hourly i (november 4) - umich.edu
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Hourly I (November 4)Hourly I (November 4)
Review Notes
• Posted on CTools and course website
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
• Monday, Nov.3, 6 - 8 pm, 140 Lorch Hall ♦ Question and answers
E4 Acids, Bases, and SaltsOct. 29 - Nov. 4
E4 Acids, Bases, and SaltsOct. 29 - Nov. 4
Session two goals Complete E4, Parts 3 - 5.
Complete the team reportand discussion presentation.
Acid - Base Neutralization (Parts 3 - 5)Acid - Base Neutralization (Parts 3 - 5)
Neutralization:
acid + base → salt + water
DEMO
CH3COOH + NaOH → CH3COONa + HOH
HCl(g) + NH3(g) → NH4Cl(s)
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Acid-Base NeutralizationAcid-Base Neutralization
• Adding base to a weak acid drives the reaction(donation of proton/s) to completion
Example:CH3COOH + NaOH CH3COONa + HOH
• At neutralization, only the products (salt andwater) are present.
Carboxylic Acids (Parts 3 - 5)Carboxylic Acids (Parts 3 - 5)
Carboxylic acids
C-based weak acids containing the group
Neutralization Reaction StoichiometryNeutralization Reaction Stoichiometry
Reaction stoichiometry is dependant on the numberof ionizable protons.
Acetic acid (Part 3):CH3COOH + NaOH → CH3COONa + HOH
1 mol 1 mol
Oxalic acid (Part 4):HOOC-COOH + 2 NaOH → 2COONa + 2HOH1 mol 2 mol
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Electronegativity of the elements* 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA H 2.1
Li 1.0
Be 1.5
B 2.0
C 2.5
N 3.0
O 3.5
F 4.0
Na 0.9
Mg 1.2
Al 1.5
Si 1.8
P 2.1
S 2.5
Cl 3.0
K 0.8
Ca 1.0
Sc 1.3
Ti 1.5
V 1.6
Cr 1.6
Mn 1.5
Fe 1.8
Co 1.8
Ni 1.8
Cu 1.9
Zn 1.6
Ga 1.6
Ge 1.8
As 2.0
Se 2.4
Br 2.8
Rb 0.8
Sr 1.0
Y 1.2
Zr 1.4
Nb 1.6
Mo 1.8
Tc 1.9
Ru 2.2
Rh 2.2
Pd 2.2
Ag 1.9
Cd 1.7
In 1.7
Sn 1.8
Sb 1.9
Te 2.1
I 2.5
Cs 0.7
Ba 0.9
La -Lu
Hf 1.3
Ta 1.5
W 1.7
Re 1.9
Os 2.2
Ir 2.2
Pt 2.2
Au 2.4
Hg 1.9
Tl 1.8
Pb 1.8
Bi 1.9
Po 2.0
At 2.2
Fr 0.7
Ra 0.9
Ac 1.1
Th 1.3
Pa 1.5
U 1.7
Np-
N o 1.3
= Metalloids = Nonmetals = Metals
Carboxylic Acids and Ionizable Protons
The electronegativity of H and C are similar and therefore C-Hbonds are stable and H in the C-H bond is NOT ionizable
The electronegativity of H and O differ and therefore H in theCOOH group is ionizable.
Carboxylic acidsCarboxylic acids
• H O Part 3: Acetic acid• | || HC2H3O2
• H− C − C − O − H CH3COOH• |• H
Carboxylic group containingone ionizable proton
• O O Part 4: Oxalic acid• || || H2C2O4
•H − O− C − C − O − H HOOCCOOH Two carboxylic groups each
with one ionizable proton
Q. How many mL of 0.10 M NaOH will be requiredto neutralize 5.0 mL of 0.10 M oxalic acid?Q. How many mL of 0.10 M NaOH will be requiredto neutralize 5.0 mL of 0.10 M oxalic acid?
Oxalic acidHOOC-COOH + 2 NaOH → 2COONa + 2HOH
2 (mmol acid) = mmol base2 (5.0 mL • 0.10 M) = x mL • 0.10 M
• 2 mol of NaOH is required to neutralize one mol ofoxalic acid:
= 10 mL of 0.10 M NaOH
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Titration (Parts 3 -5)Titration (Parts 3 -5)
Base delivered Indicator color changefrom burette signals the end-point or neutralizationDEMO
Part 3 Acid-Base Neutralizations and IndicatorsPart 3 Acid-Base Neutralizations and Indicators
Compare the use of indicators for monitoring theneutralization of acetic acid with sodium hydroxide
Experiment variable:• Indicators
Experiment constants• Acid identity, concentration, and volume• Base identity and concentration
DEMO
Indicator pH End PointsIndicator pH End Points
Indicators have different end-point pH color changes
For information on lab indicators, see the lab manual, p. 194
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Indicator End Point pHIndicator End Point pH
The pH interval at which the indicator changescolor
↑pH 9.1
Acids are colorless Bases are pink
The indicator color change is observable at themid-point of the end point pH range.
Phenolphthalein: pH 8.2 - pH 10.1
Titration and Indicator pH End PointsTitration and Indicator pH End Points
Equivalence Point pHEquivalence Point pH
The pH of the salt and water products of the acid-baseneutralization reaction = the equivalence point pH.
