Hourly I (November 4)
E4 Acids, Bases, and Salts
Oct. 29 - Nov. 4
Review Notes
• Posted on CTools and course website
Session two goals
Review Sessions
• Saturday, Nov. 1, 10am - noon, 1800 chem.
♦ 10-10:40 am: Experiment 1
♦ 10:40 - 11:20 am: Experiment 2
♦ 11:20 - noon: Experiment 3
 Complete E4, Parts 3 - 5.
 Complete the team report
and discussion presentation.
• Monday, Nov.3, 6 - 8 pm, 140 Lorch Hall
♦ Question and answers
Acid - Base Neutralization (Parts 3 - 5)
Neutralization:
CH3COOH + NaOH →
acid
+ base
→
CH3COONa + HOH
salt
+
water
Acid-Base Neutralization
Example:
CH3COOH + NaOH
CH3COONa + HOH
• Adding base to a weak acid drives the reaction
(donation of proton/s) to completion
• At neutralization, only the products (salt and
water) are present.
HCl(g) + NH3(g) →
NH4Cl(s)
DEMO
Carboxylic Acids (Parts 3 - 5)
Neutralization Reaction Stoichiometry
 Reaction stoichiometry is dependant on the number
of ionizable protons.
Carboxylic acids
C-based weak acids containing the
group
Acetic acid (Part 3):
CH3COOH + NaOH → CH3COONa
1 mol
+ HOH
1 mol
Oxalic acid (Part 4):
HOOC-COOH + 2 NaOH → 2COONa + 2HOH
1 mol
2 mol
1
Carboxylic Acids and Ionizable Protons
Electronegativity of the elements*
1
2
3
4
5
6
7
8
IA IIA IIIB IVB VB VIB VIIB
9
VIIIB
10
11
IB
Carboxylic acids
12 13 14 15 16 17
IIB IIIA IVA VA VIA VIIA
H
2.1
Li Be
B C N O F
1.0 1.5
2.0 2.5 3.0 3.5 4.0
Na Mg
Al Si P S Cl
0.9 1.2
1.5 1.8 2.1 2.5 3.0
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br
0.8 1.0 1.3 1.5 1.6 1.6 1.5 1.8 1.8 1.8 1.9 1.6 1.6 1.8 2.0 2.4 2.8
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I
0.8 1.0 1.2 1.4 1.6 1.8 1.9 2.2 2.2 2.2 1.9 1.7 1.7 1.8 1.9 2.1 2.5
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At
0.7
The0.9electronegativity
H and
and1.9
therefore
in the
-Lu 1.3 1.5 1.7 of1.9
2.2 O
2.2differ
2.2 2.4
1.8 1.8H1.9
2.0 2.2
COOH
Fr Ra group
Ac This ionizable.
Pa U Np- N o
1.1 1.3 1.5 1.7of H and
1.3 C are similar and therefore C-H
0.7
The0.9
electronegativity
•
•
H
|
O
||
Part 3: Acetic acid
HC2H3O2
• H− C − C − O − H
•
|
•
H
•
•
O O
|| ||
•H − O− C − C − O − H
CH3COOH
Carboxylic group containing
one ionizable proton
Part 4: Oxalic acid
H2C2O4
HOOCCOOH
Two carboxylic groups each
with one ionizable proton
= Metalloids
Metals
bonds
are stable and= Nonmetals
H in the C-H =bond
is NOT ionizable
Q. How many mL of 0.10 M NaOH will be required
to neutralize 5.0 mL of 0.10 M oxalic acid?
Titration (Parts 3 -5)
Oxalic acid
HOOC-COOH + 2 NaOH → 2COONa + 2HOH
• 2 mol of NaOH is required to neutralize one mol of
oxalic acid:
2 (mmol acid) = mmol base
2 (5.0 mL • 0.10 M) = x mL • 0.10 M
= 10 mL of 0.10 M NaOH
DEMO
Part 3 Acid-Base Neutralizations and Indicators
Base delivered
from burette
Indicator color change
signals the end-point
or neutralization
Titration (Parts 3)
 Compare the use of indicators for monitoring the
neutralization of acetic acid with sodium hydroxide
Experiment variable:
• Indicators
Experiment constants
• Acid identity, concentration, and volume
• Base identity and concentration
DEMO
2
Indicator pH End Points
Indicator End Point pH
 The pH interval at which the indicator changes
color
Acids are colorless Bases are pink
Phenolphthalein: pH 8.2
- pH 10.1
↑
pH 9.1
 The indicator color change is observable at the
mid-point of the end point pH range.
 Indicators have different end-point pH color changes
 For information on lab indicators, see the lab manual, p. 194
Equivalence Point pH
Titration and Indicator pH End Points
 The pH of the salt and water products of the acid-base
neutralization reaction = the equivalence point pH.
