Volumetric Analysis
Titration
Dr.Riham Hazzaa
• Titration is a common laboratory
method of quantitative chemical analysis
that is used to determine the unknown
concentration of a known reactant.
• Because volume measurements play a
key role in titration, it is also known as
volumetric analysis.
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• Standard solution is a chemical term which
describes a solution of known concentration.
• Primary Standard: Substances whose exact
solution concenteration can be determined by
transferring a known weight of the reagent to a
volumetric flask and diluting to the mark with
solvent
• Secondary standard: A titrant is prepared in an
approximate concentration and then titrated against
a primary standard to determine its exact
concenteration
• Standardization process of calibrating the
secondary standard against our primary standard
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•
• Molarity: is defined as the number of
moles of solute divided by the number of
liters of solution containing the solute.
M = Amount of moles of solute
liters of solution
Amount of moles of solute = Weight
MW
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• Normality: is defined as the number of
equivalents (eq) of solute divded by the
number of liters of solution containing the
solute.
N = Amount of equivalent(eq) of solute
Liters of solution
Amount of equivalents (eq) = weight (grams)
EW
Equivalent weight= Molecular weight
Z
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Normality is related to molarity:
• M = Weight
OR
MW = Weight
MW×volume
M×volume
• N = Weight
OR
EW = Weight
EW×volume
N×volume
• Equivalent weight = Molecular weight
Z
Weight
×Z =
Weight
N×volume
M ×volume
• Thus, Normality (N) = Molarity (M)  (Z)
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• Normality is related to molarity:
• Normality (N) = Molarity (M)  (Z)
• 1M sulfuric acid H2SO4 is 2N for acidbase reactions because each mole of
sulfuric acid provides 2 moles of H+
ions (Z).
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After Dilution
Before Dilution
Solution1
M1 =
Solution2
moles1
litre1
M2 =
moles2
litre2
moles1 = moles2
M1 × litre1 = M2 × litre2
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Acids and Bases
Titration
Properties of Acids
• An acid is any substance that releases hydrogen
ions, H+, into water.
• Blue litmus paper turns red in the presence of
hydrogen ions. Blue litmus is used to test for
acids.
• Acids have a sour taste; lemons, limes, and
vinegar are acidic.
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Properties of Bases
• A base is a substance that releases hydroxide
ions, OH –, into water.
• Red litmus paper turns blue in the presence of
hydroxide ions. Red litmus is used to test for
bases.
• Bases also have a bitter taste; soapy feel.
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Neutralization Reactions
• If we have an acid with two hydrogens (sulfuric acid,
H2SO4), we need two hydroxide ions to neutralize it.
H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + 2 H2O(l)
H2SO4(aq) + Ca(OH)2(aq) → CaSO4(aq) + 2 H2O(l)
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Acid-Base Reactions with Gas Formation
1. Carbonates react with acids to form CO2,
carbon dioxide gas.
NaCO3+ 2HCl → 2NaCl + H2O +CO2
2. Sulfites react with acids to form SO2,
sulfur dioxide gas.
Na2SO3 2HCl → 2NaCl + H2O + SO2
3. Sulfides react with acids to form H2S,
hydrogen sulfide gas.
Na2S + 2HCl → 2NaCl + H2S
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Acid/Base Neutralization
• An acid and a base react with each other in a
neutralization reaction.
• When an acid and a base react, water and a salt
are produced.
• For example, nitric acid reacts with sodium hydroxide
to produce sodium nitrate and water:
HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O(l)
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The pH Scale
• A pH value expresses the acidity or basicity of a
solution.
• Most solutions have a pH between 0 and 14.
• Acidic solutions have a pH less than 7.
– As a solution becomes more acidic, the pH decreases.
• Basic solutions have a pH greater than 7.
– As a solution becomes more basic, the pH increases.
pH = –log[H+]
[H+] = 10–pH
[H+] is the molar hydrogen ion concentration
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Acid/Base Classifications of Solutions
• Strongly acidic solutions
have a pH less than 2.
• Weakly acidic solutions have
a pH between 2 and 7.
• Weakly basic solutions have
a pH between 7 and 12.
• Strongly basic solutions have
a pH greater than 12.
• Neutral solutions have a pH
of 7.
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Acid – base theories
1. Arrhenius theory
2. The Brønsted –Lowry theory
3. Lewis theory
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Arrhenius Theory
• Svante Arrhenius proposed the following
definitions for acids and bases in 1884:
– An Arrhenius acid is a substance that ionizes in water
to produce hydrogen ions.
– An Arrhenius base is a substance that ionizes in water
to release hydroxide ions.
• For example: HCl is an Arrhenius acid
NaOH is an Arrhenius base.
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Strengths of Acids
• Acids have varying strengths.
• The strength of an Arrhenius acid is measured by
the degree of ionization in solution.
• Ionization is the process where polar compounds
separate into cations and anions in solution.
• The acid HCl ionizes into H+ and Cl– ions in
solution.
HCl + H2O → H3O+ + Clhydronium ions
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Arrhenius Acids in Solution
• All Arrhenius acids have a hydrogen atom bonded
to the rest of the molecule by a polar bond. This
bond is broken when the acid ionizes.
