Neutralization

1
Neutralization

• Pioneer High School
• Mr. Gonzalez

2
Section 21.1Neutralization Reactions

• OBJECTIVES
• Explain how acid-base titration is used to
  calculate the concentration of an acid or a base.

3
Section 21.1Neutralization Reactions

• OBJECTIVES
• Explain the concept of equivalence in
  neutralization reactions.

4
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

5
Acid-Base Reactions

• Neutralization Reaction - 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)

6
Titration

• Titration is the process of adding a known amount
  of solution of known concentration to determine
  the concentration of another solution
• Remember? - a balanced equation is a mole ratio

7
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

8
Steps - Neutralization reaction

• 1. A measured volume of acid of unknown
  concentration is added to a flask
• 2. Several drops of indicator added
• 3. A base of known concentration is slowly
  added, until the indicator changes color measure
  the volume
• Figure 21.4, page 617

9
Neutralization

• The solution of known concentration is called the
  standard solution
• added by using a buret
• Continue adding until the indicator changes color
• called the end point of the titration
• Sample Problem 21-2, page 618

10
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-

11
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

12
Equivalents

• In any neutralization reaction, the equivalents
  of acid must equal the equivalents of base
• How many equivalents of base are in 2 mol
  Ca(OH)2?
• The mass of one equivalent is its gram
  equivalent mass (will be less than or equal to
  the formula mass)
• HCl 36.5 g/mol H2SO4 49.0 g/mol

13
Equivalents

• Sample Problem 21-3, page 620
• Sample Problem 21-4, page 620

14
Normality (N)

• It is 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

15
Normality (N)

• Normality (N) equiv/L
• equiv Volume(L) x N and also know NM 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

16
Normality (N)

• Titration calculations often done more easily
  using normality instead of molarity
• In a titration, the point of neutralization is
  called the equivalence point
• the number of equivalents of acid and base are
  equal

17
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

18
Section 21.2Salts in Solution

• OBJECTIVES
• Demonstrate with equations how buffers resist
  changes in pH.

19
Section 21.2Salts in Solution

• OBJECTIVES
• Calculate the solubility product constant (Ksp)
  of a slightly soluble salt.

20
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

21
Salt Hydrolysis

• Hydrolyzing salts usually from
• strong acid weak base, or
• weak acid strong base
• Strong refers to the degree of ionization
• How do you know if its strong?
• Refer to handout provided

22
Salt Hydrolysis

• To see if the resulting salt is acidic or basic,
  check the parent acid and base that formed it
• HCl NaOH ?
• H2SO4 NH4OH ?
• CH3COOH KOH ?

23
Buffers

• Buffers are solutions in which the pH remains
  relatively constant when small amounts of acid or
  base are added
• made from a pair of chemicals a weak acid and
  one of its salts or a weak base and one of its
  salts

24
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 added, while
  the other chemical would neutralize any
  additional base
• AND, they produce each other in the process!!!

25
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

26
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

27
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

28
Solubility Product Constant

• Consider AgCl(s) ? Ag(aq) Cl-(aq)
• The equilibrium expression is
• Ag x Cl-
• AgCl

Keq
29
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

30
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

31
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

32
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
  Chateliers principle), and is called the common
  ion effect

33
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