CHP3 Lab Lab Instructions

CHP3 Lab

Lab Instructions

Polmerization of methylmethacrylateCHP3_8ChromatographyCHP3_7Potentiometric determination of chlorideCHP3_6Biotechnological ethanol synthesisCHP3_5Electrical conductivity of electrolyte solutionsCHP3_4Synthesis of benzoic acid (ester hydrolysis)CHP3_3Synthesis of ethyl benzoate (ester synthesis)CHP3_2Fractional distillationCHP3_1Technical reports Intro

Prof. Dr.-Ing. Brigitte HaaseDipl.-Ing. Peter Iwaneczko

Angewandte Chemie

Hochschule Bremerhaven – An der Karlstadt 8 – D-27568 Bremerhaven

page 1 cover 26.03.2008

Technical Reports

Technical personnel write technical reports fortwo primary purposes. Technical reports areused to communicate information to customers,colleagues and managers, and they are usedto document the equipment and proceduresused in testing or research and the resultsobtained so that the work can be repeated ifnecessary or built upon. Lab reports, bachelorand master theses as well as PHD theses fallin this group, too. The content and style oftechnical reports vary widely depending on theprimary purpose and the audience. Manycompanies and organizations have developedtheir own standard format. The sections gener-ally included in technical reports are shown tothe right.

Qualities of Good Technical Reports Regardless of the specific format used, all quality technical reports will posses the followingqualities:

AccuracyGreat care should be taken to ensure that the information is presented accurately. Make surevalues are transferred correctly into the report and calculations are done properly. Since manypeople proof read right over their own typographical errors, it is often best to have another personproofread the report. Mistakes may cause the reader to doubt other points of the report and reflecton the professionalism of the author.

ObjectivityData must be evaluated honestly and without bias. Conclusions should be drawn solely from thefacts presented. Opinions and conjecture should be clearly identified if included at all. Deficienciesin the testing or the results should be noted. Readers should be informed of all assumptions andprobable sources of errors if encountered.

ClarityThe author should work to convey an exact meaning to the reader. The text must be clear andunambiguous, mathematical symbols must be fully defined, and the figures and tables must beeasily understood. Clarity must be met from the readers' point of view. Don’t assume that readersare familiar with previous work or previous reports. When photographs are included in a report, ascale or some object of standard size should be included in the photograph to help your readersjudge the size of the objects shown. Simply stating the magnification of a photograph can causeuncertainty since the size of photographs often change in reproduction.

ConcisenessMost people are fairly busy and will not want to spend any more time than necessary reading areport. Therefore, technical reports should be concisely written. Include all the details needed tofully document and explain the work but keep it as brief as possible. Conciseness is especiallyimportant in the abstract and conclusion sections.

page 2

Source: http://www.ndt-ed.org/GeneralResources/Report/TechReport.htm

Figure 1 General structure of a technical report

Continuity Reports should be organized in a logical manner so that it is easy for the reader to follow. It is oftenhelpful to start with an outline of the paper, making good use of headings. The same three stepapproach for developing an effective presentation can be used to develop an effective report:

1) Introduce the subject matter (tell readers what they will be reading about),2) Provide the detailed information (tell them what you want them to know),3) Summarize the results and conclusions (re-tell them the main points).

Make sure that information is included in the appropriate section of the report. For example, don’tadd new information about the procedure followed in the discussion section. Information about theprocedure belongs in the procedure section. The discussion section should focus on explaining theresults, highlighting significant findings, discussing problems with the data and noting possiblesources of error, etc. Be sure not to introduce any new information in the conclusion sections. Theconclusion section should simple state the conclusion drawn from the work.

Writing Style A relatively formal writing style should be used when composing technical reports. The personalstyle of the writer should be secondary to the clear and objective communication of information.Writers should, however, strive to make their reports interesting and enjoyable to read.

page 3

Source: http://www.ndt-ed.org/GeneralResources/Report/TechReport.htm

General structure

1.1. TheoryFundamentals - see literature nad textbooks

Theoretical background - especially laws and equations used for the evaluation of results. Formulasand abbrevations must be explained.

Example:

; (1)E(Ag+/Ag) = E0 − RTzF ln

a(Ag)a(Ag+) ;E0 = 0.800V

E/V: electrode potential

E 0/V: standard reduction potential

R = 8.3144 J K-1 mol-1: gas constant

T/K: temperature

z: number of exchanged electrons, according to reduction eqn.

F = 96485 C mol-1: Faraday constant

a(i): activity of component i

Form and style: Figures and tables must have a number, a footing and must be cited and explained inthe text above/below.

Example:

Figure 1Titration curve of tap water

Table 1 Salt content of bakery products

1.2. Experimental

1.1 Experimental set-upApparatus, instruments, chemicals, table with individual experiamental parameters if necessary.Reason: Repeatability of the experiment by others.

1.2 ProcedureDescription of experimental procedure, according to the rules referring to style, vocabulary etc.!

1.3. ResultsTable of experimental results, graphs of direct experimental results, calulation of results if necessary(preferably within the table)Discussion

Further calculations, evaluations and graphs.

Includes discussion of plausibility, discussion of errors, reliability. If the results differ from the expectedvalues, the deviations must be explained.

CHP3 Lab Introduction page 1 of 2

page 1 Intro 2: Style details 26.03.2008

1.1 Additional questionsAnswers of questions, see lab instructions!

1.4. ConclusionsShort presentation (three to five sentences) of the general outcome.

1.5. Literature and referencesList of textbooks, web sites etc.

CHP3 Lab Introduction page 1 of 2

page 2 Intro 2: Style details 26.03.2008

Significant Figures (Digits)

When reporting values that were the result of a measurement or calculated using measuredvalues, it is important to have a way to indicated the certainty of the measurement. This isaccomplished through the use of significant figures. Significant figures are the digits in a value thatare known with some degree of confidence. As the number of significant figures increases, themore certain the measurement. As precision of a measurement increases, so does the number ofsignificant figures. Consider the weight measurements made using the following threeinstruments. Notice that the number of significant digits increase as the measured value gets moreprecise and the range of uncertainty gets smaller.

Keywords:

v Instrument

v Measured Value

v Precision of Measurement

v Minimum Amount of Uncertainty in the Measurement

v Significant Figures of Measured Value

Postage Scale

3g 1g +/- 0.5g ===> 1 sF

Two-pan balance

2.53g 0.01g +/- 0.005g ===> 3sF

Analytical balance 2.531g 0.001g +/- 0.0005g ===> 4sF There are conventions that must be followed for expressing numbers so that their significantfigures are properly indicated. These conventions are:

v All non zero digits are significant.

v 549 has three significant figures

v 1.892 has four significant figures

v Zeros between non zero digits are significant.

4023 has four significant figures50014 has five significant figures

v Zeros to the left of the first non zero digit are not significant.

0.000034 has only two significant figures. (This is more easily seen if it is written as3.4x10-5) 0.001111 has four significant figures.

