not contain OH-  ex. NH3
C.  the Brønsted-Lowry definition
1.  independently proposed:
a.  acid donate H+
b.  bases accept H+ 
2.  H+ is simply a proton
3.  acid is a proton donor
a.  HCl - nonprotic acid
b.  H2SO4 - diprotic acid
c.  H3PO4 - triprotic acid
  1. base is a proton acceptor

D.  the hydronium ion
1.  acids don't simply dissociate into H+
2.  acids transfer H+ to water
a.  HCl + H2O ---> H3O+ Cl-
b.  H3O+  gives water solutions acidic properties
3.  NH3 + H2O ---> NH4+ + OH-   
a.  H2O is proton donor
b.  B-L acid
c.  OH- gives water solution basic properties
4.  water is amphoteric - can be both an acid and a base depending
on the circumstances

E.  conjugate acid-base pairs  (joined together)
1.  NH3 + H2O === NH4+ + OH-  reversible reaction
2.  NH3 - base   forward reaction H2O - acid
3.  NH4+ - acid   reverse reaction OH- - base
4.  difference in an acid and a base can be one H+
5.  conjugate acid-base pairs
a.  base gains H+ becomes a conjugate acid 
ex.  NH3 (base)  ---> NH4+ (conjugate acid)
b.  acid loses H+  becomes a conjugate base
ex.  H2O (acid)  ---> OH-  (conjugate base)


II.  Determining the strengths of Acids and Bases
A.  strong and weak acids
1.  strong
a.  nearly 100% dissociation of the acid
b.  acids that react completely to form ions
c.  strong electrolytes
1.  1M HCl + H2O ---> 1M H+ + 1M Cl-
2.  single arrow used in the reaction
d.  strong acids
1.  hydrochloric
2.  hydrobromic
3.  nitric
  1. Sulfuric

2.  weak

a.  little dissociation
b.  acids that do not completely form ions
c.  poor electrolytes
1.  1M HC2H3O2 + H2O   === .004M H+ + .004M C2H3O2-                                   
2.  two half arrows used
d.  99.6% of HC2H3O2 remains un-ionized
e.  weak acids
1.  acetic
2.  hydrocyanic
3.  hydrofluoric
  1. Nitrous

B.  strong and weak bases
1.  strong
a.  strongest affinity for H+
b.  OH- strong base
c.  strong
1.  NaOH
2.  KOH
3.  CaO
d.  CaO
1.  lime widely used
2.  O2- strong attraction for H+
  1. O2 +  H2O ---> 2 OH-

2.  weak
a.  partially reacts with water to form OH-
b.  most common
1.  NH3
2.  CO32-
3.  PO43-
  1. CO32- + H2O  === HCO3- + OH-
C.  strength of conjugate acid-base pairs
1.  inverse relationship
2.  strong acid - weak conjugate base
  1. strong base - weak conjugate acid

D.  the acid dissociation constant (Ka)
1.  Keq of weak acids multiplied times [H2O] to get the Ka
2.  Keq  = [H3O+] [A-] ---->Keq  [H2O] = [H3O+] [A-] ---->  Ka = [H3O+] [A-]
                 [HA] [H2O]                                    [HA]                             [HA]
3.  K
a  is a measure of the strength of acids
4.  weak acid - K
a < 1
5.  diprotic and triprotic acid each dissociation step has its own K
a
  1. each successive Ka smaller than the previous step

E.  the base dissociation constant  (Kb
1.  measure the strength of a base
2.  K
eq of weak base multiplied times [H2O] to get the Kb
3.  Kb = [HB+] [OH-]
                      [B]

F.  acid-base of salt
1.  strong electrolyte
2.  salts ions react with water - salt hydrolysis reaction
3.  will produce an acid(H3O+)  or base(OH-) solution
4.  predicting
a.  salts of strong acids and bases -> neutral
b.  salts of strong acids-weak bases -> acidic
c.  salts of weak acids-strong bases -> basic
d.  salts of weak acids-weak bases -> acidic, basic, or neutral


III.  Naming and Identifying Acids and Bases
A.  acids
1.  donate an H+
2.  H+ called an acidic hydrogen
3.  acidic hydrogen has slight + charge
4.  H bonded to oxygen, nitrogen, or halogens
5.  three categories
a.  binary
1.  hydrogen and one other element
2.  other element usually 6A or 7A groups
             
     
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