chemistry 125: lecture 20 october 20, 2010 lavoisier’s analysis (1789) dalton’s atoms (1801)...

Chemistry 125: Lecture 20October 20, 2010

Lavoisier’s Analysis (1789) Dalton’s Atoms (1801)

Berzelius, Gay-Lussac, & Davy (1805-1830)

Wöhler’s Isomerism (1828)

Elemental analysis was the technique for determining the composition of organic

compounds. Lavoisier's early combustion and fermentation experiments showed a new,

though naïve, attitude toward handling experimental data. The most prominent chemist in

the generation following Lavoisier was Sweden’s J. J. Berzelius. Together with Gay-Lussac

in Paris and Davy in London, he discovered new elements and improved Dalton’s atomic

weights as well as combustion analysis for organic compounds. Invention of electrolysis led

not only to discovering new elements but also to the theory of dualism, whichheld that

elements were united by electrostatic attraction. Wöhler’s report on the synthesis of urea

revealed a persistent naiveté about treating quantitative data. His discovery of isomerism

made it clear that there was more to chemical substances than which atoms they contained

and in what ratios.For copyright

notice see final page of this file

Preliminary

Lavoisier’s Bookkeeping

72 grains = 1 gros8 gros = 1 ounce = 28.35 g

Proximate

Ultimate

Lavoisier’s BookkeepingProximate

Ultimate

Lavoisier’s Bookkeeping

after

before

Hydrogen GeneratorRed-hot Glass Tube

Water

28 grains Carbon

Water

Water (less 85.7 grains)

144 cu. in. (100 grains) Carbonic Gas380 cu. in. (13.7 grains) Flammable Gas

Carbon + Water 28 gr. 85.7 gr.

= Carbonic Gas + "Hydrogen" 100 gr. 13.7 gr.

"I have thought it best to correct by calculationand to present the experiment in all its simplicity."

157

313

103

9.4from 28 gr. C

(modern theory)

Where did they go?+ += !

1.38 g

Traitépp. 88-92

Facts Ideas

Words

Lavoisier Contributions

Elements

Conservationof Mass

Oxidation

Radical/Acid

Salts

Apparatus

QuantitationMassvolume

Substances

Reactions

Meaningful NamesElement - Oxidation State - Salt Composition

-ous, -ic, -ide, -ite, -ate

Clarity

“[Chemistry's] present progress, however, is so rapid, and the facts, under the modern doctrine, have assumed so happy an arrangement, that we have ground to hope, even in our own times, to see it approach near to the highest state of perfec-tion of which it is susceptible.”

Lack of Imagination

"It took them only an instant to make

this head fall, but a hundred years

may not suffice to make another like it."

"Il ne leur a fallu qu’un moment pour faire

tomber cette tête, et cent années peut-être ne suffiront pas pour

en reproduire une semblable."

Lavoisier Guillotined May 8, 1794 Age 50

"The Republic has no need of geniuses.”

But all of his equipment (including 80 pounds of mercury)

was seized for The People.

Boyle Lavoisier√

√

John Dalton

Why do gases of different density remain mixed rather

than stratifying?

amateur meteorologist

1801

Continental European scientists proposed that different gases attract one another.

"the atoms of one kind did not repel the atoms of another kind"

Atom“Heat Envelope”

Matched Lines

Repulsion

Mismatch

Reduced

Repulsion

Substituteshomorepulsion

for heteroattraction

Atoms Explain Analyses:

Definite Proportions

Equivalent Proportions

Multiple Proportions

Pure compounds always have the same weight ratio of their elements.

If a parts of A react with b parts of B,and a parts of A react with c parts of C,…

If two elements form several compounds,their weight ratios are related by simple factors.

and d parts of D react with b parts of B,then d parts of D react with c parts of C.

=

Definite Proportions?

Joseph Louis PROUST(1754-1826)

Claude Louis BERTHOLLET

(1748-1822)

NON! OUI !

metal alloysnatural "organic" materials "chemicals"

Multiple Proportions

O/C

2.57

1.27

O/N

0.58

1.27

2.39

Oxides of Carbon %C %O

28 72

44 56

Carbonic Acid (1801)

Carbonous Acid (1789)

Oxides of Nitrogen %N %O

63.30 36.70

44.05 55.95

29.50 70.50

Nitrous Oxide (1810)

Nitrous Gas (1810)

Nitric Acid (1810)

[1]

2.19

4.12

2.02

[1]

Rel.

