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‘Why’ said the Dodo, ‘the best way to explain it is to do it.’

Alice in Wonderland Lewis Carroll

WHY

LABORATORY

?

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CHE CHE 133133A brief reviewA brief review

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THE EXERCISESTHE EXERCISES

LABORATORY MEASUREMENTLengths, Weights, Volumes,

Density

HOUSEHOLD "CHEMICALS"Food Dyes - Spectroscopy

Food Dyes – Chromatography Alum – Synthesis

Household Materials - Analysis Vanillyl Alcohol – SynthesisFruit Juices – Acid Content

Vinegar – Acid ContentBaking Soda - GasometryBaking Soda - Gravimetry

OH

OCH3

OC

H

Absorbance vs Wavelength

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength (nm)

Abso

rban

ce

NaHCO3

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THE HARDWARETHE HARDWARE

Pipet & SyringeBuret

Beakers, Cylinders, FlasksBunsen Burner

Hot PlateGas Syringe

Melting Point Apparatus Analytical BalanceTop Loading Balance

Visible/UV SpectrophotometerpH Meter

Infrared Spectrometer

Safety Goggles

xx.xxxx

xx.xx

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THE TECHNIQUESTHE TECHNIQUES

CHEMICAL ANALYSISVolumetric Techniques StandardizationWeighing (by difference) Gravimetric Analysis Flame Tests SpectrophotometryGas Collection and Measurement Melting PointsQualitative Infrared Spectroscopy

CHEMICAL SEPARATIONUse solubility for separation Paper ChromatographyGravity and Vacuum Filtration

CHEMICAL SYNTHESISAlum Vanillyl Alcohol

ANALYSIS OF EXPERIMENTAL DATAMeasures of accuracy and precisionSignificant Figures Tabulation and Graphing of Data

Prep’n of SolutionsQuantitative DilutionSolution Transfer Titration

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• H2O

• Food Dyes – B1, B2, G3, Y5, Y6, R3, R40, Isopropyl Alcohol, Salt Water

• Al, KOH, H2SO4, KAl(SO4)2·12H2O, KAl(OH)4, Al(OH)3

• Vanillyl Alcohol, Vanillin, NaBH4, NaOH, HCl

• Na2CO3, Urea, Ascorbic Acid, Borax, Na2S2O3, KHTartrate, CaCO3, Aspirin, Citric Acid, Ammonia,

Acetic Acid (vinegar), I2

• NaOH, Citric Acid, Phosphoric Acid, Acetic Acid, KHPhthalate, other naturally occurring acids

• NaHCO3, HCl, NaCl, CO2

THE “CHEMICALS”THE “CHEMICALS”

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• Stoichiometry*Stoichiometry*

• Beer’s Law A = A = εε b c b c

• Capillary Action - Qualitative

• Devising Synthetic Pathways

• Ideal Gas Law – (non-Ideality) PV= nRT PV= nRT

• Henry’s Law ssii = k P = k Pii

• Vibration Frequency νν = (1/2 = (1/2ππ)(k/)(k/μμ))½½

THE PRINCIPLES, LAWS & RULES OF THE PRINCIPLES, LAWS & RULES OF THUMBTHUMB

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On a LINEAR SCALELINEAR SCALE, human eye is capable of estimating the location of a mark lying between two smallest

divisions to the nearest 1/5 th of a division1/5 th of a division

* Balancing Chemical Equations – mole relationships

• Percent Transmittance %T = 100 I%T = 100 Itt / I / I00

• Absorbance A = log (IA = log (I0 0 / I/ Itt) ) A = 2.0000 – log (%T)

• Absorptivity is the εε in Beer’s Law A = A = εε b c b c

• Concentration c = amount / c = amount / volume volume

E.g., mol/L, mmol/mL, lbs/ft3, etc.