Seite 3

Source: http://www.ndt-ed.org/GeneralResources/SigFigs/SigFigs.htm

Trailing zeros (the right most zeros) are significant when there is a decimal point in thenumber. For this reason it is important to give consideration to when a decimal point is used andto keep the trailing zeros to indicate the actual number of significant figures.

v 400. has three significant figures

v 2.00 has three significant figures

v 0.050 has two significant figures

Trailing zeros are not significant in numbers without decimal points.

v 470000 has two significant figures 400 or 4x102 indicates only one significant figure. (To indicate that the trailing zeros aresignificant a decimal point must be added. 400. has three significant digits and is written as4.00x102 in scientific notation.)

v Exact numbers have an infinite number of significant digits but they are generally not reported.

v Defined numbers also have an infinite number of significant digits.

If you count 2 pencils, then the number of pencils is 2.000...

The number of centimeters per inch (2.54) has an infinite number of significant digits, asdoes the speed of light (299792458 m/s).

Maintaining Significant Digits in CalculationsOnce the number of significant figures various values have been determined, the issue thenbecomes dealing with significant figures when these values are used in calculations. Whencombining values with different degrees of precision, the precision of the final answer can be nogreater than the least precise measurement. However, it is a good idea to keep one more digitthan is significant during the calculation to reduce rounding errors. In the end, however, the answermust be expressed with the proper number of significant figures.

Addition and SubtractionWhen adding and subtracting, round the final result to have the same precision (same number ofdecimal places) as the least precise initial value, regardless of the significant figures of any oneterm. For example,

98.112 + 2.3 = 100.412 but this value must be rounded to 100.4 (the precision of the least preciseterm).

Multiplication, Division, and RootsWhen multiplying, dividing, or taking roots, the result should have the same number of significantfigures as the least precise number in the calculation. For example,

(3.69) (2.3059) = 8.5088, which should be rounded to 8.51 (three significant figures like 3.69).

Logarithms and AntilogithmsWhen calculating the logarithm of a number, retain in the mantissa (the number to the right of thedecimal point in the logarithm) the same number of significant figures as there are in the numberwhose logarithm is being found. For example,

log(3.000x104) = 4.477121, which should be rounded to 4.4771

log(3x104) = 4.477121, but this value should be rounded to 4.5

When calculating the antilogarithm of a number, the resulting value should have the same numberof significant figures as the mantissa in the logarithm. For example,

Seite 4


antilog(0.301) = 1.9998, which should be rounded to 2.00,

antilog(0.30) = 1.9998, which should be rounded to 2.0

Multiple Mathematical Operations If a calculation involves a combination of mathematical operations, perform the calculation usingmore figures than will be significant to arrive at a value. Then, go back and look at the individualsteps of the calculation and determine how many significant figures would carry through to the finalresult based on the above conventions. For example,

X = ((5.254+0.0016)/34.6) - 2.231x10-3

Calculate the value of X using more digits than will be significant. In this caseX = 0.1496649538

Then, go back and look at each piece of the equation to determine the significant figures.

5.254 + 0.0016 = 5.256 (since the sum is limited to the thousandths place by 5.254);

5.256 / 34.6 = 0.152 (since the quotient is limited to 3 significant figures by 34.6);

0.152 - 0.002231 = 0.149 (since the difference is limited to the thousandths place by 0.152).

The value initially obtained for X (0.1496649538) should be rounded to have 3 significant digits.Therefore, the final answer is 0.150 or 1.50x10-1

The Rules of RoundingWhen a value contains too many significant figures, it must be rounded off. There are twomethods that are commonly used to minimise the error introduced into a value to rounding.

Method 1: This method involves underestimating the value when rounding the five digits 0, 1, 2, 3,and 4, and overestimating the value when rounding the five digits 5, 6, 7, 8, and 9. With thisapproach, if the value of the digit(s) to the right of the last significant figure is smaller than 5, dropthis digit and leave the remaining number unchanged. Thus, 2.794 becomes 2.79. If the value ofthe digit(s) to the right of the last significant digit is 5 or larger, drop this digit and add 1 to thepreceding digit. Thus, 2.795 becomes 2.80. This is the common method.

Method 2: This method takes into account that zero doesn't really require rounding and whenrounding 5, this value is exactly centered between the underestimated value if it is rounded downand the overestimated value if it is rounded up. Therefore, five should be rounded up half of thetime and down half of the time. Since it would difficult to keep track of this when performingnumerous measurements or calculations, 5 is rounded down when the preceding significant digit iseven and 5 is rounded down when the preceding significant digit is odd. Values less than 5 arerounded down and values greater than 5 are rounded up. For example, 2.785 would be roundeddown to 2.78 and 2.775 would be rounded up to 2.78. This method is not generally applied.

Seite 5


Accuracy, Error, Precision, and Uncertainty

IntroductionAll measurements of physical quantities are subject to uncertainties in the measurements. Variabil-ity in the results of repeated measurements arises because variables that can affect the measure-ment result are impossible to hold constant. Even if the "circumstances," could be preciselycontrolled, the result would still have an error associated with it. This is because the scale wasmanufactured with a certain level of quality, it is often difficult to read the scale perfectly, fractionalestimations between scale marking may be made and etc. Of course, steps can be taken to limitthe amount of uncertainty but it is always there.

In order to interpret data correctly and draw validconclusions the uncertainty must be indicatedand dealt with properly. For the result of ameasurement to have clear meaning, the valuecannot consist of the measured value alone. Anindication of how precise and accurate the resultis must also be included. Thus, the result of anyphysical measurement has two essential compo-nents: (1) A numerical value (in a specifiedsystem of units) giving the best estimate possibleof the quantity measured, and (2) the degree ofuncertainty associated with this estimatedvalue. Uncertainty is a parameter characterizingthe range of values within which the value of themeasurand can be said to lie within a specifiedlevel of confidence. For example, a measure-ment of the width of a table might yield a resultsuch as 95.3 +/- 0.1 cm. This result is basically communicating that the person making themeasurement believe the value to be closest to 95.3 cm but it could have been 95.2 or 95.4cm. The uncertainty is a quantitative indication of the quality of the result. It gives an answer tothe question, "how well does the result represent the value of the quantity being measured?"

The full formal process of determining the uncertainty of a measurement is an extensive processinvolving identifying all of the major process and environmental variables and evaluating theireffect on the measurement. This process is beyond the scope of this material but is detailed in theISO Guide to the Expression of Uncertainty in Measurement (GUM) and the corresponding Ameri-can National Standard ANSI/NCSL Z540-2. However, there are measures for estimating uncer-tainty, such as standard deviation, that are based entirely on the analysis of experimental datawhen all of the major sources of variability were sampled in the collection of the data set.

The first step in communicating the results of a measurement or group of measurements is tounderstand the terminology related to measurement quality. It can be confusing, which is partlydue to some of the terminology having subtle differences and partly due to the terminology beingused wrongly and inconsistently. For example, the term "accuracy" is often used when "trueness"should be used. Using the proper terminology is key to ensuring that results are properlycommunicated.

