Download Unit 9: ACIDS AND BASES

Unit 9: ACIDS AND BASES
CDO IB Chemistry SL/HL
I.
II.
III.
IV.
Acid Base Theories
a. Define acids and bases accordingto the Brønsted–Lowry and Lewis theories.
b. Deduce whether or not a species could act as a Brønsted–Lowry and/or a Lewis acid or
base.
c. Deduce the formula of the conjugateacid (or base)
Properties of Acids and Bases
a. Outline the characteristic properties of acids and bases in aqueous solution.
Strong and Weak Acids
a. Distinguish between strong and weak acids and bases in terms of the extent of
dissociation, reaction with water and electrical conductivity.
b. State whether a given acid or base is strong or weak.
c. Distinguish between strong and weak acids and bases, and determine the relative
strengths of acids and bases, using experimental data.
The pH Scale
a. Distinguish between aqueous solutions that are acidic, neutral or alkaline using the pH
scale.
b. Identify which of two or more aqueous solutions is more acidic or alkaline using pH
values.
c. State that each change of one pH unit represents a 10-fold change in the hydrogen ion
concentration [H+(aq)].
d. Deduce changes in [H+(aq)] when the pH of a solution changes by more than one pH
unit.
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
Assessment Statements
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Common Experiences with Acids and Bases
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Acids
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Sour Taste
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Bases
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Bitter Taste
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Common Experiences with Acids and Bases
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Acids
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React
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Are often used in
Bases
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Feel
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Reacts with
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Are in many
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Drain
Reactions of acids with metals
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Acids react with metals to produce a salt and hydrogen gas:
Reactions of acids with Oxides
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Acids react with
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Example
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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Reactions of acids with Carbonates
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Acids react with
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Example
Defining Acids and Bases
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Arrhenius
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Acids dissolve in water to produce H+ ions
ex:
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Bases dissolve in water to produce OH- ions
ex:
Problems with Arrhenius
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Only true for bases that
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There are bases that do not always have OH ions,
Only true for
Defining Acids and Bases
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Lewis Acids
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Lewis acids are defined
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Atoms with an empty
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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Lewis Bases
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Lewis bases are defined
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The Lewis Definition
Examples of Lewis acid bases
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NH3 + H+ 
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Lewis Bases: NH3 and Water –
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Lewis Acids: H+ and BX3 (X = Halogen)
Defining Acids and Bases
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Brønsted-Lowry
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An acid is a proton donor.
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o
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This is the same as Arrhenius
A base is a proton acceptor.
This definition works for most acid base reactions for we use it most of the
time
If it can do either…
…it is amphiprotic.
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What Happens When an Acid Dissolves in Water?
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Water acts as a Brønsted-Lowry
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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Conjugate Acids and Bases
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The term conjugate comes from the Latin word “conjugare,”
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Reactions between acids and bases
Example 1: Conjugate Acid Base Pairs
HCl(aq) + H2O (l)  Cl-(aq) + H3O+(aq)
NH3(aq) + H2O  NH4+(aq) + OH-(aq)
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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As a result, the
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Acid Strength
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Strong acids are completely
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Their conjugate bases
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Example:
HA + H2O 
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Weak acids only
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Their conjugate bases are weak bases.
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Example
HA + H2O 
Reactant Favored Reactions!
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BASE Strength
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Strong bases completely
Ex: NaOH 
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Weak bases only
Ex: NH3 + H2O 
Strong and weak to know
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STRONG
WEAK
MEMORIZE THESE
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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Distinguishing between strong and weak acids and bases
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Solutions of strong acids and bases
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Strong acids have a
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Strong bases have a
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Strong acids react more
Strength vs concentration
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Concentration refers to the number of
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Strength refers to how much the acid or base dissociates
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pH
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Used to indicate is a
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pH scale
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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pH
Common substance pH
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Calculating pH
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pH is defined as the negative base-10 logarithm of the concentration of hydronium ion
(hydrogen ion)
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Finding hydronium or hydrogen ion concentration from pH
Features of the pH Scale
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pH numbers are usually
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pH is inversely related to the concentration of [H3O+] –
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A change in pH indicates
How Do We Measure pH?
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For less accurate measurements, one can use
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Litmus paper
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“Red”
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“Blue”
Or an
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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How Do We Measure pH?