• Polar water molecules help ionize the acid by
pulling the hydrogen atom away:
HCl(aq) + H2O(l) → H3O+(aq) + Cl–(aq) (~100%)
HC2H3O2(aq) + H2O(l) → H3O+(aq) + C2H3O2–(aq) (~1%)
• The hydronium ion, H3O+, is formed when the
aqueous hydrogen ion attaches to a water molecule.
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Strong & Weak Arrhenius Acids
• Strong acids ionize extensively (completly) to
release hydrogen ions into solution.
– HCl is a strong acid and ionizes nearly 100%
• Weak acids only ionize slightly(partialy )in
solution.
– HF is a weak acid and ionizes only about 1%
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Strengths of Bases
• Bases also have varying strengths.
• The strength of an Arrhenius base is measured by
the degree of dissociation in solution.
• Dissociation is the process where cations and
anions in an ionic compound separate in solution.
• A formula unit of NaOH dissociates into Na+ and
OH– ions in solution.
NaOH  Na+ + OHDr.Riham Hazzaa
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Arrhenius Bases in Solution
• When we dissolve Arrhenius bases in solution,
they dissociate giving a cation and a hydroxide
anion.
• Strong bases dissociate almost fully and weak
bases dissociate very little:
NaOH(aq) → Na+(aq) + OH–(aq) (~100%)
NH4OH(aq) ↔ NH4+(aq) + OH–(aq) (~1%)
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Strong & Weak Arrhenius Bases
• Strong bases dissociate extensively to release
hydroxide ions into solution.
– NaOH is a strong base and dissociates nearly 100%
• Weak bases only ionize slightly in solution.
– NH4OH is a weak base and only partially dissociates
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Brønsted-Lowry Theory
• The Brønsted-Lowry definitions of acids and
bases are broader than the Arrhenius definitions.
• A Brønsted-Lowry acid is a substance that
donates a hydrogen ion to any other substance. It
is a proton donor.
• A Brønsted-Lowry base is a substance that
accepts a hydrogen ion. It is a proton acceptor.
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Brønsted-Lowry Acids & Bases
• Lets look at two acid/base reactions:
– HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
– HCl(aq) + NH3(aq) → NH4Cl(aq)
• HCl donates a proton in both reactions and is a
Brønsted-Lowry acid.
• In the first reaction, the NaOH accepts a proton
and is the Brønsted-Lowry base.
• In the second reaction, NH3 accepts a proton and is
the Brønsted-Lowry base.
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Amphiprotic Compounds
• A substance that is capable of both donating and
accepting a proton is an amphiprotic compound.
• NaHCO3 is an example:
– HCl(aq) + NaHCO3(aq) → NaCl(aq) + H2CO3(aq)
– NaOH(aq) + NaHCO3(aq) → Na2CO3 (aq) + H2O(l)
• NaHCO3 accepts a proton from HCl in the first
reaction and donates a proton to NaOH in the
second reaction.
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Lewis Theory
Lewis acid-base theory relates acid-base behavior of
molecules to their molecular structure.
Lewis acid- A species that is an electron pair acceptor.
Lewis base- A species that is an electron pair donor.
H+ + :NH3  H:NH3+
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Acid-Base Titrations
• A titration is used to analyze an
acid solution using a solution of a
base.
• A measured volume of base is
added to the acid solution. When all
of the acid has been neutralized, the
pH is 7. One extra drop of base
solution after the endpoint increases
the pH dramatically.
• When the pH increases above 7,
phenolphthalein
changes
from
colorless to pink indicating the
endpoint of the titration.
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Acid-Base Indicators
Methyl Red
Bromothymol Blue Phenolphthalein
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Acid-Base Titrations:
Strong Acid/Strong Base
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
?M
KNOWN M
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Titration curve
14
Fewer moles of H2SO4
would be required to
neutralize 25 mL NaOH,
thus the curve would shift
left
7
0
0
Because we start with
pure HCl, then add NaOH
the pH starts low then
goes high, thus the curve
flips
25
50
14
7
0
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0
25
33
50
The theory
• Begin with a balanced equation for the
reaction:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
na = 1
nb = 1 (mole ratios of acid and base)
Mole = concentration X volume
For the acid: na = MaVa
For the base: nb = MbVb
na :
nb (stoichiometry mole ratio)
MaVa
:
Mb V b
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Dr.Riham Hazzaa
The Theory
i.e.
Then,
na :
MaVa
na
=
MaVa
MaVa
=
Mb V b
MaVa =
nb
:
Mb V b
nb
Mb V b
na
nb
na MbVb
nb
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Titration Problem
1.What is the molarity of a hydrochloric acid
solution if 25.50 mL are required to neutralize 0.375
g Na2CO3?
2 HCl(aq) + Na2CO3(aq) → 2 NaCl(aq) + H2O(l) + CO2(g)
the molarity of a hydrochloric acid = 0.277 M HCl
2. A 10.0 mL sample of 0.555 M H2SO4 is titrated
with 0.233 M NaOH. What volume of NaOH is
required for the titration?
H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + H2O(l)
volume of NaOH = 49.8 mL NaOH
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