Seite 6

Source: http://www.ndt-ed.org/GeneralResources/ErrorAnalysis/UncertaintyTerms.htm

Figure 1Trueness, precision, bias and error

True ValueSince the true value cannot be absolutely determined, in practice an accepted reference value isused. The accepted reference value is usually established by repeatedly measuring some NIST orISO traceable reference standard. This value is not the reference value that is found published ina reference book. Such reference values are not "right" answers; they are measurements thathave errors associated with them as well and may not be totally representative of the specificsample being measured.

Accuracy and ErrorAccuracy is the closeness of agreement between a measured value and the true value. Error isthe difference between a measurement and the true value of the measurand (the quantity beingmeasured). Error does not include mistakes. Values that result from reading the wrong value ormaking some other mistake should be explained and excluded from the data set. Error is whatcauses values to differ when a measurement is repeated and none of the results can be preferredover the others. Although it is not possible to completely eliminate error in a measurement, it canbe controlled and characterized. Often, more effort goes into determining the error or uncertaintyin a measurement than into performing the measurement itself.

The total error is usually a combination of systematic error and random error. Many times resultsare quoted with two errors. The first error quoted is usually the random error, and the second is thesystematic error. If only one error is quoted it is the combined error.

Systematic error tends to shift all measurements in a systematic way so that in the course of anumber of measurements the mean value is constantly displaced or varies in a predictableway. The causes may be known or unknown but should always be corrected for whenpresent. For instance, no instrument can ever be calibrated perfectly so when a group of measure-ments systematically differ from the value of a standard reference specimen, an adjustment in thevalues should be made. Systematic error can be corrected for only when the "true value" (such asthe value assigned to a calibration or reference specimen) is known.

Random error is a component of the total error which, in the course of a number of measurements,varies in an unpredictable way. It is not possible to correct for random error. Random errors canoccur for a variety of reasons such as:

v Lack of equipment sensitivity. An instrument may not be able to respond to or indicate achange in some quantity that is too small or the observer may not be able to discern thechange.

v Noise in the measurement. Noise is extraneous disturbances that are unpredictable orrandom and cannot be completely accounted for.

v Imprecise definition. It is difficult to exactly define the dimensions of a object. For example, itis difficult to determine the ends of a crack with measuring its length. Two people may likelypick two different starting and ending points.

Trueness and BiasTrueness is the closeness of agreement between the average value obtained from a large seriesof test results and an accepted true. The terminology is very similar to that used in accuracy buttrueness applies to the average value of a large number of measurements. Bias is the differencebetween the average value of the large series of measurements and the accepted true. Bias isequivalent to the total systematic error in the measurement and a correction to negate the system-atic error can be made by adjusting for the bias.

Precision, Repeatability and ReproducibilityPrecision is the closeness of agreement between independent measurements of a quantity underthe same conditions. It is a measure of how well a measurement can be made without reference to

Seite 7


a theoretical or true value. The number of divisions on the scale of the measuring device generallyaffects the consistency of repeated measurements and, therefore, the precision. Since precision isnot based on a true value there is no bias or systematic error in the value, but instead it dependsonly on the distribution of random errors. The precision of a measurement is usually indicated bythe uncertainty or fractional relative uncertainty of a value.

Repeatability is simply the precision determined under conditions where the same methods andequipment are used by the same operator to make measurements on identical specimens. Repro-ducibility is simply the precision determined under conditions where the same methods but differ-ent equipment are used by different operator to make measurements on identical specimens.

UncertaintyUncertainty is the component of a reported value that characterizes the range of values withinwhich the true value is asserted to lie. An uncertainty estimates should address error from allpossible effects (both systematic and random) and, therefore, usually is the most appropriatemeans of expressing the accuracy of results. This is consistent with ISO guidelines. However, inmany measurement situations the systematic error is not address and only random error isincluded in the uncertainty measurement. When only random error is included in the uncertaintyestimate, it is a reflection of the precision of the measurement.

SummaryError is the difference between the true value of the measurand and the measured value. The totalerror is a combination of both systematic error and random error. Trueness is the closeness ofagreement between the average value obtained from a large series of test results and theaccepted true. Trueness is largely affected by systematic error. Precision is the closeness ofagreement between independent measurements. Precession is largely affected by randomerror. Accuracy is an expression of the lack of error. Uncertainty characterizes the range ofvalues within which the true value is asserted to lie with some level of confidence.

References:1. Royal Society of Chemistry, Analytical Methods Committee Technical Brief, No. 13, September

2003. 2. ANSI/NCSL, Z540-2-1997, “U.S. Guide to the Expression of Uncertainty in Measurement”, 1st

ed., October 1997.Eurachem/CITAC, “Quantifying Uncertainty in Analytical Measurement”, 2nd edition, 2000.

3. NIST/SEMATECH e-Handbook of Statistical Methods, http://www.itl.nist.gov/div898/handbook/,2006

4. ISO 5725-1, “Accuracy (trueness and precision) of measurement methods and results – Part 1:General principlesand definitions”.

Seite 8


Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung

VersuchsdatumName, Vorname, Matrikelnr.Gruppe

CHP3L_01Fractional Distillation

1. Objectives and general procedureA model mixture from three hydrocarbons is separated by fractional distillation at con-stant temperature (variable pressure). The composition, i.e. purity, of the fractions isdetermined by their physical properties, and by IR spectroscopy.

1.1. Pre-lab preparationComposition of petroleum, fractional distillation, vapor pressure, Clausius-Clapeyronequation, vapor pressure vs. temperature diagram, enthalpy of vaporization, physico-chemical properties of hydrocarbons (volatility, refractive index, density), IRspectroscopy.

Literature:

1) All general chemistry textbooks

2) Atkins' Physical chemistry, any edition

Data for calculation

36.4 139.1 m-Xylene 35.8 101.4 1.4-Dioxane 36.8 144.4 o-Xylene26.6 34.5 Diethylether 40.7 100 Water 42.4 161.4 Cyclohexanol 33.5 110.6 Toluene30.1 80.7 Cyclohexane 30.0 76.7 Tetrachloromethane 29.7 61.3 Chloroform 35.1 115.2 Pyridine35.7 131.7 Chlorobenzene34.6 125.7 n-Octane39.7 82.6 t-Butanol 34.0 101.2 Nitromethane 41.7 100.0 2-Butanol48.8 211 Nitrobenzene43.8 117.8 1-Butanol32.8 79.6 Methylethylketone 36.4 156.1 Bromobenzene 35.4 64.7 Methanol 50.5 205.4 Benzyl alcohol 40.5 82.4Isopropanol 30.8 80.1 Benzene28.9 68.7 n-Hexane 184.4 Aniline 38.7 78.3 Ethanol 32.8 81.6 Acetonitrile 32.3 77.1 Ethyl acetate 38.8 202.3 Acetophenone 23.7 117.9 Acetic acid29.1 56.2 Acetone

vH/kJ mol-1bp. in oCSolvent vH/kJmol-1bp in oC Solvent

Table 1 Boiling points and molar enthalpies of vaporization of some organicsolvents

page 1 CHP3_1: Fractional distillation 26.03.2008

Clausius-Clapeyron equation: (Boiling point versus pressure and vice versa):

(1)lnp2 = lnp1 − vHR

1T2

− 1T1

1.2. EvaluationBalance of matter (Mass or volume balance): Balance of all fractions.

Composition: Compare all measuring results to those of the pure substances (asmeasured and/or literature). Use this information to complete the balance withresoect to the three hydrocarbons.