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For more accurate measurements,
Relationship between H3O+ and OH
Acid
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Neutral
[
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Alkaline (Basic)
Finding ph in Strong acids and Bases
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Strong acids –
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Strong Bases –
exception
AND
Example 4: Calculating pH
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Find the pH of a 0.10 M solution of HCl.
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Find the pH of a 0.10 M solution of NaOH?
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Find the pH of a 0.10 M solution of Ca(OH)2
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
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Problem Set 9-1
1. Complete and Balance the following chemical equations:
a. HNO3(aq) + NaHCO3(aq) 
b. Al2O3(aq) + HCl(aq) 
c. ZnO(s) + H2SO4(aq) 
d. Mg(s) + HNO3(aq) 
e. H2SO4(aq) + CuCO3(s) 
f. HCl(aq) + Ca(OH)2(aq) 
2. Define an acid according to the Bronsted-Lowry and Lewis definitions.
3. Write an equation between ammonia and ethanoic acid (acetic acid CH3COOH) classifying each
species as an acid or a base.
4. Give the formula of the conjugate acid for each of the following: (HINT: Add a H!)
a. NH3
d. CNb. OHe. HPO42c. HSO45. Give the formula an the conjugate base of each of the following: (Hint: Remove an H)
a. HCO3c. HCOOH
b. H2O
d. NH3
6. In each of the following reactions state whether the species in BOLD is acting as an acid or a
base according to the Bronsted Lowry definition
a. HSO4- + H2O  SO42- + H3O+
b. HCO3- + HSO4-  H2CO3 + SO42c. CH3COOH + H2SO4  CH2COOH2+ + HSO47. Classify each of the following as a substance that can act as a Lewis acid or is a Lewis base
H2O
BF3
HCO3H+
AlCl3
NH3
CO
8. Complete and balance the following equations:
a. Zn + H2SO4 
b. CuO + HNO3 
c. NH3 + H2SO4 
d. Ca(HCO3)2 + HCl 
e. Mg(OH)2 + H2SO4 
f. Cu + H2SO4 
g. CaO + HCl 
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
Unit 9: Introduction to Acids and Bases
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Problem Set 9-2
1. Classify each of the following as a strong acid, weak acid, strong base, weak base or salt
HCl
H2SO4
NH4NO3
NaOH
NH3
HNO3
Na2SO4
H2CO3
Ba(OH)2
KNO3
CH3NH2
CH3COOH
2. For each pair of solutions state which will have a higher conductivity
a. 0.10 mol dm-3 CH3COOH and 0.10 mol dm-3 HCl
b. 0.10 mol dm-3 NH3 and 0.10 mol dm-3 KOH
c. 0.10 mol dm-3 HCl and 0.10 mol dm-3 H2SO4
d. 0.10 mol dm-3 HNO3 and 0.10 mol dm-3 HCl
3. Arrange the following in order of increasing pH
1.0 mol dm-3 NH3
0.010 mol dm-3 HCl
1.0 mol dm-3 NaOH
0.001 mol dm-3 CH3CH2COOH 0.10 mol dm-3 H2SO4
0.010 mol dm-3 CH3CH2COOH
0.0010 mol dm-3 NH3
0.10 mol dm-3 HCl
4. State whether each of the following statements is true or flase?
a. The pH of a 0.10 mol dm-3 HCl is 2
b. The [H+] is a solution of pH = 3 is 100 times the [H+] in a solution of pH = 5
c. The [H+] in a solution of pH = 13 is 1.0 x 1013 mol dm-3
5. Calculate each of the following
a. What is the pH of a solution that has a [H3O+] of 2.3 x 10-9 M?
b. What is the pH of a solution that has a [HCl] = 1.50 x 10-3 M?
c. What is the M of a HCl solution that has a pH of 3.500?
d. What is the M of a HI solution that has a pH of 1.60?
e. What is the pH of a NaOH solution that has a [H3O+] of 1.0 x 10-11 M?
6. A solution of a 0.2 mol dm-3 HCl has a pH of 0.7. Of this solution 25.0 cm3 is taken and made up to a total
volume of 250 cm3 with distilled water to form solution X. 10.0 cm3 of solution X is taken and made up to a
total form of 1.00 dm3 (same as a L) with distilled water in a volumetric flask, this is solution Y.
a. Work out the pH value for each solution
b. Suggest an experimental method other than measuring the pH or using an indicator that could be
used to distinguish between solution X and solution Y
Unit 8 CDO IB Chemistry SL :Acids and Bases Christman
Unit 9: Strong and Weak pH
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