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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)

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

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

Titration (Parts 3)Titration (Parts 3)

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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

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

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

58

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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

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

• 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 = _____________?73

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. Compounds # 2 and # 4.

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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

Let X = # ionizable protons.EW = 72.50 = MW/X = 150/X X= ~ 2

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 from Experiment Data (Part 5)

Determine the EW of an acid by titration

EW of Oxalic Acid (Part 4) EW of Oxalic Acid (Part 4)

Answer.Fact: 0.4502 g neutralized 10.0 mmol of NaOH.

Q. 10.0 mL of 1.0 M NaOH neutralizes 0.4502grams of an unknown acid. What is the equivalentweight of the acid?

The mass of acid needed to neutralize 1 mol = 45.02g = EW

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.

Equivalent weight determination.

mol OH- = V(L) x M NaOH

= 0.0300L x 0.10 mol L = 3.0 x 10-3 mol

1) Determine mol of NaOH the acid has neutralized.

Fact: The acid mass neutralized 30.00 mL of 0.10 M NaOH

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Equivalent Weight determination.

X g acid 1 mol OH-

Known: 0.175 g = 0.0030 mol OH-

X = 58 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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Questions?Contact nkerner@umich.edu