1.3. DiscussionDiscuss the fractions' purities and the efficiency of the separation. Estimate the com-position of each fraction. Discuss the measuring methods with respect to indentica-tion of the substances and quantification of the composition.

Figure 1 n-Hexane FTIR spectrum

Figure 2 Cyclohexane FTIR spectrum


Figure 3 Toluene FTIR spektrum

2. Experimental

2.1. Instruments and glasswareSemi-industrial-scale fractional distillation plant with temperature and pressure con-trol, water-jet vacuum pump.

Refractometer, volumetric flasks, IR spectrometer, analytical balance

2.2. Chemicals

3 different hydrocarbons (à 100 mL each), 10 mL of crude oil; ice-salt mixture forcooling.

2.3. Procedure Distillation

The distillation is perfomed in a half-technical vacuum distillation plant. The distillationflask is filled with the hydrocarbon mixture, the plant's cooling is activated and theheating is turned on. The reflux ratio is infinite (reflux valve completely closed) untilthe temperature at the top is constant at 70 °C, and the distillation column is station-ary (or in equilibrium). Afterwards, the reflux valve is opened and the distillationstarts. The condensate must be cooled additionally using the ice-salt mixture, other-wise it will partially vaporize again and contaminate other fraction samplers or frac-tions. The first fraction is distilled at atmospheric pressure, afterwards, the heating isremoved and the first fraction is collected from the fraction sampler.

The water-jet pump is switched on and the pressure for the second fraction is set. Asthere are 4 fraction samplers, up to 2 intermediate fractions can collected without set-ting back the process. All other fractions are distilled at variable pressure and con-stant still temperature (temperature at the top of the column) of app. 70°C.


Afterwards, the plant is set back by (1) removing the heating, letting cool down,(2) open external pressure valve to ambient pressure, (3) collect fractions and inter-mediates for measuring out and further analysis.

Analysis

1) Density

The densities of the pure standards, of the fractions and the intermediates aremeasured using an analytical balance and a volumetric pipette. You must workfast, especially with the highly volatile hydrocarbons!

2) Refractive index

The refractive index nD20 (with the subscript "D" for the wavelength and superscript

"20" for 20 °C) is measured using a thermostatic refractometer. After each meas-urement, the optical window must be cleaned using soft paper tissue andacetone. It must not be scratched!!!

3) IR spectroscopy

The IR spectra of the standards and all sample fractions are measured using anFTIR spectrometer (FTIR = Fourier-Transform-Infrared-) and an IR cell. The cellmust be treated with extreme care because of its price. As the cell windows con-sist of KBr contact with water must be avoided. The cell windows must be cleanedusing soft paper tissue and acetone. They must be kept under dry conditions in adesiccator.

3. ReportDraw a sketch or make a photo of the distillation plant and use it for the detaileddescription of the experimental setup and the procedure in the report.


Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung


CHP3L_02Synthesis of ethyl benzoate (ester synthesis)

1. Objectives and general procedureThe condensation reaction of a carboxylic acid and an alcohol leads to the formationof an ester, with water as by-product. Such reactions are typical equilibriumreactions. Equilibrium can be shifted to the ester side by adding of hygroscopic acids(removal of water) or excess alcohol. In this case, excess alcohol and concentrated sulfuric acid are used. The general reaction equation is:

R2-OH OH2H

+

R1-COOH R1-COOR2+ +

Lower esters are liquids of agreeable odor and are used in the manufacture of perfu-mes. Vegetable and animal fats and oils are glycerol esters of fatty acids (fatty acidtriglycerides).

1.1. Pre-lab preparationOrganic oxygen compounds; properties of carboxylates, carboxylic acids and alco-hols; condensation reaction; solubility, miscibility with water; volatility, hydrogenbonding; extraction; chemical equilibrium; batch; yield; theoretical yield.

Literature:


2) Organic chemistry textbooks

1.2. EvaluationCalculate the theoretical yield and compare your yield with the theoretical and the lit-erature values.

1.3. DiscussionDiscuss yields and the purity of your product.

page 1 CHP3_2: Synthesis of ethyl benzoate 26.03.2008

2. Experimental

2.1. Instruments and glassware500-mL two-neck round-bottom flask, external heating, stirrer, rotary evaporator, 1-L-separation funnel, 1000-mL-beaker, funnel, folded filters, if and when needed:vacuum distillation plant.

2.2. Chemicals

"rein""pure"

xxxxxxxxxxxxxxxxxxxxxxxxcalcium chloride CaCl2sodium sulfate Na2SO4

"rein""pure"

xxxxxxxxxxxxxxxxxxxxxxxxsodium hydrogen carbo-nate NaHCO3

w = 99 % V = 120 mL dichloromethane CH2Cl2

w = 96 % V = 200 mL ethanol C2H5OH

w = 98 % V = 5 mLsulfuric acid H2SO4

"für die Synthese""for synthesis"

0.5 molbenzoic acid

purityamount (volume)Compound

2.3. Procedure

The carboxylic acid (0.5 mol) is dissolved in 200 mL of ethanol w(C2H5OH) = 96 % ina 500-mL two-neck round-bottom flask with reflux condenser. 5 mL of sulfuric acidw(H2SO4) = 98 % are added. The mixture refluxed for 4 h, then cooled to room tem-perature using ice water. The excess ethanol is removed in the rotary evaporator.

The residue is taken up with ca. 200 mL of dichloromethane and extracted twice witha similar volume of cold water, using a 1L separation funnel. The organic phase isthen extracted with saturated sodium hydrogen carbonate solution (caution - mayfoam!) until pH 8 is obtained, and finally with water. The organic phase is collectedand dried over water-free calcium chloride or sodium sulfate overnight in the fridge.The desiccant is removed by filtration, and the solvent is removed in the rotaryevaporator.

The ester can be purified further by vacuum distillation. To assess for purity, therefractive index and an FTIR spectrum are measured.

Literature yield: 80 % of theory for reactive acids

Physico-chemical data:

nD20 = 1.504 ! 0.02

bp.(ambient pressure) = 211-213 °C

IR spectrum


3. Report- including specific reaction equation with structures, calculation of batch and yield,characterization of the product, discussion of yield and purity.

Questions for discussion: Why does the mixture foam when hydrogen carbonate isadded? Why the addition, why not water? Why is the product that pure, even withoutdistillation?

Why is a vacuum distillation preferred for futher purification, and not a distillation atambient pressure? Estimate the ester's bp. at ambient pressure, using a reasonablevalue for its enthalpy of vaporization.


Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung


CHP3L_03Synthesis of a benzoic acid (ester hydrolysis)

1. Objectives and general procedureGeneral reaction equation:

H-OH R2-OHOH

R1-COOR2R1-COOH+ +

ester + water <===> carboxylic acid + alcohol The hydrolysis of esters proceeds via the meachanism of nucleophilic substitution.The nucleophil is the negatively charged hydroxy group OH-. The OH- ion attacks the positively polarized carbon atom of the ester group andreplaces the alcohol(ate). The product is the alkali salt of the carboxylic acid, which iswater-soluble. When the pH of the reaction mixture is decreased, the carboxylic acidpresipitated because of its reduced solubility, as compared to the alkali salt. Ester hydrolysis is promoted at high OH- concentration if the hydrolysis is performedin alkali hydroxide solutions, and not in water. The degree of hydrolysis is then grea-ter than 90 %.The alkali salts of carboxylic acids are soaps. Soaps were in former times producedfrom slaughterhouse wastes, especially from animal fats. Oils and fats (lipids) areesters from fatty acids and the triol glycerol. Naturely, soaps can also be manufactu-red from vegetable oils like olive oil. Industrial lubricants can contain mineral oils or animal/vegetable, res. synthetic, oils.Native oils are not triglycerides but methyl esters, owing to improved technologicalproperties. The process is named "transesterification".

1.1. Pre-lab preparationOrganic oxygen compounds; properties of carboxylates, carboxylic acids and alco-hols; condensation reaction; solubility, miscibility with water; volatility, hydrogenbonding; extraction; chemical equilibrium; batch; yield; theoretical yield.

Literature:


2) Organic chemistry textbooks

page 1 CHP3_3: Synthesis of benzoic acid 26.03.2008

1.2. EvaluationCalculate the theoretical yield and compare your yield with the theoretical and the lit-erature values.

1.3. DiscussionDiscuss yields and the purity of your product.

2. Experimental

2.1. Instruments and glassware500-mL two-neck round-bottom flask, external heating, dropping funnel, reflux con-denser, beakers, stirrer.

w = 10 % dil. hydrochloric acid, dil. HCI

w= 8% V= 150 mL dil. sodium hydroxide solution,dil. NaOH

"für die Synthese"0.3 mol ethyl benzoate

purityamount/volumeCompound

2.2. Procedure In the reaction vessel 150 mL of sodium hydroxide solution, w(NaOH) = 8 %, and0.3 mol of the ester are refluxed for 90 minutes under vigorous stirring. The transpa-rent, single-phase solution is cooled to room temperature using an ice water bath,then 100 mL of cold water are added. Stirring continues, and hydrochloric acidw(HCI) = 10 % is added cautiously until complete precipitation of the acid (app. pH2). The suspension is filtered using a glas filter funnel, and the filtrate is tested for com-plete precipitation (how? explain!). The filter residue is washed three times with smallamounts of cold water. The humid product can be recrystallized directly fromethanol/water. The final product is dried over H2SO4 conc./NaOH in a vacuumdesiccator.

2.3. Yield

Literature yields are 90 % with respect to theory, approximately.

2.4. Physico-chemical dataMelting point mp. = 122°C pH of aqueuos solution < 7IR spectrum

3. Report- including specific reaction equation with structures, calculation of batch and yield,characterization of the product, discussion of yield and purity.


Question for discussion: Why must the reaction mixture be acidified for the product toprecipitate?


Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung


CHP3L_04Electrical conductivity of electrolyte solutions

1. Objectives and general procedureThe electrolyte conductivities of aqeous solutions of a strong and a weak electrolyteare determined with reference to electrolyte concentration. The original data areevaluated for molar conductivties, the validity of Kohlrausch's law, limiting conductivi-ties res. degree of dissociation and dissociation constant.

1.1. Pre-lab preparationInform yourself about: Strong and weak electrolytes, ideal dilutions, conductance(resistance), conductivity (specific, molar, ion, equivalent), (resistivity), degree of dis-sociation, dissociation (equilibrium) constants, conductometry, cell constant, Kohl-rausch's law, Ostwalds's law

Literature:

All textbooks of Physical or Analytical Chemistry, e.g.:

- Atkins P. W.: Physical Chemistry, W.H. Freeman & Company 1997- Atkins P. W., J. Depaula: Physical Chemistry, W.H. Freeman & Co 2001- Atkins, P. W.: Concepts of Physical Chemistry, W.H. Freeman & Company 1995- Atkins P. W.: Physikalische Chemie, Wiley-VCH 2002- Atkins P.W.: Einführung in die Physikalische Chemie, VCH 1993- Atkins, P. W.: Kurzlehrbuch Physikalische Chemie, Wiley-VCH 2001- Hamann C.H., W. Vielstich: Elektrochemie, Wiley-VCH 1998 - Hamann C.H., A. Hamnett, W. Vielstich: Electrochemistry, Wiley-VCH 1997

1.2. Evaluation

For the different dilutions, the specific conductivity κ is plotted versus the molar con-centration. Discuss the resulting curves, are they linear or not?

Estimate the salt concentrations of tap and Geeste water, assuming sodium chloridebeing the only electrolyte present in the water samples. Estimate the acetic acid con-tent of the vinegar assuming that it contains nothing but water and acetic acid.

Calculate the molar conductivities and the limiting conductivities of the electrolytedilutions graphically (if possible). Which are strong, which are weak electrolytes?

1.3. DiscussionApply Kohlrausch's law for the three diluted electrolytes. How great are the limitingconductivities m

0, how great is K? Explain from the results why KCl solutions give the

page 1 CHP3_4: Electrical conductivity of electrolyte solutions 26.03.2008

perfect standards for the calibration of conductivity cells. Discuss your results withreference to literature values.

Calculate the degree of dissociation for the different acetic acid dilutions and plot thisresult versus the molar concentration of acetic acid. Explain the fundamental differ-ence between the degree of dissociation and the dissociation (equilibrium) constant.Plot a theoretical curve using the literature acid dissociation constant (KD(20oC) =1,753 ×10-5 mol/l)! Vice versa, calculate the dissociation constant of acetic acid inaqueous solutions from your results using Ostwald's law and compare the result tothe literature value.

2. Experimental

2.1. Instruments and glasswareConductometer and conductivity cell (cell constants C=1; C = 0.1; ...), volumetricpipettes, volumetric flasks, magnetic stirrer.

2.2. ChemicalsPotassium chloride standard solution c(KCl) = 0.1000 mol L-1, potassium chlorideKCl, sodium chloride NaCl, acetic acid CH3COOH 96 %, tap water sample, Geesteriver water sample, vinegar.

