Acid and Base Equilibrium - PowerPoint PPT Presentation

Loading...

PPT – Acid and Base Equilibrium PowerPoint presentation | free to download - id: 71131a-MGJiN



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Acid and Base Equilibrium

Description:

Acid and Base Equilibrium – PowerPoint PPT presentation

Number of Views:16
Avg rating:3.0/5.0
Slides: 47
Provided by: J945
Learn more at: http://www.manningsscience.com
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Acid and Base Equilibrium


1
Acid and BaseEquilibrium
2
Some Properties of Acids
  • Produce H3O ions in water (the hydronium ion
    is a hydrogen ion attached to a water molecule)
  • Taste sour
  • Corrode metals
  • Electrolytes
  • React with bases to form a salt and water
  • pH is less than 7
  • Turns blue litmus paper to red

3
Some Properties of Bases
  • Produce OH- ions in water
  • Taste bitter, chalky
  • Are electrolytes
  • Feel soapy, slippery
  • React with acids to form salts and water
  • pH greater than 7
  • Turns red litmus paper to blue Basic Blue

4
Acid/Base definitions Definition 1 Arrhenius
Arrhenius acid is a substance that produces
(H3O) in water
Arrhenius base is a substance that produces OH-
in water
5
Acid/Base Definitions
  • Definition 2 Brønsted Lowry
  • Acids proton donor
  • Bases proton acceptor
  • A proton is really just a hydrogen atom that
    has lost its electron!

6
A Brønsted-Lowry acid is a proton donor A
Brønsted-Lowry base is a proton acceptor
conjugate base
conjugate acid
acid
base
7
ACID-BASE THEORIES
  • The Brønsted definition means NH3 is a BASE in
    water and water is itself an ACID

8
Conjugate Pairs
9
Learning Check!
  • Label the acid, base, conjugate acid, and
    conjugate base in each reaction

HCl OH- ?   Cl- H2O
Acid
Base
Conj.Base
Conj.Acid
H2O H2SO4 ?   HSO4- H3O
Conj.Base
Conj.Acid
Acid
Base
10
Acids Base Definitions
Definition 3 Lewis
  • Lewis acid - a substance that accepts an electron
    pair

Lewis base - a substance that donates an electron
pair
11
Lewis Acids Bases
  • Formation of hydronium ion is also an excellent
    example.
  • Electron pair of the new O-H bond originates on
    the Lewis base.

12
Lewis Acid/Base Reaction
13
More About Water
Autoionization
  • Kw H3O OH- 1.00 x 10-14 at 25 oC
  • In a neutral solution H3O OH-
  • and so H3O OH- 1.00 x 10-7 M

14
More About Water
  • H2O can function as both an ACID and a BASE.
  • In pure water there can be AUTOIONIZATION

Equilibrium constant for water Kw Kw 1.00 x
10-14 H3O OH- at 25 oC Take -logs of both
sides 14 pH pOH
15
The pH scale is a way of expressing the strength
of acids and bases. Instead of using very small
numbers, we just use the NEGATIVE power of 10 on
the Molarity of the H3O (or OH-) ion.Under 7
acid 7 neutral Over 7 base
16
Calculating the pH
  • pH - log H3O
  • ((Remember that the mean Molarity or
    concentration)
  • Example If H3O 1 X 10-10
  • pH - log 1 X 10-10
  • pH - (- 10)
  • pH 10
  • Example If H3O 1.8 X 10-5, what is the pH?
  • pH - log 1.8 X 10-5
  • pH - (- 4.74)
  • pH 4.74

17
pH calculations Solving for H3O
  • If the pH of Coke is 3.12, what is the H3O ?
  • Because pH - log H3O then
  • - pH log H3O
  • Take antilog (10x) of both sides and get
  • 10-pH H3O
  • H3O 10-3.12 7.58 x 10-4 M
  • to find antilog on your calculator, look
    for Shift or 2nd function and then the log
    button

18
Strong and Weak Acids/Bases
  • Generally acids and bases are divided into STRONG
    or WEAK ones.
  • Strong acids 6 (HNO3, HCl, HBr, HI, HClO4,
    H2SO4) all others are weak
  • Strong Bases group 1 and 2 hydroxides (all
    others are weak) except Be(OH)2

