CHAPTER 12 EQUILIBRIUM CONDITIONS IN MULTICOMPONENT SYSTEMS
12.4 COLLIGATIVEPROPERTIES OF ADILUTESOLUTION 379
BIOGRAPHICAL SKETCH
Franc ̧ois-Marie Raoult (1830–1901)Raoult was a French physical chemist best
known for his painstaking measurements of the
freezing points and vapor pressures of dilute
solutions.
Raoult was born in Fournes-en-Weppes
in northern France into a family of modest
means—his father was an official in the local
customs service. He supported himself with
various teaching posts until he was able to at-
tain his doctor’s degree from the University of
Paris in 1863.
Raoult began teaching at the University of
Grenoble in 1867, and three years later was ap-
pointed Professor and chair of chemistry. He
remained in Grenoble for the rest of his life.
He was married and had three children, two of
whom died before him.
His strength was in experimental measure-
ments rather than theory. He constructed most
of his own apparatus; some of it was displayed
in Paris at the Centennial Museum of the Uni-
versal Exposition of 1900.a
In all Raoult published more than 100 pa-
pers based on his measurements. The research
for his doctoral thesis, and later at Grenoble,
was on the thermochemistry of galvanic cells.
His first measurements of freezing-point de-
pressions appeared in 1878. He pointed out
the advantages of determining the molar mass
of a substance from the freezing point of its
dilute solution, and gave specific examples of
this procedure. He was the first to show exper-
imentally that the freezing-point depression of
a dilute aqueous solution of an electrolyte is
proportional to the number of ions per solute
formula unit (Eq.12.4.12).Starting in 1886 Raoult began publishing
his measurements of the vapor pressures of di-
lute solutions of nonvolatile solutes. He used
two methods: (1) For a highly-volatile solvent
such as diethyl ether, the solution sample was
introduced above a mercury column at the up-
per closed end of a vertical barometer tube,
and the pressure determined from the height of
the column.b(2) The solution was placed in a
heated flask connected to a reflux condenser,
and the pressure was reduced at the desired
temperature until boiling was observed.c
His results for diethyl ether as the solvent
led him to propose the relationf f
0
fN D0:01,
wherefandf^0 are the vapor pressurespAand
pAof the pure solvent and the solution, respec-
tively, both at the same temperature, andN
is one-hundred times the solute mole fraction
xB. This relation is equivalent to the Raoult’s
law equationpA D xApA(Eq.9.4.1). He
wrote:d
With a view to ascertain whether this remark-
able law is general, I dissolved in ether com-
pounds taken from the different chemical groups,
and chosen from those whose boiling points are
the highest; the compounds having molecular
weights which are very widely different from
one another; and I measured the vapor pressures
of the solutions obtained. In every case I found
... that the ratiof f
0
fN is very nearly 0.01.
His measurements with dilute solutions of
nonelectrolyte solutes in various other sol-
vents, including benzene, ethanol, and water,
gave the same results.e He was pleased that
his measurements confirmed the theory of so-
lutions being developed by J. H. van’t Hoff.
Raoult’s work brought him many honors.
He was most proud of being named Comman-
der of the French Legion of Honor in 1900.
Sir William Ramsey described Raoult’s per-
sonality as follows:f
Though modest and retiring, Raoult’s devotion
to his work, dignity of character and sweetness
of temper gained him many friends. He was not
an ambitious man, but was content to work on,
happy if his discoveries contributed to the ad-
vancement of science.
aRef. [ 16 ]. bRef. [ 139 ]. cRef. [ 140 ]. dRef. [ 139 ]. eRef. [ 140 ]. fRef. [ 137 ].