CH3COOH + NaOH → CH3COONa + HOH
Equivalence point pH
≈ pH 8
“Ideally, the indicator end point pH equals the
equivalence point pH = pH 8. “
DEMO
Part 5. Identification of an Unknown Acid
• Identify a carboxylic acid from melting point
and equivalent weight data
• The melting point range will be determined
using a melting point apparatus
• The equivalent weight will be determined by
titrating a known mass of the acid with NaOH
See Table, p.118
Name
2-hydroxybenzoic
acid acetate
Formula
COOH
MW EW MP
180 180 135
OCOCH3
trans-cinnamic acid
CH
CH COOH
Cl
2-chlorobenzoic acid
148 148
135136
157 157
140
COOH
cis-butenedioic
(maleic) acid
H
HOOC
H
COOH
116
58 139140
3
Part 5. Identification of an Unknown Acid
•
•
•
Practice melting point and equivalent weight skills
with known compounds BEFORE attempting to
identify the unknown
Determine the approximate range of the unknown’s
melting point (e.g., 110 -130ºC) BEFORE
determining the actual melting point range.
Note: Unknown melting points 99°C - 200°C
Equivalent Weight (EW)
 Mass (grams) of compound providing one mole of H+
 EW = Molecular Wt/# ionizable protons
Examples:
H2SO4 = molecular weight of 98
H2SO4 = equivalent weight of 49
Determine the approximate volume of NaOH
needed to neutralize the unknown acid BEFORE
determining the volume quantitatively
EW of Oxalic Acid (Part 4)
Q. What is the equivalent weight of oxalic acid?
Oxalic acid: MW = 90.04
HOOC-COOH + 2 NaOH → 2COONa + 2HOH
0.5 mol
1 mol
45.02 g
HCl = molecular weight of 36.5
HCl = equivalent weight of 36.5
Carboxylic Acid Structure and Equivalent Weight
Benzoic acid
•
•
•
•
•
COOH
 One ionizable proton.
1 mol (or 1000 mmol)
Benzoic acid = C 6 H5COOH
MW = EW
 No ionizable protons.
 Not an acid.
•
O H H H H O
Adipic acid
•
||
|
|
|
|
||
HOOC(CH 2 )4COOH
H-O−C−C−C−C−C−C−O−H
•
|
|
|
|
•
H H H H
Two ionizable protons.
Molecular Weight = 146
73
Equivalent weight = _____________?
Q. An acid has an equivalent weight (EW) of 88.92. The
EW = molecular wt/#ionizable protons. List the number
of any compound from the table that may be the acid.
1.
2.
3.
4.
Compound
Ethanoic acid
Butanoic acid
Oxalic acid
1-methyl, 1,2 benzene
dicarboxylic acid
Formula
CH3COOH
CH3CH2CH2COOH
HOOC-COOH
CH3C6H3(COOH)2
MW
60
88
90
180
Answer. Compounds # 2 and # 4.
4
A teammate titrates a carboxylic acid and calculates
the EW of the acid to be 72.50. The result is correct
within 2%. The MW of the acid = 1.5 x 102
A. How many ionizable protons/mol are in the acid?that
EW from Experiment Data
 Determine the equivalent weight of an unidentified
carboxylic acid by titration
•
Let X = # ionizable protons.
EW = 72.50 = MW/X = 150/X
X= ~ 2
B. Circle each structure that is consistent with the data.
Adipic Acid, MW = 146:
HO2CCH 2CH2CH2CH2CO2H
Trans-cinnamic acid, MW=148
-CH=CH-COOH
Citric Acid, MW = 192:
HO2C-CH2-C(OH)-CH 2-CO2H

CO 2H
• EW = Mass (g) of acid providing 1 mol H+
or neutralizing 1 mol OH-.
EW =
mass acid (g)
moles of OH- neutralized
Oxalic acid, MW = 90
HO 2C—CO2H
EW from Experiment Data (Part 5)
EW of Oxalic Acid (Part 4)
 Determine the EW of an acid by titration
Q. 10.0 mL of 1.0 M NaOH neutralizes 0.4502
grams of an unknown acid. What is the equivalent
weight of the acid?
Answer.
Fact: 0.4502 g neutralized 10.0 mmol of NaOH.
The mass of acid needed to neutralize 1 mol =
45.02g = EW
Q.
You titrate 0.175 g of an acid. 30.00 mL of 0.10 M
NaOH neutralizes the sample.
1) What is the acid’s EW based on the data?
2) Identify the acid from the list below.
Name
2-hydroxybenzoic acid acetate
Formula
COOH
OCOCH3
trans-cinnamic acid
CH CH COOH
2-chlorobenzoic acid
cis-butenedioic (maleic) acid
Cl
H
HOOC
COOH
H
MW
180
MP
135
148
135-136
157
140
116
139-140
Equivalent weight determination.
1) Determine mol of NaOH the acid has neutralized.
Fact: The acid mass neutralized 30.00 mL of 0.10 M NaOH
mol OH- = V(L)
x M NaOH
= 0.0300L x 0.10 mol
L
= 3.0 x 10-3 mol
COOH
5
Equivalent Weight determination.
2) Determine the mass of acid that would
neutralize one mol of hydroxide ions.
Known:
0.175 g
X g acid
=
0.0030 mol OH1 mol OH-
X = 58 g
Q. What is the identity of the acid?
Name
2-hydroxybenzoic acid acetate
Formula
COOH
OCOCH3
trans-cinnamic acid
CH CH COOH
2-chlorobenzoic acid
cis-butenedioic (maleic) acid √
Cl
H
HOOC
COOH
H
MW
180
MP
135
148
135-136
157
140
116
139-140
COOH
Questions?
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