19
Strong acids and bases
  • Strong acids and bases - are 100 ionized.
  • No equilibrium is set up
  • Acid H30 ( 11 ratio)
  • ACID ?H A H2O ? H3O A-
  • BASE ? B H2O ? BH OH-

pH - log H3O pH - log 0.15 pH - (-
0.82) pH 0.82 pH - log 3 X 10-7 pH - (-
6.52) pH 6.52
Finding pH
  • Find the pH of these
  • A 0.15 M solution of Hydrochloric acid
  • 2) A 3.00 X 10-7 M solution of Nitric acid
  • 3) What is the pH of 0.0034M H2SO4?

20
pH of strong bases
  • What is the pH of the 0.0010 M NaOH
    solution?
  • OH- 0.0010 (or 1.0 X 10-3 M)
  • pOH - log 0.0010
  • pOH 3
  • pH 14 3 11
  • OR Kw H3O OH-
  • H3O 1.0 x 10-11 M
  • pH - log (1.0 x 10-11) 11.00

21
What is the pH of a 2 x 10-3 M HNO3 solution?
HNO3 is a strong acid 100 dissociation.
0.0 M
0.0 M
Start
0.002 M
0.002 M
0.002 M
0.0 M
End
pH -log H -log H3O -log(0.002) 2.7
Ba(OH)2 is a strong base 100 dissociation.
0.0 M
0.0 M
Start
0.018 M
0.018 M
0.036 M
0.0 M
End
pH 14.00 pOH 14.00 - (-log(0.036) ) 12.56
15.4
22
Weak Acids/Bases
  • Weak acids are much less than 100 ionized in
    water.
  • Equilibrium is set up. Common weak acids are
    acetic acid and weak base is ammonia

23
Equilibria Involving Weak Acids and Bases
  • Consider acetic acid, HC2H3O2 (HOAc)
  • HC2H3O2(aq) H2O(l) ? H3O (aq) C2H3O2
    (aq)
  • Acid Conj. base

(K is designated Ka for ACID) K gives the ratio
of ions (split up) to molecules (dont split up)
24
Ionization Constants for Acids/Bases
Conjugate Bases
Acids
Increase strength
Increase strength
25
Equilibrium Constants for Weak Acids
Weak acid has Ka lt 1 Leads to small H3O and a
pH of 2 - 7
26
Equilibrium Constants for Weak Bases
Kb base dissociation constant and is temp
dependent Weak base has Kb lt 1 Leads to small
OH- and a pH of 12 - 7
27
Relation of Ka, Kb, H3O and pH
28
Equilibria Involving A Weak Acid
  • You have 1.00 M HOAc. Calc. the equilibrium
    concs. of HOAc, H3O, OAc-, and the pH.
  • Step 1. Define equilibrium concs. in ICE table.
  • HOAc H3O OAc-
  • initial
  • change
  • equilib

1.00 0 0
-x x x
1.00-x x x
29
Equilibria Involving A Weak Acid
You have 1.00 M HOAc. Calc. the equilibrium
concs. of HOAc, H3O, OAc-, and the pH.
  • Step 2. Write Ka expression

This is a quadratic. Solve using quadratic
formula.
or you can make an approximation if x is very
small! (Rule of thumb 10-5 or smaller is ok)
30
Equilibria Involving A Weak Acid
You have 1.00 M HOAc. Calc. the equilibrium
concs. of HOAc, H3O, OAc-, and the pH.
  • Step 3. Solve Ka expression

First assume x is very small because Ka is so
small.
Now we can more easily solve this approximate
expression.
31
Equilibria Involving A Weak Acid
You have 1.00 M HOAc. Calc. the equilibrium
concs. of HOAc, H3O, OAc-, and the pH.
  • Step 3. Solve Ka approximate expression

x H3O OAc- 4.2 x 10-3 M pH - log
H3O -log (4.2 x 10-3) 2.37
32
Equilibria Involving A Weak Acid
  • Calculate the pH of a 0.0010 M solution of formic
    acid, HCO2H.
  • HCO2H H2O ? HCO2- H3O
  • Ka 1.8 x 10-4
  • Approximate solution
  • H3O 4.2 x 10-4 M, pH 3.37
  • Exact Solution
  • H3O HCO2- 3.4 x 10-4 M
  • HCO2H 0.0010 - 3.4 x 10-4 0.0007 M
  • pH 3.47