Rel.

integral values consistent with simple atomic ratios%err

of (O/C)vs. modern

-4

-5

-2

+11

+11

%errof (O/N)vs. modern

Great scientists focus on the key factors despite errors.(Greatness : Key :: Chicken : Egg)

~2

~4

~2

Genealogy Top

Berzelius etc.

√

BerzeliusJöns-Jakob

BERZELIUS(1779-1848)

Organic & Mineral

Analysis

Dualism(double decomposition)

Electrolysis

Notation forComposition

Teaching, Writing& Editing

Textbook(1808)

2000 compounds in 6 years!

Good Atomic Weightsfor 50 elements!

Notation for Composition

Alchemy

Dalton

Berzelius

ChemicalSymbolsof 1774(Sweden)

1774 Symbols

“When only one combination of two bodies can be obtained, it must be pre-sumed to be a binary one, unless some other cause appear to the contrary.”

ChemicalSymbolsof 1774(Sweden)

HO HN NO HC OC

N2O NO2 CO2 CH2

H N C O P S Mg CaNa K Sr Ba Fe Zn Cu Pb

Ag Pt Au Hg(Corresponding Berzelius Symbols)

Dalton Notation(1808)

http://webserver.lemoyne.edu/faculty/giunta/dalton.html

NO3 SO3 SH3 C3H

“When four…one binary, two ternary, and one quarternary, &c.

Latin (international)

Analytical (NOT structural)

Berzelius Notation(1811)

Dalton’s Logic

N2O NO2 CO2 CH2

NO3 SO3

SH3 C3H

When three…a binary, and the other two ternary. ”

“When two combinations are observed, they must be presumed to be a binary and a ternary…

Abbreviations: Dots denote O atoms

= KO CrO3

Superscripts denote numbers of atomsBenzoic should be H10C14O3 (“acid” as anhydride)

Didn’t catch on

BerzeliusJöns-Jakob

BERZELIUS(1779-1848)

Organic & Mineral

Analysis

Dualism(double decomposition)

Electrolysis

Notation forComposition

Teaching& Writing

Textbook(1808)

2000 compounds in 6 years!

Good Atomic Weightsfor 50 elements!

Atomic Weights and Equivalents

Dalton’sAtomic Weights

(1808) Weights

15579

13

/1 /2 /3 /2 /3 /2

% err

9 9

16 5 5

12

2009

H 1C 12N 14O 16P 31S 32

Silicon ChlorideSiCl T. Thomson

SiCl2 L. Gmelin

SiCl3 J. J. Berzelius

SiCl4 Wm. Odling?

Joseph Louis Gay-Lussac(1809)

Oxidation of Sugar, etc. with NaClO3

Cleans up Lavoisier's Mass Balance

1.9989 volumes of hydrogen per

1.0000 volumes of oxygen Water gives

3.08163 volumes of hydrogen per

1 volume of nitrogen Ammonia gives

Alternative to Dalton's Law of Greatest Simplicity

1804 - 7,016 m(record for 50 years)

(1778-1850)

Established thatatmospherecompositionis invariant

with altitude.

EilhardMitscherlich

(1794-1863)

Goniometer measures angles between crystal faces.

Relating Crystal Shape toChemical Proportions (formula)

Isomorphism of (NH4)2HAsO4 / (NH4)2HPO4

(1820-21)

144336644

1371837424

10231835

Difference (1/10 °)(same shape)

Isomorphism provided definitive atomic weights ratios for some atom pairs.

Need for relative atomic weights:

Is water HO (Dalton)

or H2O (Gay-Lussac)?

As atoms must play exactly the same role in arsenates that P atoms play in phosphates.

100 g of N,O,H combines with 30.64 g P, or 78.11 g As

As atom 2.55 times as heavy as P atom(neither 1.275 nor 5.10 times as heavy)

Berzelius’sTable ofatomic & molecular weights

(1831) Weights

Based on O = 100 or H2 = 1

O = 15.9994

[15.999]

0.998 (-1.0%)

14.162 (-1.0)

32.185 (0.4)

30.974 (1.3)

Bars denotedoubled atoms

Scaled to modern

discrepancy from modern

value

10-fold increase in accuracy from Dalton!

CombustionAnalysis

Berzelius Analysis

(1) Tube 1/2” diameter (Fig 1) charged with dried powder containing: ~0.5 g of organic substance to be analyzed,

3 g NaClO3 (Gay-Lussac’s O2 source), 50 g NaCl (to moderate reaction by dilution).

