# Chapter 21 - Neutralization

W
Shared by:
Categories
Tags
-
Stats
views:
33
posted:
5/25/2012
language:
pages:
33
Document Sample

```							  Chapter 21
“Neutralization”
Section 21.1
Neutralization Reactions
 OBJECTIVES:

–Explain how acid-base
titration is used to calculate
the concentration of an acid or
a base.
Section 21.1
Neutralization Reactions
 OBJECTIVES:

–Explain the concept of
equivalence in neutralization
reactions.
Acid-Base Reactions
 Acid + Base  Water + Salt
 Properties related to every day:
–antacids depend on neutralization
–farmers use it to control soil pH
–formation of cave stalactites
–human body kidney stones from
insoluble salts
Acid-Base Reactions
 NeutralizationReaction - a reaction
in which an acid and a base react in
an aqueous solution to produce a
salt and water:
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
H2SO4(aq) + 2KOH(aq)  K2SO4(aq) + 2 H2O(l)
– Table 21.1, page 614 lists some salts
Titration
 Titration
a known amount of solution of
known concentration to
determine the concentration of
another solution
 Remember? - a balanced
equation is a mole ratio
 Sample Problem 21-1, page 616
Titration
 The concentration of acid (or base)
in solution can be determined by
performing a neutralization reaction
–An indicator is used to show
when neutralization has occurred
–Often use phenolphthalein-
colorless in neutral and acid;
turns pink in base
Steps - Neutralization reaction
#1. A measured volume of acid of
#2. Several drops of indicator added
#3. A base of known concentration is
changes color; measure the volume
 Figure 21.4, page 617
Neutralization
 Thesolution of known
concentration is called the
standard solution
– added by using a buret
 Continue
changes color
– called the “end point” of the titration
 Sample   Problem 21-2, page 618
Equivalents
 One mole of hydrogen ions reacts
with one mole of hydroxide ions
– does not mean that 1 mol of any acid
will neutralize 1 mol of any base
– because some acids and bases can
produce more than 1 mole of
hydrogen or hydroxide ions
– example: H2SO4(aq)  2H+ + SO42-
Equivalents
 Made   simpler by the existence of a
unit called an equivalent
 One equivalent (equiv) is the
amount of acid (or base) that will
give 1 mol of hydrogen (or
hydroxide) ions
– 1 mol HCl = 1 equiv HCl
– 1 mol H2SO4 = 2 equiv H2SO4
Equivalents
any neutralization reaction, the
 In
equivalents of acid must equal the
equivalents of base
– How many equivalents of base are in
2 mol Ca(OH)2?
 Themass of one equivalent is it’s
gram equivalent mass (will be less
than or equal to the formula mass):
HCl = 36.5 g/mol; H2SO4 = 49.0 g/mol
Equivalents
 Sample Problem 21-3, page 620
 Sample Problem 21-4, page 620
Normality (N)
 Itis useful for us to know the
Molarity of acids and bases
 Often more useful to know how
many equivalents of acid or base a
solution contains
 Normality (N) of a solution is the
concentration expressed as
number of equivalents per Liter
Normality (N)
 Normality  (N) = equiv/L
 equiv = Volume(L) x N; and also
know: N=M x eq; M = N / eq
 Sample Problem 21-5, page 621
 Diluting solutions of known Normality:
N1 x V1 = N2 x V2
 N1 and V1 are initial solutions
 N2 and V2 are final solutions
Normality (N)
 Titration  calculations often done
of molarity
 In a titration, the point of
neutralization is called the
equivalence point
– the number of equivalents of acid and
base are equal
Normality (N)
 Doing titrations with normality use:
NA x VA = NB x VB
 Sample Problem 21-6, page 623
 Sample Problem 21-7, page 623
 Sample Problem 21-8, page 624
Section 21.2
Salts in Solution
 OBJECTIVES:
–Demonstrate with equations
how buffers resist changes in
pH.
Section 21.2
Salts in Solution
 OBJECTIVES:

–Calculate the solubility
product constant (Ksp) of a
slightly soluble salt.
Salt Hydrolysis
A  salt is an ionic compound that:
–comes from the anion of an acid
–comes from the cation of a base
–is formed from a neutralization
reaction
–some neutral; others acidic or basic
 “Salt hydrolysis” - a salt that reacts
with water to produce acid or base
Salt Hydrolysis
    Hydrolyzing salts usually from:
1. strong acid + weak base, or
2. weak acid + strong base
    Strong refers to the degree of
ionization
    How do you know if it’s strong?
– Refer to handout provided
Salt Hydrolysis
 Tosee if the resulting salt is
acidic or basic, check the
“parent” acid and base that
formed it:
HCl + NaOH 
H2SO4 + NH4OH 
CH3COOH + KOH 
Buffers
 Buffers are solutions in which the
pH remains relatively constant
when small amounts of acid or
–made from a pair of chemicals:
a weak acid and one of it’s
salts; or a weak base and one
of it’s salts
Buffers
A  buffer system is better able to
resist changes in pH than pure water
 Since it is a pair of chemicals:
–one chemical neutralizes any acid
base
–AND, they produce each other in
the process!!!
Buffers
 Example:   Ethanoic (acetic) acid
and sodium ethanoate (also called
sodium acetate)
 Examples on page 628 of these
 The buffer capacity is the amount
of acid or base that can be added
before a significant change in pH
Buffers
 Buffers that are crucial to maintain the
pH of human blood:
1. carbonic acid (H2CO3) & hydrogen
carbonate (HCO31-)
2. dihydrogen phosphate (H2PO41-) &
monohydrogen phoshate (HPO42-)
 Table 21.2, page 629 has some
important buffer systems
 Sample Problem 21-9, page 630
Solubility Product Constant
 Salts differ in their solubilities
–Table 21.3, page 631
 Most “insoluble” salts will
actually dissolve to some
extent in water
–said to be slightly, or
sparingly, soluble in water
Solubility Product Constant
 Consider: AgCl(s)  Ag+(aq) + Cl-(aq)
 The “equilibrium expression” is:

[ Ag+ ] x [ Cl- ]
Keq =
[ AgCl ]
Solubility Product Constant
 But, the [ AgCl ] is constant as long
as some undissolved solid is
present
 Thus, a new constant is developed,
and is called the “solubility product
constant” (Ksp):
Keq x [ AgCl ] = [ Ag+ ] x [ Cl- ] = Ksp
Solubility Product Constant
 Values  of solubility product
constants are given for some
common slightly soluble salts in
Table 21.4, page 632
 Although most compounds of Ba are
toxic, BaSO4 is so insoluble that it is
used in gastrointestinal
examinations by doctors! - p.632
Solubility Product Constant

 To  solve problems: a) write
equation, b) write expression, and
c) fill in values
 Sample Problem 21-10, page 634
 Sample Problem 21-11, page 634
Common Ion Effect
   A “common ion” is an ion that is
common to both salts in solution
– example: You have a solution of lead
(II) chromate. You now add some
lead (II) nitrate to the solution.
• The lead is a common ion
– This causes a shift in equilibrium (due
to Le Chatelier’s principle), and is
called the common ion effect
Common Ion Effect
 Sample   Problem 21-12, page 636
 The solubility product constant (Ksp)
can be used to predict whether a
precipitate will form or not:
– if the ion-product concentration is
greater than the allowed Ksp, then a
precipitate will form
 Sample   Problem 21-13, page 637

```
Related docs
Other docs by Lwjp86