33
Equilibria Involving A Weak Base
  • You have 0.010 M NH3. Calc. the pH.
  • NH3 H2O ? NH4 OH-
  • Kb 1.8 x 10-5
  • Step 1. Define equilibrium concs. in ICE table
  • NH3 NH4 OH-
  • initial
  • change
  • equilib

0.010 0 0
-x x x
0.010 - x x x
34
Equilibria Involving A Weak Base
  • You have 0.010 M NH3. Calc. the pH.
  • NH3 H2O ? NH4 OH-
  • Kb 1.8 x 10-5
  • Step 2. Solve the equilibrium expression

Assume x is small, so x OH- NH4
4.2 x 10-4 M and NH3 0.010 - 4.2 x 10-4
0.010 M The approximation is valid !
35
Equilibria Involving A Weak Base
  • You have 0.010 M NH3. Calc. the pH.
  • NH3 H2O ? NH4 OH-
  • Kb 1.8 x 10-5
  • Step 3. Calculate pH
  • OH- 4.2 x 10-4 M
  • so pOH - log OH- 3.37
  • Because pH pOH 14,
  • pH 10.63

36
Percent Ionization for Weak Acids
  • Most weak acids ionize lt 50
  • Percent ionization (p)
  • General Weak Acid HA(aq) H2O(l) ? H3O (aq)
    A- (aq)
  • p varies? depending on concentration increase
    HA decreases p
  • This is caused by Le Chateliers Principle
  • Remember, for strong acids we assume complete
    ionization (100)

37
Examples
The pH of a 0.10mol/L methanoic acid (HCOOH)
solution is 2.38. Calculate the percent
ionization of methanoic acid
Ans 4.2
Calculate the acid ionization constant (Ka )of
acetic acid if a 0.1000mol/L solution at
equilibrium at SATP has a percent ionization of
1.3 (Hint ICE table
Ans 1.7x10-5
38
Relationship Between Ka and Kb for Conjugate Base
Pairs
  • Recall Conjugate Pairs an acid and base that
    differ by one hydrogen
  • Lets consider the hypothetical weak acid, HA, and
    its conjugate base, A -
  • HA (aq) H2O (l) ? H3O (aq) A- (aq)

39
Relationship Between Ka and Kb for Conjugate Base
Pairs
  • Now consider the hypothetical weak base, A- in
    water
  • A- (aq) H2O (l) ? HA (aq) OH- (aq)
  • Now lets put that together
  • HA (aq) H2O (l) ? H3O (aq) A- (aq) ?
    Ka
  • A- (aq) H2O (l) ? HA (aq) OH- (aq)
    ? Kb
  • Add both equations

  • 2H2O (l) ? H3O (aq) OH- (aq)
  • ? Kw

40
Relationship Between Ka and Kb for Conjugate Base
Pairs
Recall Autoionization of water H2O(l)
H2O(l) ? H3O(aq) OH-(aq)
Kw1.00x10-14 must remember this value
41
Relationship Between Ionization Constants for
Conjugate Base Pairs
  • For acids and bases whose chemical formulas
    differ by only one hydrogen (conjugate pairs) the
    following apply
  • Kw Ka x Kb
  • Kb Kw/Ka
  • Ka Kw/Kb
  • Therefore if only the Ka value is available in
    the table, we can determine the conjugate pairs
    Kb by using the above equations
  • Note these equations show the larger the Ka the
    smaller the Kb
  • Stronger acid ? weaker conjugate base
  • Weaker acid ? stronger conjugate base

42
Learning check!
1. What is the value of the base ionization
constant (Kb) for the acetate ion, C2H3O2- (aq)
Ans 5.6x10-10
2. Calculate the percent ionization of propanoic
acid, HC3H5O2(aq), if a 0.050 mol/L solution has
a pH of 2.78
Ans. 3.3
43
Rapid changes in pH can kill fish and other
organisms in lakes and streams. Soil pH is
affected and can kill plants and create sinkholes
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
About PowerShow.com