2.3. Procedure The electrolyte solutions listed in Table 1 are to be prepared in a dilution series.

-----(100 %)vinegar

-----(100 %)Geestewater

-----(100 %)tap water1.00.510-15×10-210-25×10-3CH3COOH10-15×10-210-25×10-310-35×10-4NaCl10-15×10-210-25×10-310-35×10-4KCl

c/mol l-1c/mol l-1c/mol l-1c/mol l-1c/mol l-1c/mol l-1Electrolyte

Table 1 Electrolyte dilution series

After calibration with KCl conductivity standards, the conductivities of the electrolytedilutions are measured using the conducivity cell with the appropriate cell constant.

page 2 CHP3_4: Electrical conductivity of electrolyte solutions 26.03.2008

Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung


CHP3L_05Biotechnological ethanol synthesis

1. Objectives and general procedureThe production of bioethanol, e.g. for use as a fuel or fuel component, is performed ina lab-scale biotechnological process using yeast microorganisms. Yeast is a single-cell fungus that can convert glucose to ethanol and carbon dioxide. This enzymaticprocess is called ethanol fermentation and provides the yeast cells with energy.

Ethanol has been made since ancient times by fermentation of sugars. Still half of theindustrial ethanol is made by this process. Recent progress in applied science, tech-nology and manufacturing processes has led to a highly efficient and cost effectiveindustrial production of ethanol, especially for fuel usage.

In this experiment the productivity (catalytic activity) of baker’s yeast (scientific name:“saccharomyces cerevisiae”) is determined by recording the concentration changesof product (ethanol) and reactant (glucose) versus time during the fermentationprocess.

1.1. Pre-lab preparationbaker’s yeast, (ethanol) fermentation, respiration, nutrient media (energy source, car-bon source, nitrogen source), bioreactor (fermentor), bioethanol, fuel ethanol,enzymes (biocatalysts), enzymology, enzyme activity

What is the biochemical equation for ethanol fermentation? What are the molar pro-portions of glucose and ethanol in this equation ? Calculate the theoretical ethanolyield in "g ethanol/ g glucose".

Literature:


2) All general microbiology and biochemistry textbooks

3) Atkins' Physical chemistry, any edition (reaction kinetics)

To provide a state-of-the-art overview of biofuel production:

Kamm, B. et al.(ed.) (2006): Biorefineries - Industrial Processes and Products.Wiley-VCH, Weinheim.

Roehr, M. (2000): The Biotechnology of Ethanol. Wiley-VCH, Weinheim.

page 1 CHP3_5: Biotechnological ethanol synthesis 26.03.2008

Trafton, A. (2006): Engineered yeast improves ethanol production. In: MIT TechTalk (official online newspaper of the Massachusetts Institute of Technology) Vol-ume 51 – Number 12.

Ward, O.P. (1989): Fermentation Biotechnology. Open University Press, MiltonKeynes.

Wyman, C.E. (ed.) (1996): Handbook on Bioethanol: Production and Utilization.Taylor and Francis, Washington DC.

Zaldivar, J., Nielsen, J., Olsson, L. (2001): Fuel ethanol production from lignocel-lulose: a challenge for metabolic engineering and process integration. AppliedMicrobiology and Biotechnology 56, 17-34.

1.2. EvaluationMass balance; masses res. volumes of all (how many) fractions with correspondingboiling points or ranges.

Composition: Compare all measuring data and spectra to those of the pure sub-stances, as measured and/or literature values (if available).

1.3. DiscussionDiscuss the purity of the fractions and the efficiency of the separation. Quantifyroughly the composition of each fraction assuming that compositions (i.e., molar frac-tions) and physical data like the refractive index behave correspondingly. Discuss thedifferent measuring methods with respect to their application in identifying thefractions.

2. Experimental

2.1. Instruments and glasswareBioreactor system consisting of a stirred 1-L-thermostatted vessel with pH-probe andethanol probe, connected with a process control system, magnetic stirrer, high-speed-centrifuge, UV/VIS-Spectrophotometer, µL-pipets, 1.5-mL Eppendorf-cups,1-cm half-micro cuvettes.

2.2. Chemicals and microbial strains

Calciumchloride, 0.1 mol/L sodium hydroxide solution and 0.1 mol/L hydrochloric acidsolution, enzymatic testkit for glucose determination (see attachment), commerciallyavailable baker’s yeast, sterilized glucose solution ß(C6H12O6) = 200 g/L.

2.3. Procedure

1 L of calcium chloride solution c(CaCl2)=0.01 mol/L is prepared and its pH isadjusted to 4.7. The bioreactor vessel is filled with 740 mL of this calcium chloridesolution. The vessel is heated to a temperature of 30°C under stirring. The pH probe,the ethanol probe and the hose for the base-supply (pH control) are mounted on thereactor lid. The process control system is activated and a setpoint value of pH 4.6 isentered. A suspension of 8 g yeast in 10 mL of 0.01 mol/L calcium chloride solution(pH 4.7) is prepared and added to the solution in the vessel. The reaction is startedby adding 40 mL of sterilized glucose solution. Directly after adding the glucose


solution a 1-mL-sample is taken with a µL-pipet and filled into an Eppendorf-cup. Thecells are immediately separated from the solution by centrifugation at 16 x 103 g for5 min. Attention: The load of the centrifuge has to be balanced carefully! After centrifugation, 500 µL of the supernatant solution are pipeted into anotherEppendorf-Cup, for the immediate determination of glucose. (Alternatively, the super-natant solution is frozen for storage, and glucose is determined later.) For analysis,the sample is diluted with deionized water at the ratio of 1:20. The diluted solution isthe sample with respect to the enzymatic glucose testkit.

Note: All volume values referred to in the pipeting table of the testkit instruction mustbe divided by two, otherwise the complete testkit volume would exceed the half-micro-cuvettes volume.

Glucose samples are taken in 20 min intervals.

The signals from ethanol and pH probe are recorded using the process control sys-tem. Ethanol production continues for at least 80 min.

3. Evaluation of results

For converting the ethanol probe’s mV signal into mass concentration values [g/L] agraph from the calibration curve data of the ethanol probe (see Table. 1) must be cre-ated, e.g. by using a spreadsheet software. An empirical function is found to represtnthe data by a regression method. The function's coefficients are used to compute theethanol mass concentration from the experiment. Glucose concentration [g/L], etha-nol concentration [g/L] and pH are plotted in a diagram versus time.

12.0710409.058966.037434.226143.025071.813901.213180.602300.301690.06770.0030

(Ethanol)/g L-1E/mV (100 % gain)

Calibration Curve Data09.02.2007

T=30°C

Table 1 Ethanol probe calibration data

Compute the maximum volumetric production rates of ethanol, Rc(eth)/mol L-1 h-1“ andR (eth)/g L-1 h-1, as related to the reaction mixture volume, from the linear region ofthe correspoding curve, respectively the data in the spreadsheet.

Compute the maximum volumetric consumption rates of glucose, Rc(glu)/mol L-1 h-1“and R (glu)/g L-1 h-1, from the linear region of the curve, respectively the data in thespreadsheet.


Compute the specific production rates of ethanol rc/mol g-1 . h-1 and r /g .g -1 . h-1, asrelated to the yeast mass.

Compute the corresponding specific glucose consumption rates.