• Analytical Wavelength - λλ at which Absorbance is a at which Absorbance is a maximummaximum

• Retention Factor RRff = d = dspotspot / d / dsolvsolv

• Percent Yield %Y = act yield / %Y = act yield / stoich yieldstoich yield

• pH pH = - log [ HpH = - log [ H++ ] ]

• Acid Ionization Constant KKaa = [ H = [ H++ ][ A ][ A-- ]/[ HA ] ]/[ HA ]

• pKa pKpKaa = - log K = - log Kaa

DEFINITIONSDEFINITIONS

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The Final The Final QuizQuizPart 1 – Details - 50%

Part 2 – Concepts – 50%

Acids in juice

Acid in vinegarGravimetry

Gasometry

Above

+Laboratory MeasurementFood Dyes - Spectroscopy

Food Dyes – ChromatographySynthesis of Alum,

Household Materials - Analysis Vanillyl Alcohol - Synthesis 10

2 Parts2 Parts

100 points – 30 100 points – 30 minmin

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Acids in beverages

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HOW DOES THE STRENGTH OF AN ACID AFFECT HOW DOES THE STRENGTH OF AN ACID AFFECT ITS TITRATION CURVEITS TITRATION CURVE

pH at equivalence point changes

with pKa

pH

Volume of added NaOH13

1.) Determined the TOTAL AMOUNT OF ACID in a measured sample of the beverage by titrating the acid(s) with NaOH of known concentration.

The NaOH reacted with ALL OF THE ACID*, dissociated, or notdissociated, or not.

* We did not detect any acids with pKa’s > 9, - the pH at which phenolphthalein signals its end

point

In the exercise we made two measurements:

This told us the TOTAL of the DISSOCIATED + UNDISSOCIATED

ACID in the beverage.

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2. Measured pH of a beverage to determine the actual H+ concentration of the beverage using a pH METER – (electronic device designed to measure the hydrogen ion concentration in aqueous solutions)This told us the CONCENTRATION OF

DISSOCIATED H+ in the beverage,

[ H+ ] = 10-pH

pH = -log [ H+]

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Acid in vinegar

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PROCEDURPROCEDUREE

A. STANDARDIZATION Prepared solution of known concentration of primary standard, KHP*

• Weighed out sample BY DIFFERENCE• Brought to total volume in VOLUMETRIC VOLUMETRIC FLASK**FLASK**• Calculate concentration of KHP = wt KHP mg/(204.2 mg/mmol x VH2O

mL) = 3087.0 / (204.2 x 250.0) = 0.06047 M KHP

* potassium hydrogen phthalate

O

O

OH

O-K

or, = 3.0870 g / (204.2 g/mol x 0.2500

L)

~ 3g

250.0 mL

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PROCEDURPROCEDUREE Determine concentration of stock NaOH

Solution ( NominallyNominally 0.1 M )

with

(Delivered from

buret 1buret 1 )

measured volumes of NaOH Solution

(unknownunknown concentration)

Titrate

measured volumes of standard KHP solution (knownknown concentration)

(Delivered from

buret 2buret 2 )

KHPKHP NaONaOHH

18K+ + HP- + OH- → K+ + P= +

H2O

CALCULATIONS – NaOH STANDARDIZATIONMolarity of KHP Solution: 0.06047 M

KHP buret reading, final 37.44 mL 38.77 KHP buret reading, initial 3.68 mL 4.73Volume of KHP titrated 33.76 mL 34.04

NaOH buret reading, final 28.73 mL 31.83NaOH buret reading, initial 4.52 mL 7.88Volume of NaOH used 24.21 mL 23.95

mmol of KHP titrated 33.76 mL X 0.06047 M = 2.042 mmol 2.202mmol of NaOH used 2.042 mmol 2.202

Molarity of NaOH 2.042 mmol / 24.21mL = 0.08435 M 0.08526 M

Stoichiometry is 1 to 1

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CALCULATIONS - UNKNOWN

Volume of Unknown 5.00 mL 5.00 5.00

Concentration of NaOH solution 0.08435 M

NaOH buret, final 22.47 mL 21.16 23.72 NaOH buret, initial 3.15 mL 2.37 4.22 Volume NaOH used 19.32 mL 18.79 19.50

mmol of NaOH used19.32 * 0.08435 = 1.630 mmol 1.585 1.645

mmol of Acetic Acid titrated = 1.630 mmol 1.585 1.645

Acetic Acid Concentration1.646 / 5.00 = = 0.326 M 0.317 0.329

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From Standardizati

on

3 Sig Figs

Stoichiometry is 1 to 1

20HOAc + OH- → OAc- + H2O

Gasometric NaHCO3

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NaHCO3 (s) + H+ Na+ (aq) + H2O (l) + CO2 (g)

