Green Chemistry Workshop #2:

Analytical Chemistry I

Green Chemistry Workshop #2:

Analytical Chemistry I

US – Thai Distance Learning Program

January 27, 2010

Professor Kenneth M. Doxsee

University of Oregon

The Principles of Green Chemistry

1. Prevention

2. Atom Economy

3. Less Hazardous Synthesis

4. Designing Safer Chemicals

5. Safer Solvents and Auxiliaries

6. Design for Energy Efficiency

7. Renewable Feedstocks

8. Reduce Derivatives

9. Catalysis

10. Design for Degradation

11. Real-time Analysis

12. Inherently Safer Chemistry

Oxygen Content of Air

Premise• Measuring the volume change of air in contact

with an Fe(II) solution provides a measure of the percent O2 in air.

Chemical Concepts • Acidic, basic, amphoteric oxides; direct

combination reactions; preparation and properties of O2; physical nature of reactants; acid and base properties; stoichiometry; redox; gas solubility; volume.

Background

• Fe(II) oxidizes slowly at pH < 7

• Fe(II) oxidizes quickly at pH > 7.

• This allows us to prepare solutions of Fe(II) in contact with air, then to induce the reaction with O2 when we are ready.

Reaction Chemistry

Fe(II) + O2 Fe(III)

FeSO4 + O2

pH < 7slow

Fe(III)pH > 7

fast

Fe(OH)3, Fe2O3, FeOH(SO4), Fe2(SO4)3, …?

Materials

Syringe image: http://www.nordiccell.com/embryo-transfer/images/HSW/HSW-1-ml.jpgBeaker image: http://www.chemistry.wustl.edu/~courses/genchem/Labs/Quant/images/150mlBeakers.gifTubing image: http://shop1.actinicexpress.co.uk/shops/partsforaircraft/images/catalog/tygon-1.jpg

two 1 mL syringes

0.4 mL of 0.2 M FeSO4 1.0 mL of 2 M NaOH

1 cm tubing

Apparatus and Procedure

1 cm flexible transparent tubing(filled with 2 M NaOH)

0.4 mL of 0.2 M FeSO40.4 mL of 2 M NaOH+0.5 mL of air

measure initial volume of air carefully!!

measure final volume of air carefully!!

Calculations

Check limiting reagent:

0.4 ml of 0.2 M FeSO4 = 8.0 x 10-5 moles Fe(II)0.5 mL of air ~ 0.1 mL of O2 = 4.1 x 10-5 mole O2

PV = nRTN = PV/RT = (760 mm-Hg)(0.001 L)

(62.364 L-mmHg-mol-1-K-1)(298 K)

There is enough Fe(II) to consume all the O2.

R = 0.0821 L-atm-mol-1K-1

= 62.364 L-mmHg-mol-1-K-1

Calculations

Vfinal - Vinitial = VO2

% O2 in air = (VO2/Vinitial) x 100%

Laboratory Safety

Accident: An unexpected and undesirable event, especially one resulting in damage or harm.

Image from: http://facilitysigns.wordpress.com/category/signs-and-labels/

LABORATORY SESSIONBreak for ….

Calculations

Vfinal - Vinitial = VO2

% O2 in air = (VO2/Vinitial) x 100%

Other Approaches

• Orsat analyzers (alkaline pyrogallic acid and/orchromium (II) chloride solutions)

• Electrochemical determinations• Quenching of room-temperature phosphorescence• Quenching of luminescence• Use of a paramagnetic oxygen analyzer

Hazardous reagents (exposure risks, waste disposal) Specialized equipment (expensive to purchase and operate)

Orsat analyzer image: http://img.tradeindia.com/fp/1/051/525.jpgParamagnetic O2 analyzer image: http://www.fik-net.co.kr/prod/gas-de.gif

Green Relevance

Green Concepts• Safer chemicals and solvents – compare reagents used in other

determinations of oxygen content.

• Prevention of waste.

• Consider Green Principles

– #1 (prevent waste)

– #2 (atom economy)

– #3 (use less hazardous substances)

– #8 (avoid derivatives)

– #10 (design for degradation)

– #11 (real time monitoring)

– #12 (use substances in forms that minimize hazards).

CaCO3 Content of Eggshells

Premise• CaCO3 reacts with acids to produce CO2.• By measuring the volume of CO2 produced, we can

determine how much CaCO3 was present in a sample of eggshell of known mass.

Chemical Concepts • Decomposition reactions; reactivities of oxides;

preparation of CO2; acid-base properties; stoichiometry; gas law.

Background

• Eggshells are constituted primarily of calcite – a crystalline form of CaCO3.

• Shell formation is governed by LeChatelier´s principle. Carbonate ions are produced by:

CO2(g) + H2O CO⇄ 2 (aq) H⇄ 2CO3

H2CO3 H+ + HCO⇄ 3-

HCO3- H+ + CO⇄ 3

2-

• Shell and membranes production occurs in a gland of the urogenital system of the female bird:

CO32-(aq) + Ca2+(aq) CaCO⇄ 3(s)

Reaction Chemistry

CaCO3(s) + 2H+(aq)

Ca2+(aq) + H2O(l) + CO2(g)

• If the eggshell is treated with an acid, it will dissolve through the reverse of the process by which it is formed.

• By measuring the volume of CO2 produced, we can determine how much CaCO3 was present.

Materials

Eggshell image: http://www.faqs.org/photo-dict/photofiles/list/859/1289egg_shell.jpgScale image: http://www.popgadget.net/images/kitchen-scale-open.jpgMortar and pestle image: http://www.ancientlight.info/products/images_stones/LMORL.jpgPlastic caps image: http://www.sks-science.com/images/240804LRG.jpgSyringe image: http://www.refillsupermarket.co.uk/images/serringue60.jpgBeaker image: http://www.chemistry.wustl.edu/~courses/genchem/Labs/Quant/images/150mlBeakers.gif

10 mL 3N HCl

0.2 g crushed egg shell

Apparatus and Procedure

measure final volume

measure volume

10 mL 3N HCl

CalculationsVfinal - Vinitial = VCO2

PV = nRT

n = moles of CO2 = PV/RT = moles of CaCO3 in sample

If eggshell were pure CaCO3 (MW 100.09 g-mol-1):

x.xx g x 1 mole/100.09 g = y.yy mole

% CaCO3 = (n/y.yy) x 100% =

R = 0.0821 L-atm-mol-1K-1

= 62.364 L-mmHg-mol-1-K-1

Laboratory Safety

Accident: An unexpected and undesirable event, especially one resulting in damage or harm.

Image from: http://facilitysigns.wordpress.com/category/signs-and-labels/

LABORATORY SESSIONBreak for ….

CalculationsVfinal - Vinitial = VCO2

PV = nRT

n = moles of CO2 = PV/RT = moles of CaCO3 in sample

If eggshell were pure CaCO3 (MW 100.09 g-mol-1):

x.xx g x 1 mole/100.09 g = y.yy mole

% CaCO3 = (n/y.yy) x 100% =

R = 0.0821 L-atm-mol-1K-1

= 62.364 L-mmHg-mol-1-K-1

Green Relevance of the CaCO3 Experiment

Green Concepts• Waste as a feedstock.

• Renewable feedstocks.

• Consider Green Principles– #1 (prevent waste)

– #7 (renewable feedstocks)

– #3 (use less hazardous substances)

– #11 (real time monitoring)

– #12 (use substances in forms that minimize hazards).

Questions and Discussion

Image from: http://www.legis.state.wi.us/senate/sen11/news/images/questions.jpg

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