Compute the molar and mass ethanol yields , in mol ethanol per mol glucose and inmass of ethanol per mass of glucose.

4. Report (discussion)Compare the practical ethanol yield and the theoretical yield (theoretical yield =100 %) ! Why is it reasonable to expect a practical yield of approximately 100 % ofthe theoretical yield ? Under which circumstances would would you expect a lowerethanol yield ?

5. Attachments


Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung


CHP3L_06Potentiometric determination of chloride

1. Objectives and general procedureChloride is determined quantitatively using the potentiometric method. Like theFajans method, and potentiometry) it is based on the formation of sparingly solubleAgCl.

The samples are:

1) Sodium chloride standard solution (reference concentration),2) tap water3) a Geeste river sample,4) a sample solution prepared from a bakery product (to bring from home)

The potentiometric titration curves (electrode potential E/V vs. V(titrant) are recordedand evaluated for their turning points, i.e. their stoichiometric points.

1.1. Pre-lab preparationPrecipitation equilibria, solubility product, potentiometry, Fajans chloridedetermination.

Literature:


2) Atkins' Physical chemistry, any edition

To bring from home: the bakery product, e.g., a bread roll.

Inform yourself about

a. the sodium chloride contents of Bremerhaven tap water,

b. the expected salt content in the Geeste river, a tidal river not far from the NorthSea and its periodic change (see also: the tide calendar in the internet, http://www.bsh.de/de/Meeresdaten/Vorhersagen/Gezeiten/index.jsp). Theexpected salt content is somewhere between the salt content of freshwater andsea water from the North sea.

c. the salt content of food products, especially bakery products, e.g. inhttp://www.mypin.de/html/sport/Salz.html,

and use this information to estimate the Cl- molar concentration of the samples oranalytes to be titrated.

page 1 CHP3_6: Potentiometric determination of chloride 26.03.2008

1.2. EvaluationThe chloride content of the samples is given as

a. molar concentration c(Cl-)/mol L-1

b. mass concentration (Cl-)/g L-1 and (NaCl)/g L-1 for the fresh water samples,c. for (3), the bakery product only: w(NaCl)/g g-1; as relied to the total mass and the

dry substance content of the bakery product, e.g. a bread roll. d. Additionally, calculate the water content of the bakery product in w(H2O)/g g-1.

1.3. DiscussionCompare the experimental results from both methods with the reference values.Which method has the higher precision? Which is faster? Which has the lower detec-tion limit? Discuss the composition of tidal waters and the consequences if you wantto analyze such water on a regular basis. Discuss the price of bakery products basedon the results of your analysis.

2. Experimental

2.1. Instruments and glaswarePotentiometer, silver electrode, reference electrode, magnetic stirrer, analyticalbalance.

The reference electrode is fragile, must be treated carefully, never dry out, and mustbe stored in sat. KCl solution.

Burettes, volumetric pipettes (25 mL, 1000 mL), pipetting aid, Erlenmeyer flasks,volumetric flasks (1 L), sampler and sample container for Geeste water, mortar andpestle, folded filters, filter funnel.

2.2. Chemicals

silver nitrate solution c(AgNO3) = 1.000 % 10-2 mol L-1, sodium chloride standard solu-tion with given reference concentration.

2.3. Sample preparationTap water: due to the low chloride content, 100.00 mL of the tap water are titratedwithout further dilution!

Geeste water: The Geeste sample must be filtered before analysis. The analyticalprocedure depends on the salt content of the actual sample, if low, see above; ifhigh, you have to dilute it and proceed as described below.

Bakery product: The bakery product (approximately 100 g) is measured out using theanalytical balance, then dried in the drying cupboard until constant mass. The drysubstance is measured out, finely pulverized using mortar and pestle, and dissolvedin dist water. The aqueous solution is filtered. The analyte sample of 25.00 mL istitrated as described below.

2.4. Procedure

Note that due to the adsorption of otherwise dissolved components on the surfacesof the freshly precipitated AgCl (co-precipitation), the composition of the analyte


solution changes slowly and the titrations must be performed rapidly! - Otherwisethere won't be reasonable results. Thus it makes sense to know in advance the orderof magnitude of the sample's chloride content, either by calculation, rough estimationor by a first rough and very rapid titration.

A 25.00 mL sample of the analyte solution is given into a 250 mL Erlenmeyer flask,and is filled up with dist. water to a total volume of 100 mL. A magnetic stirrer isadded, the silver electrode and the reference electrode are installed so that they are(a) immersed in the sample and (b) not destroyed by the moving stirrer. The sampleis titrated with the titrant from the burette, silver nitrate solutionc(AgNO3) = 0.1000 mol L-1). The titration curves are recorded to evaluate the turningpoints graphically. Use a spreadsheet software to evaluate them for their turningpoints via numerical differentiation.

All determinations are repeated twice.

2.5. Evaluation to do in the labAll titrations are immediately evaluated for their stoichiometric points and the corre-sponding molar concentrations.

3. Report (discussion)- accuracy of the measurement

- accuracy of the evaluation (graphical/numerical)

- significance of results (tap water, tidal river water, food products)


Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung


CHP3L_07Chromatography

Theory:

Overview of common chromatography techniques

Three types of chromatography are routinely used in the organic chemistry:

Column Chromatography

Thin Layer Chromatography (TLC)

Gas Chromatography (GC)

In these (and all types of) chromatographies, a mixture is separated by distributingthe components between a stationary phase and a mobile phase. The mixture is firstplaced on the stationary phase (a solid or a liquid) and then the mobile phase (a gasor a liquid) is allowed to pass through the system.

In this experiment you will perform a column chromatography. The intention is toseparate a dye mixture.

Literature: All general, physical, organic and analytical chemistry text books.

Procedure:

Adsorbent: silica gel 60

Eluent mixture: n-Butanol : acetic acid : Water (Mixing ratio = 50 : 10 : 20)

Sample: contains 1 mg/mL Fluorescein and 0,1 mg/mL methyleneblue in eluentmixture

1. Packing the columnFill the empty column with 10 mL of solvent. Weigh 4-5 g of silica gel into a 50-mL-beaker. Place 25-30 mL of solvent in a 100-mL-beaker and slowly add the silica gelpowder, a little at a time, while swirling. Use a glass-rod to mix the slurry, then quicklypour the slurry onto the column. Place an Erlenmeyer flask under the column, openthe plug valve, and allow the liquid to drain into it. Continue to transfer the slurry tothe column until all the silica gel is added. Add more solvent as necessary; the sol-vent collected in the Erlenmeyer flask can be re-used to add more silica gel to thecolumn. When finished packing, drain the excess solvent until it just reaches the toplevel of the silica gel. Close the plug valve. Your column is now "packed."

page 1 CHP3_7: Chromatography 26.03.2008

2. Determining the absorption maxima of the sample compounds (dyes)Generate a VIS-spectra of a fluorescein-solution (0,1 mg/mL in eluent mixture) and amethylene blue-solution (0,01 mg/mL in eluent mixture) with the spectrophotometerfrom 350 to 800 nm against the eluent as blank. The absorption maximum is thewavelength at the highest peak in a spectrum. Use these wavelengths when you ana-lyze your fractions.