Ideal Gas Law Henry’s Law Vapor Pressure

Gasometric Determination of NaHCOGasometric Determination of NaHCO3 3 in a in a MixtureMixture

Cl- Cl-

PH2O,T, vI, nair nCO2

g

nnCO2CO2ss

P P PH2O,T, vF, nair,

nCO2g = (P – PH2O) VCO2 / RT

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Calculations Calculations

Weight of Sample 0.2147 gVolume of gaseous CO2 v 45.7 mLPressure, P = 752 mm Hg = 0.989 atmTemperature, T = 23oC = 296 KPH2O@ 23oC - 21 mm Hg 0.028 atm

mmol CO2 (gas) = (P - PH2O)v / RT1.81 mmolmmol CO2 (liquid) (Henry’s Law) ??????

From TableCalculatedMeasured

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To calculate the Henry’s Law correction, we need the volume of the System. Suppose it is 100.0 mL

That makes the initial volume,VI = 100.0 -10.0 + 5.0 = 95.0 mL

PCO2 = nCO2g RT / vF = ( P - PH2O )( 1 – vI / vF)

= ( 0.989 – 0.028)( 1 – 95.0 / 140.7) = 0.312 atm

SCO2 = 3.2 X 10-2 mmol/mL-atm X 0.312 atm

= 10.0 mL X 0.010 mmol/mL

and the final volume,VF = 100.0 -10.0 + 50.7= 140.7 mL

Vsys = 100.0 mLSyringe:Initial = 5.0 mLFinal = 50.7 mL

SCO2 = kH X PCO2

nnCO2CO2s s = Volume X Concentration

= 0.010 M

= 0.10 mmol

Volume of HCl

ConcentrationConcentration

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AmountAmount

Calculations Calculations

Weight of Sample 0.2147 gVolume of gaseous CO2 v 45.7 mLPressure, P = 752 mm Hg = 0.989 atmTemperature, T = 23oC = 296 KPH2O@ 23oC (from Table) 21 mm Hg 0.028 atm

mmol CO2 (gas) = (P - PH2O)v / RT1.81 mmolmmol CO2 (liquid) (Henry’s Law) 0.10 mmol

Tot CO2 1.91 mmolmmol NaHCO3 (from stoichiometry) 1.91 mmolWeight of NaHCO3 1.91 X 84.0 0.160 g

% NaHCO3 = 100 X 0.160 / 0.2147 = 74.5 %

Calculated

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CO2 = kH X PO2 = 1.3 X 10-3 M/atm X 0.20 atm = 2.6 X 10-4 M

mmol O2 = 2.6 X 10-4 M X 400 mL = 0.10 mmol in water

A simple example of Henry’s LawA simple example of Henry’s Law

M = mmol/mL

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nO2 = PO2 v / RT = 0.20 X 50 / 0.0821 X 283 = 0.43mmol in gas

mg Omg O22 = (0.43 + 0.10 ) mmol X 32 mg/mmol = = (0.43 + 0.10 ) mmol X 32 mg/mmol = 17 mg17 mg

Dissolved Oxygen in Water:

The Henry’s Law constant, kH, for Oxygen in water at 10 oC is 1.3 X 10-3 M/atm. A sealed water bottle has a total volume of 450 mL and is filled with 400 mL of water. What is the total mg of O2 in the sealed bottle? P = 1.0 atm ; T = 10 oC; R = 0.0821 mL-atm/mmol-K; PH2O = .012 atm at 10 oC

(Air is about 20% oxygen, so PO2 ~ 0.20 atm.)

Gravimetric NaHCO3

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2 NaHCO3 (s) Na2CO3 (s) + H2O (g) + CO2

(g)

Thermal Decomposition Constant Weight

Gravimetric Determination of NaHCOGravimetric Determination of NaHCO33 in a in a MixtureMixture

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This Part of the Exercise is, again This Part of the Exercise is, again ConceptuallyConceptually Simple.Simple.

