Physico-Chemical Studies Of Solutions Of Some Acids In Acetone

Abstract

The work of Hotz showed the lack of knowledge of the

behaviour of electrolytes in acetone solutions as well as

the uncertainty as to the pos~ibility of preparing anhydrous

acetone and the stability of this solvent, if it

could be prepared.

An extensive study was therefore undertaken in which

the efficiency of various desiccants vJas studied in producing

acetone as anhydrous as could be obtained.

A very efficient still was designed and the average

water content of the acetone produced was of the order of

0.006 per cent which is much lower than reported by any

previous investigator. Moisture determinations were

done using a modified Karl Fischer reagent.

Stability studies of "anhydrous" acetone extending

over a period of about fifteen months showed·no remarkable

increase in the moisture content and it was con•

eluded that "anhydrous" acetone, if treated with care, is

exceptionally stable to self-condensation.

Hydrogen chloride was shown to be an extremely weak

acid in acetone solutions with an apparent dissociation

constant of about lo-7, whereas perchloric acid proved to

be a relatively strong acid in a.cet.one solutions with a

. -4 d~ssociation constant of about 10 • Extremely high values

were obtained for the limi~ing equivalent conductances. In

•

view of the fact that the limiting equivalent conductances

of most electrolytes are up to 20% higher in acetone solutions

than in water, these high values are acceptable.

Although solutions of hydrogen chloride in acetone

are relatively stable at low temperatures C78o0 c), at ordinary

temperatures hydrogen chloride catalyses the selfcondensation

of acetone to mesityl oxide. An extensive

study was made of this reaction and a mechanism proposed

for the self-condensation of acetone to mesityl oxide.

The work of Everett and Rasmussen on the cell

Pt,H2/HCl/AgCl,Ag in acetone was repeated and an improved

equation was used for calculating the standard electromotive

force of this cell. Remarkable agreement was obtained

between the present results (•0.488 volt) and the

recalculated value (-0.491 volt) from the results of

Everett and Rasmussen.

Transport measurements, although in agreement with

the work of Erdey-Gru~ proved to be extremely difficult

under present conditions, due to excessively high cell

resiptnnces.

Diffusion measurements were done on solutions of

hydrogen chloride in acetone, using hydrogen chloride

labelled with chlorine-36 and employing the capillary tube

method developed by Anderson and Saddington.

The shape of the diffusion coefficient-concentration

curve showed a resemblance to the corresponding plot for

sodium chloride in aqueous solution, but the much more

pronounced minimum possibly indicates strong association

or changes in the degree of association. Extrapolation

of the plot gave a diffusion coefficient at infinite dilution

of about 5 x 10- 5 em 2 sec -1 , which is in agreement with

the value of 4.63 x l0-5cm2 sec-l calculated by the Nernst

relation.