3. Loading and Eluting the Chromatography ColumnThe sample (500 µL) is applied to the top of the column. 30 half-micro-cuvettes (asfraction tubes) in a rack are placed directly under the bottom of the column. Thepinch clamp is opened and the first fraction is collected in the first cuvette. The frac-tion size should be one mL, so each cuvette has to be changed when it’s filled to thislevel. Cover each cuvette with parafilm to prevent the liquid from evaporation. Whenthe sample has just drained into the adsorbent, carefully overlay the column witheluting solvent using a pasteur pipet. Continue adding solvent at the top by startingthe peristaltic pump and collecting fractions at the bottom until the compounds eluteat the bottom.

Never let the solvent level drop below the top of the adsorbent (adjust the pumpspeed to an appropriate level). The separation is finished when both column and elu-ent are colorless.

The absorption of each fraction at the absorption maxima (of fluorescein and methyl-ene blue) is measured against the pure eluent as blank.

4. Evaluation

Use the absorption values obtained from determining the absorption maxima to cal-culate the mass concentrations of the dyes in each fraction. Draw a chromatogramby plotting the concentration against the elution volume.

5. DiscussionCalculate the balance for the separation (input vs. output). What can be said about itsefficiency?

page 2 CHP3_7: Chromatography 26.03.2008

Total (20)F&S(3)

Disk.(3)

Exp.(3)

Theorie(3)

Durch-führung (8)

Bewertung


CHP3L_08Polmerization of Methylmethacrylate

1. Objectives and general procedurePolymethylmethacrylate (PMMA) is synthesized in a radical polymerization reactionin three different batches with respect to the monomer/radical initiator ratio. Themolecular weights (or molar masses) of the products are determined using viscome-try. The degree of polymerization is determined as a function of the monomer/radicalinitiator ratio.

1.1. Pre-lab preparationRadical chain reaction, radical polymerization, ionic polymerization, initiator, additionpolymers, condensation polymers, degree of polymerization, solubility of organiccompounds, physico-chemical properties, fluid viscosity, viscometry.

Literature:

1) All general chemistry textbooks,

2) Atkins' Physical chemistry, any edition,

3) Organic chemistry textbooks.

1.2. Evaluation: Calculation of the molecular weight of a polymer fromviscosity data

The viscosimetric method for polymer molecular mass determination by Staudinger isbased on the fact that linear macromolecules increase significantly the viscosity of asolvent even if in diluted solution. The viscosity of the solution increases with increas-ing polymer concentration. However, the method can only be applied for linear chainmacromolecules, it fails for spheroid or highly branched molecules like globular pro-teins or glucogens (liver sugars).

For the calculation of the molar mass of the solute, i.e. the polymer, the viscosities ofthe pure solvent 0 and the solution, , are measured, and the "specific viscosity" sp

is calculated using eq. (1):

(1)sp =− 0

0

If the chosen viscometer is optimized regarding size and capillary diameter and thepolymer concentrations are low (approximation: the density of the pure solventequals the density of the solution), sp can be calculated directly from the flow times,i.e.:

page 1 CHP3_8: Polymerization of Methylmethacrylate 26.03.2008

(2)sp =t − t0

t0

Dividing sp by the polymer mass concentration gives the "reduced specificviscosity" sp/ . As the latter value depends on concentration, a limiting viscosity forinfinite dilution (or intrinsic viscosity) ∞ is determined as given in eq. (3):

(3)∞ =d0

lim sp

With sp being dimensionless ∞ has dimension of -1, i.e. (L g-1) respectively (100 mLg-1), or mL g-1. For not to confuse the dimensions the mass concentration dimensionsmust be noted!

The limiting value ∞ for d 0 is determined by graphical extrapolation: the calculatedsp/ ratios are drawn to a diagram versus the mass concentrations , for example 10,

5, 2.5 and 1.25 g/L. After extrapolating the resulting graph to = 0, ∞ can be readfrom the ordinate. Generally, linear graphs describe the viscosities of polymer solu-tions with low or medium molecular masses, whereas the graphs become nonlinearor curved for high molecular masses.

Additionally there are some empirical relations for the calculation of the limiting vis-cosity ∞ from a single viscosity measurement, for example:

; with Kη = 0.28 (4)∞ = sp/1 +K $ sp

The advantage of this evaluation is that the number of measurements is limited to asingle viscosity determination. For low polymer concentrations, Kη does not dependon the type of the solvent and the composition of the polymer.

Another equation describes the dependency of the limiting viscosity ∞ and themolecular mass:

; or: ∞ = K $ Ma

(5)log ∞ = logK+a $ logM

The constant K and the exponent a do again not depend on polymer, solvent or tem-perature.

The molecular masses are calculated as follows:

1) Calculate sp as given in eq. (2).2) Calculate ∞ using eq. (4), in g/mL).3) Calculate the molecular masses M using eq. (5). Constants K and a for polyme-

thylmethacrylate in acetone: K=0.096 mL/g and a=0.69 (at 25°C).

1.3. Representation of results in diagrams

1) Molecular mass vs. initiator concentration for all three batches,2) Degree of polymerization vs. monomer/radical initiator ratio

1.4. Discussion

A theoretical assumption is that each initiator molecule initiates one polymer mole-cules (why?). Can that assumption be proven? If not, what might be the reason?


2. Experimental

2.1. Instruments and glaswareCapillary (Ubbelohde) viscometers

2.2. Chemicals and instrumentsBatch: 3 batches with 5.0 to 10 mL of methylmethacrylate per batch, benzoic peroxi-de as initiator (ask lab instructor for exact amounts of methylmethacrylate andinitiator!)

Molar mass determination: acetone, polymer samples of all batches

Health and safety at work (by German law): methyl methacrylate; C5H8O2, bp. = 101o

C; Giftklasse CH; MAK (1996): 205 mg m-3; entzündliche flüssige Stoffe, Gruppe A;R: 11-37/38-43 ; S: 24-37-46 ; Entsorgung: 1, WGK 1, protective gloves, fume cup-board!

2.3. ProcedurePolymethylmethacrylate synthesis

3 batches with different monomer/initiator ratios are prepared in sample containerswith covering lids. Ask the lab instructor for the exact ratios!. The polymerizationreaction is performed over two nights period in the drying cupboard at 70 °C.

Molecular mass determination of PMMA using viscometry

After pulverizing, 125 mg of each polymer sample are dissolved in acetone in a25.00 mL volumetric flask. The viscosities of the pure solvent and the polymer solu-tions are determined at 25 °C, using a capillary viscometer (Ubbelohde viscometer).

At the end of experiment all the glassware, including the capillary, have to be cleanedby rinsing with acetone (do not use water) and left under the fume cupboard for dry-ing. Ask the lab instructor for the exact procedure.


Documents

CHP3 Lab Lab Instructions