1.Weigh Sample,

2. Decompose the sample by heating

3. Weigh product to get weight of CO2 & H2O lostlost weight loss = wCO2 + wH2O

= nCO2 * 44.01Molar

Mass of CO2

Molar Mass

of H2O

+ nH2O * 18.02

2 NaHCO3 (s) Na2CO3 (s) + H2O (g)+ CO2 (g)

wSample.

weight = mol X Mol Mass

+ NaCl (s)

+ NaCl (s)

2 NaHCO3 (s)

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weight loss

4. Get moles of CO2 , H2O and NaHCO3 lost

NaHCO3 (s) ½ Na2CO3 (s) + ½ H2O (g) + ½ CO2 (g) nCO2 = nH2O = ½ nNaHCO3

= ½ nNaHCO3 * ( 44.01 + 18.02 ) or, nNaHCO3

=5. wNaHCO3

=6. Compute Percent Composition of

Sample

PctNaHCO3 = 100 * wNaHCO3 / wSample

Molar Mass of NaHCO3

(= nCO2 * 44.01

+ nH2O * 18.02 )

so, weight loss

2 * ( weight loss ) / 62.03

nNaHCO3 * 84.01 g / mol

2 ½

½

½

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wNaHCO3 =

PctNaHCO3 = 100 * wNaHCO3 / wSample

nNaHCO3 * 84.01 g / mol2 * ( weight loss

) 62.03

X 84.01

= 2.709 * ( weight loss )

= 270.9 * ( weight loss ) / wSample

How is Pct NaHCOHow is Pct NaHCO33 related to the weight related to the weight loss?loss?

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wNaHCO3 = ( weight loss ) / 0.3691

nNaHCO3 =

wNaHCO3 =

2 * ( weight loss )

62.03

Showed that:

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wNaHCO3 = ( weight loss ) / 0.3691

How much weight would 1.000 g of How much weight would 1.000 g of purepure NaHCONaHCO33 lose? lose?

wNaHCO3 = 1 g

1 g = ( weight loss ) / 0.3691

weight loss = 0.3691 g

PctNaHCO3 = 100 * wNaHCO3 / wSample

270.9 * ( weight loss ) / wSample = 270.9 * 0.3691/

1.000 = 100.0 %

Wt of crucible + sample 16.0755 g

Wt of crucible 14.9842 g

Wt of sample

Wt of evap dish + residue –after heat 15.8689 g

Wt of residue [ 15.8689 – 14.9842 ]

Wt lossWt loss [ 1.0913 – 0.8847 ]

Wt NaHCO3 [ 0.2066 / 0.3691 ]

% NaHCO3 [100 X 0.5597 / 1.0913 ]

DATA SHEETDATA SHEET

0.8847 g

0.2066 g

0.5597 g

51.29 %

1.0913 g

Wt loss per gram

of NaHCO3

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The Final The Final QuizQuizPart 1 - Details

Part 2 - Concepts

Acids in Juice Acid in Vinegar

Gravimetry

Gasometry

Laboratory MeasurementFood Dyes - Spectroscopy

Food Dyes – ChromatographySynthesis of Alum,

Household Materials - Analysis Vanillyl Alcohol - Synthesis

34

Concepts:Concepts:Measurement Uncertainty Linear Mass/Weight Volume Density

Deliver/Contain Meniscus Homogeneity

Accuracy Precision Average Significant Figures Average Deviation Percent Error Error Propagation

Laboratory MeasurementLaboratory Measurement

L = 9.00 L = 10.0 L = 11.0

VOLUME 729 1000* 1331*

Diff from L=10 (cm) 271 0 331

Diff from L=10 (%) -27.1% 0% +33.1% 35

You also explored the intrinsic errors and precision limitations of a number of

common laboratory devices

On a LINEAR SCALELINEAR SCALE, human eye is capable of estimating the location of a mark lying between two smallest

divisions to the nearest 1/5 th of a division1/5 th of a division

RULE OF THUMB:

the importance of recognizing both limitations and capabilities of

measurement devices and sig figs as a representation.

and

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37

Analytical Balance YY.XXXX

Top Loading Balance Y.XX

50 mL Graduated Cylinder YY.X

Buret YY.XX

AVERAGE: M1 + M2 + …. + Mn

n

PERCENT DEVIATION:

100 X AVG DEV AVG

AVERAGE DEVIATION:

|M1 – AVG| + |M2 – AVG| + … + |Mn – AVG| n

Simple Statistical MeasuresSimple Statistical Measures

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Concepts: Concentration Transmittance Absorbance Analytical Wavelength Beer’s Law BlankSpectrum Absorptivity

Spectroscopy of Food DyesSpectroscopy of Food Dyes

A = ε b c

Absorbance vs Wavelength

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

350

380

410

440

470

500

530

560

590

620

650

680

710

740

Wavelength (nm)

Ab

so

rba

nc

e

This wavelength is called the ANALYTICAL WAVELENGTH

Absorbance vs ConcentrationRed Dye #2 at 470 nm

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30 35 40 45 50Concentration (mg/L)

Ab

sorb

ance

vis/uv = electronic

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Concepts: chromatography mobile phase migration rate stationary phase solvent front resolutionretention factor capillary action solvents

Chromatography of Food DyesChromatography of Food Dyes

Origin

Solvent Front

dsolvent

dspot

dspot

Rf = -------------dsolvent

Some solvents are better than others 40

Al(OH)4- + H+ H2O + Al(OH)3(s)

Al(OH)3(s) + 3 H+ + 3 H2O Al(H2O)6

3+

M(I)T(III) (SO4)2.12 H2O

Alum SynthesisAlum Synthesis

2 Al (s) + 2 OH- + 6 H2O 2 Al(OH)4- + 3H2

(g)

Synthesis Product Starting MaterialYield Percent YieldStoichiometryWater of crystallizationTemperature dependence of solubility 41

CaCO3(s) + 2 H+ Ca2+ + H2O + CO2(g)CO3

= (aq) + 2 H+ H2O + CO2(g)2 S2O3

= + I2 2I- + S4O6=

C6H8O6 + I2 2I- + C6H6O6 + 2 H+

sodium thiosulfate (hypo)vitamin C (ascorbic acid)

Identification of Household Identification of Household ChemicalsChemicals

reducing agents

Carbonates react with acids to give off CO2 (g)

react with I2 to give I- 42

Reduction of vanillin to vanillyl alcohol using

NaBH4

43

OH

OCH3

HC

O

OH

OCH3

HOC

HH

+ BH4- + 4 H2O

+ H3BO3 + OH-

4 4

vanillin

sodium borohydride

vanillyl alcohol

Theoretical yield Percent yield Reduction /H2 StoichiometryInfrared absorptions Organic functional groups

Net Effect:

Addition of 2 H atoms

aldehyde

44

O-H

-H C-H3 HC=O CC

VanillinVanillin IR Spectrum 1500 cm-1 – 4000 cm-1

H

H

H

OH

OCH3

HOC

HH

X45

IR = vibrations

Some Common Some Common CalculationsCalculations

Dilutions:

Conc1 * Volume1 = Conc2 * Volume2

Molarity1 * Volume1 = Molarity2 * Volume2

Solutions: mmols = Molarity * Volume (mL)

Solids: mols = Weight / Molar Mass

Gases: Pressurei * Volume = molsi * RT

Pct Yield = 100 x Actual Yield/Theoretical Yield

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Some Possible AnswersSome Possible Answers

c

3.1 X 10 -

5

F

35% bNeverAll o

f the

above

Yesc

25oC T

Blue

a

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If you are continuing in CHE 134

Keep your:Safety GogglesLockTowel ?

The same Laboratory notebook

can be used next semester.

48

ACADEMIC CALENDAR - SPRING 2013ACADEMIC CALENDAR - SPRING 2013

Mo Tu We Th Fr

Jan 28 29 30 31 1

4 5 6 7 8

CHE 134 LABS WILL NOT MEET during the first week of class (1/23 – 1/27).

Students who fail to attend second week LAB meetings will be de-registered (2/4 –

2/7)

lecture

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Monday Lecture does NOT meet on Monday Lecture does NOT meet on 1/281/28

Friday lecture DOES meet on 2/1Friday lecture DOES meet on 2/1

IF CLASSES ARE CANCELEDIF CLASSES ARE CANCELED

CHECK THE

COURSE WEBSITE

orBlackboard

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Please complete the course

evaluation for both the lecture and

laboratory components of the

course.

We’ll see most of you again for

more exercises in

62.00 days

= 1,488 hrs

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