CH3COOH + NaOH → CH3COONa + HOH
“Ideally, the indicator end point pH equals theequivalence point pH = pH 8. “
DEMO
Equivalence point pH ≈ pH 8
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Part 5. Identification of an Unknown AcidPart 5. Identification of an Unknown Acid
• Identify a carboxylic acid from melting pointand equivalent weight data
• The melting point range will be determinedusing a melting point apparatus
• The equivalent weight will be determined bytitrating a known mass of the acid with NaOH
139-140
116cis-butenedioic(maleic) acid
1401572-chlorobenzoic acid
135-136
148trans-cinnamic acid
1351802-hydroxybenzoicacid acetate
MPEWMWFormulaSee Table, p.118
Name
COOH
OCOCH3
CH CH COOH
Cl
COOH
H HHOOC COOH
180
148
157
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Part 5. Identification of an Unknown AcidPart 5. Identification of an Unknown Acid
• Practice melting point and equivalent weight skillswith known compounds BEFORE attempting toidentify the unknown
• Determine the approximate range of the unknown’smelting point (e.g., 110 -130ºC) BEFOREdetermining the actual melting point range.Note: Unknown melting points 99°C - 200°C
• Determine the approximate volume of NaOHneeded to neutralize the unknown acid BEFOREdetermining the volume quantitatively
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Equivalent Weight (EW)Equivalent Weight (EW)
Mass (grams) of compound providing one mole of H+
EW = Molecular Wt/# ionizable protons
Examples:H2SO4 = molecular weight of 98H2SO4 = equivalent weight of 49
HCl = molecular weight of 36.5HCl = equivalent weight of 36.5
EW of Oxalic Acid (Part 4) EW of Oxalic Acid (Part 4)
Oxalic acid: MW = 90.04HOOC-COOH + 2 NaOH → 2COONa + 2HOH0.5 mol 1 mol45.02 g 1 mol (or 1000 mmol)
Q. What is the equivalent weight of oxalic acid?
Carboxylic Acid Structure and Equivalent WeightCarboxylic Acid Structure and Equivalent Weight
• Benzoic acid• COOH• ••
No ionizable protons. Not an acid.
One ionizable proton.
Benzoic acid = C6 H5COOH
MW = EW
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• O H H H H O Adipic acid• | | | | | | | | HOOC(CH2 )4COOHH - O − C − C − C − C − C − C − O − H • | | | |• H H H H
Two ionizable protons.
Molecular Weight = 146Equivalent weight = _____________?
Q. An acid has an equivalent weight (EW) of 88.92. TheEW = molecular wt/#ionizable protons. List the numberof any compound from the table that may be the acid.
Compound Formula MW1. Ethanoic acid CH3COOH 602. Butanoic acid CH3CH2CH2COOH 883. Oxalic acid HOOC-COOH 904. 1-methyl, 1,2 benzene
dicarboxylic acidCH3C6H3(COOH)2 180
Answer. ________________
A teammate titrates a carboxylic acid and calculatesthe EW of the acid to be 72.50. The result is correctwithin 2%. The MW of the acid = 1.5 x 102
A teammate titrates a carboxylic acid and calculatesthe EW of the acid to be 72.50. The result is correctwithin 2%. The MW of the acid = 1.5 x 102
A. How many ionizable protons/mol are in the acid?that•
B. Circle each structure that is consistent with the data.
Adipic Acid, MW = 146: Trans-cinnamic acid, MW=148HO2CCH2CH2CH2CH2CO2H -CH=CH-COOH
Citric Acid, MW = 192: Oxalic acid, MW = 90HO2C-CH2-C(OH)-CH2-CO2H HO2C—CO2H CO2H
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EW from Experiment Data
• EW = Mass (g) of acid providing 1 mol H+
or neutralizing 1 mol OH-.
Determine the equivalent weight of an unidentifiedcarboxylic acid by titration
EW = mass acid (g) moles of OH- neutralized
EW of Oxalic Acid (Part 4) EW of Oxalic Acid (Part 4)
Answer.______________________________________
Q. 10.0 mL of 1.0 M NaOH neutralizes 0.4502grams of an unknown acid. What is the equivalentweight of the acid?
Name Formula MW MP2-hydroxybenzoic acid acetate
COOH
OCOCH3
180 135
trans-cinnamic acid
CH CH COOH148 135-136
2-chlorobenzoic acid
Cl
COOH
157 140
cis-butenedioic (maleic) acid
H HHOOC COOH
116 139-140
Q. You titrate 0.175 g of an acid. 30.00 mL of 0.10 MNaOH neutralizes the sample.1) What is the acid’s EW based on the data?2) Identify the acid from the list below.
Q. You titrate 0.175 g of an acid. 30.00 mL of 0.10 MNaOH neutralizes the sample.1) What is the acid’s EW based on the data?2) Identify the acid from the list below.
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Equivalent weight determination.
mol OH- = V(L) x M NaOH
= ______________
1) Determine mol of NaOH the acid has neutralized.
Fact: The acid mass neutralized 30.00 mL of 0.10 M NaOH
Equivalent Weight determination.
X g acid 1 mol OH-
Known: 0.175 g = ____mol OH-
X = _______ g
2) Determine the mass of acid that wouldneutralize one mol of hydroxide ions.
Name Formula MW MP2-hydroxybenzoic acid acetate
COOH
OCOCH3
180 135
trans-cinnamic acid
CH CH COOH148 135-136
2-chlorobenzoic acid
Cl
COOH
157 140
cis-butenedioic (maleic) acid
H HHOOC COOH
116 139-140
Q. What is the identity of the acid?Q. What is the identity of the acid?
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