(2) Neck of tube heated and drawn out (Fig 2)

(4) Assembled (Fig 6) so that gases (O2, CO2) that exit drying tube will bubble into bell-jar containing Hg

with floating bulb (Fig 5) holding KOH (to absorb CO2) and closed with permeable glove leather (to keep out Hg).

Improved Method of Combustion Analysis

(3) Joined (Fig 4) to water-collecting bulb (Fig 3) and CaCl2 drying tube with rubber tubing

Berzelius Analysis

(6) To be certain the KOH absorbs all of the CO2 through the glove leather, wait 12 hours after the mercury stops rising in the bell jar before disassembling and weighing.

(5) Build fire in brick enclosure to heat tube slowly from near end to far. Tube wrapped with metal sheet to keep it from popping when it softens at red heat under the pressure necessary to bubble through Hg.

Improved Method of Combustion Analysis

O2

KOHCO2

Electricity

New York Public Library http://seeing.nypl.org/152t.html

N2O at theRoyal Institution

London, 1802

HumphryDavy

Pile 1799

VoltaBattery of Berzelius

1807-8Humphry Davy

Big Scienceat London’s

Royal Institution

Electrolysis

Cu Zn “couple”

1.1 v

301

v

26 v

110 v

165 v

Davy (1808)

I acted upon aqueous solutions of potash and soda, saturated at common temperatures, by the highest electrical power I could command, and which was produced by a combination of Voltaic batteries belonging to the Royal Institution, containing 24 plates of copper and zinc of 12 inches square, 100 plates of 6 inches, and 150 of 4 inches square…

…though there was a high intensity of action, the water of the solutions alone was affected, and hydrogen and oxygen disengaged with the production of much heat and violent effervescence.

Davy (1808) The presence of water appearing thus to prevent any decomposition, I used potash in igneous fusion. By means of a stream of oxygen gas from a gasometer applied to the flame of a spirit lamp, which was thrown on a platina spoon containing potash, this alkali was kept for some minutes in a strong red heat, and in a state of perfect fluidity. The spoon was preserved in communication with the positive side of the battery of the power of 100 of 6 inches, highly charged; and the connection from the negative side was made by a platina wire. By this arrangement some brilliant phenomena were produced. The potash appeared a conductor in a high degree, and as long as the communication was preserved, a most intense light was exhibited at the negative wire, and a column of flame, which seemed to be owing to the development of combustible matter, arose from the point of contact.

Davy (1808)

A small piece of pure potash, which had been exposed for a few seconds to the atmosphere, so as to give conducting power to the surface, was placed upon an insulated disc of platina, connected with the negative side of the battery of the power of 250 of 6 and 4, in a state of intense activity; and a platina wire, communicating with the positive side, was brought in contact with the upper surface of the alkali.

…small globules having a high metallic lustre, and being precisely similar in visible characters to quick-silver, appeared, some of which burnt with explosion and bright flame, as soon as they were formed, and others remained, and were merely tarnished, and finally covered by a white film which formed on their surfaces.

Napoleon’s Response (via Gay-Lussac)

1807-8Humphry Davy

Big Scienceat London’s

Royal Institution

600 1 kg Cu plates600 3 kg Zn plates

2.6 tons of metal

~650 v

“with that rapidity which characterised all his motions, and before the attendants could interpose any precaution, he thrust the extreme wires of the battery under his tongue, and received a shock which nearly deprived him of sensation. After recovering from its effects, he quitted the laboratory without making any remark, and was never afterwards heard to refer to the subject.” from: “The Life of Sir Humphry Davy, Bart.”

2,200 v

Li Be B

Na Mg Al

K Ca Ga

Rb Sr In

Cs Ba Te

Electricity supplied more than new elements...It also supplied the

organizing principle for

Dualism

ChemicalSymbolsof 1774(Sweden)

1774 Symbols

Mix with Caustic Soda

"Double Decomposition"

A B + C D A D + C B+ + + +- - - -

Explained by Electricity

Dualism

CuSO42 NaOH Na2 SO4 Cu (OH)2+ +

precipitate

“Electronegativity”

First use in English (according to O.E.D.)

1837 J. D. Dana Syst. Mineral. 82 When chemistry has so far advanced, that the relative electro-negativity, (if I may so call it,) or electro-positivity, of the several elements, is fully known,..we shall probably be able to construct a natural arrangement of minerals on chemical principles.

J. D. Dana1813-1895

son-in-lawof Benjamin

SillimanDana House

1849

Genealogy Top

Wöhler/Liebig

to J.J. Berzelius Heidelberg, 17 July, 1823

“Having developed the greatest respect for you through studying your writings, I have always thought it would be my greatest good fortune to be able to practice this science under the direction of such a man, which has always been my fondest desire.

