To the Editor: The article "Is There an Alternative to pH?" by Francis E. Crane, Jr. [J. CHEM.EDUC.,38,365 (1961)l included an excellent literature review and an interesting proposal. Like Crane, we recognize the difficulties associated with an understanding of pH by the layman and the beginning student. For example, our experience has shown that the average swimming pool maintenance man does not readily associate the number 7 with a neutral solution. As might be anticipated, the decrease or increase in pH values representing changes in acidity and alkalinity are seldom comprehended outside of the chemical laboratory. In an attempt to prevent the recurrence of mistakes that are prevalent in swimming pool maintenance, we have devised another alternative scale as follows. [Acidity factor = (log [H+] 7)14.3.]
+
Comparative Values for Representing Acidity IH+1
VH
Acidity factor
The acidity factor is zero for a neutral solution. Acidity factors for alkaline and negative solution.: are negative and positive. Surveys conducted among groups representing swimming pool operators and corrosion engineers indicated a preference for the acidity scale over the pH scale. Like Crane, we propose to supplement hydrogel1 ion activity and pH values, not to replace them. The acidity scale was developed primarily to provide a useful tool for those who fail to comprehend either pH or hydrogen iou activity.
To the Editor: R. Chandra, who wrote the article entitled "NonCyanide Detection of Cadmium in the Presence of Copper" 138,409 (1961)], failed to indicate the chemistry involved in some of his procedures. Procedure I, about which the author invited comments, is based on the soluble complex anion [Cu(Cz0d)]-2,which is formed with copper (11) in the presence of excess oxalate [H. SCHAEFER AND R. ABEGG, Z. anorg. Chem., 45, 293 (1905)l; H. L. RILEY, J . chem. Sac., 1929,1307; H. T. S. BRITTON AND M. E. D. JARRETT, J. Chem. Soc., 1936, 1489; and L. MEITES, J . Am. Chem. Soc., 7 2 , 184 (1950), give quantitative 638
/ Journal of Chemical Education
data concerning this ion], and the equilibrium between the relatively insoluble Cd(Cn04)[K,, = 1.44 X see W. C. VOSBURGH AND J. F. BECKMAN, J . Am. Chem. Soc., 62, 1028 (1940)l and a very weak complex anion [Cd(C204)2].-2 Instability constant with respect to CdC201is about 0.034 according to Voshurgh and Beckman, op. cit. The low stability of the complex anion of cadmium causes most of the cadmium to remain precipitated even with excess oxalate. With regard to Procedure 11, copper is known to form complex anions with both carbonate and bicarbonate ions. On the basis of polarographic measurements, Meites (op. cit.) has suggested that these are [Cu(CO&V4and [CU(HCOJ~]-~, respectively. The latter may also have a molecule of water coordinated to the copper or may actually be a carbonato complex, as carbonate ions are in equilibrium with the bicarbonate ions. A largenegative charge would be built up, however, if all five are carbonate ions; therefore, the actual complex may he a mixed one. The carbonato complex is not of sufficient stability to overcome basic carbonate and hydroxido precipitation a t higher pH's.
To the Editor: The intriguing article by Schultz and Sichels regarding the pyrolytic decomposition of carhoxylate salts to ketones [THISJOURNAL, 38, 300 (1961)l raises the question as to the best laboratory method to use in preparing cyclopentanone from adipic acid. To answer this question, the following two experiments have been carried out. In the first experiment, 14.6 g of powdered adipic acid was heated in a 125-ml distilling flask fitted with a thermometer which reached into the reaction mixture. The flask was heated with an open flame, and a reaction temperature of 315-330' was required before an appreciable amount of product distilled over. One and onehalf hours was required to complete the reaction. I n the second experiment, the same amount of adipic acid was mixed with 1.6 g of Ba(OH)?.8H,O before the reaction was started. The reaction proceeded smoothly a t 280-295' and was complete in 45 minutes. Both reaction products were washed with 5 ml of water saturated with sodium bicarbonate and sodium chloride, and each was then dried over 1 g of calcium chloride. Each was distilled from a 1D-ml distilling flask. The portion boiling between 126 and 132' was retained as cyclopentanone. The yield from the first experiment was 4.3 g while that from the second was 4.5 g. While the difference in yields is not significant, the shorter reaction time and lower temperatures for the reaction in the presence of barium hydroxide suggests that the common laboratory preparation as given in many manuals is still the method of preference.