Although I earlier had planned to become a physician…”

With the greatest respect

F. Wöhler from Frankfurt am Main

Friedrich Wöhler(1800-1882)

Letter to Berzelius (1837)

“To see this old friend [Palmstedt] again, especiallyhere [in Göttingen], was a real delight. He was just the same old guy, with the sole exception that he no longerwears the littletoupee swept up over hisforehead ashe used to do.”

1828

Urea&

Isomerism(problems for Monday, Oct. 25 - see web readings)

Wöhler to Berzelius (1828)

"Perhaps you still remember the experiment I carried out in that fortunate time when I was working with you, in which I found that whenever one tries to react cyanic acid with ammonia, a crystalline substance appears which is inert, behaving neither like cyanate nor like ammonia."

"Ammonium Cyanate"from Double Decomposition

NH4 Cl + Ag OCN NH4 OCN + Ag Cl+ + + +- - - -

NH3

NaOH

OCNH

H+ Pb++

Pb(OCN)2

HNO3

Brilliant Crystal Flakes(Just like those from Urea + HNO3)

Not like an ammonium

salt!

Not like a cyanate salt!

Might Ammonium Cyanate Be Urea?

Wöhler to Berzelius: "I recently performed a small experiment, appropriate to the limited time I have available, which I quickly completed and which, thank God, did not require a single analysis."

Berzelius to Wöhler: "It is a unique situation that the salt nature so entirely disappears when the acid and ammonia combine, one that will certainly be most enlightening for future theory…"

Experimental Candor?Prout did dry-lab by making an approximate analysis

and reporting results “corrected” by his theory!better than Berzelius’s Theorytruncated instead of

rounding up

Urea had already been Analyzed

ProutAtoms

1121

NCHO

Total

Dr. Prout(1817)

46.65019.9756.67026.650

99.875

46.7820.196.59

26.24

99.80

Recalc.(from

Berzelius)

46.78120.19806.59526.425

100.000

Discrepancies <2% identical

Dislectic Error(& he didn't notice!)

Prout’s Atomic Weight Theory: H = 1 ("protyle" ) C = 6 ; O = 8 ; N = 14

Prout N2 by volume: "6.3 cubic inches"

?99.945

(added wrong)

46.6520.00

6.7126.64

100.00

Modern

Prout’s Experiment

Moral: Don’t dry-lab! (like Lavoisier)Just Lucky?Prout’s theory was better than Berzelius’s experiments!

Paragon of accuracy and honesty

NH4OCN(calculated by Wöhler

from Berzelius atomic weights)

?

Ammonium Cyanate to Urea

H N H

H

H

N C O

H N

H

H

N C OH

H

N HH

N C OH

H

N HH

N C OH

n*

n *

n*

poor overlap probably

intermolecular

Can ammonium cyanate exist?

ResonanceStructures!

NH2

H2NC

OHH

attack *

attack *

C=O very stable (lore)

Dunitz, Harris, et al. (1998)

Wöhler on Isomerism (1828) "I refrain from all the considerations which so naturally suggest themselves from this fact, especially in respect to the composition ratios of organic substances and in respect to similar elemental and quantitative compositions among compounds with very different properties, as may be supposed, among others, of fulminic acid and cyanic acid and of a liquid hydrocarbon and the olefiant gas, and it must be left to further investigations of many similar cases to decide what general laws can be derived therefrom."

On the Composition of Tartaric Acid and Racemic Acid (John's Acid from the Vosges Mountains), on the Atomic

Weight of Lead Oxide, together with General Remarks on those Substances with have the Same Composition but

Different Properties. by J. J. Berzelius (1830) "I have thought it necessary to choose between the words : homosynthetic and isomeric substances. The former is built from homos, equivalent, and synthetos, put together; the latter from isomeres has the same meaning, although it only properly says put together from the same pieces. The latter has the advantage with respect to brevity and euphony, and thus I have decided tochoose it." "By isomeric substances I understand those which possess the same chemical composition and the same atomic [molecular] weight, but different properties."

X-Ray showed thatthese crystals are

Calcium Tartrate • 4 H2O

There is more to chemistry than analytical

COMPOSITION!Now we know the importance of

atomic arrangement, or STRUCTURE:

CONSTITUTION

CONFIGURATION

CONFORMATIONbut we need to be patient.

End of Lecture 20

October 20, 2010

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