chemistry laboratory is included in the curriculum of a Basel type C Gymnasium, which is cited as representative of Swiss type C Gymnasia. However, in the detailed description of the curriculum (pp. 183-4), Rickover does indicate two laboratory hours (not elective and therefore, by implication, required) in agreement with Dr. Christen's statement. Confronted with this inconsistency, I unfortunately chose to utilize the summarizing table rather than the detailed text. My value judgment concerning "the virtual absence of actual laboratory experience" should be interpreted in the context of the paragraph in which it appears. The Gymnasium curriculum is being compared with the ACS "Minimum Standards Used as Criteria in Evaluating Undergraduate Professional Education in Chemistry," an admittedly stringent set of standards for a four-year college. As the initial sentence of my next paragraph states: "This comparison is not intended to downgrade the chemistry curricula of Swiss Gymnasia. . . ." The subject of textbooks, raised in the final par* graph of Dr. Christen's letter, was one of the many interesting aspects of Swiss education that I was forced to omit because of space limitations. I might take this opportunity to point out that European educators, in common with their American colleagues, are turning increasingly to the use of inexpensive paperback texts. I n Switzerland, one of the most highly respected and widely used chemistry paperbacks a t the Gymnasium level is Dr. Christen's "Allgemeine Chemie."
In all these examples a buffer solution is compared with water. The great difference in pH change is partly a consequence of the logarithmic definition of the pH scale and not due solely to the buffering action. Students soon become aware of this when they are confronted with neutralization curves. The familiar diagram shows the neutralization curves of a strong acid (dotted line) and a weak acid (solid line) by the addition of sodium hydroxide solution. It is clear that the initial part of the neutralization curve for a strong acid-strong base is considerably flatter than that for the weak acid-strong base. I n other words, the unbuffered solution is showing a greater resistance to pH change than the buffered solution of a weak acid and its salt. Once again the dilemma is due to the logarithmic definition of the pH scale. Here it works in reverse to that of the previous example. Once it is pointed out to the student that the p H is changing more slowly in the strong acid-strong base case because of the logarithmic definition of pH, he soon sees that the statements produced in many t e x t b o o k ~ t h a tonly buffer solutions (a weak acid and its salt or a weak base and its salt) are capable of resisting changes in pH and that the pH of unbuffered solutions are extremely sensitive to added acid or alkali-need modification. The test of a buffer solution is not solely whether it resists changes in pH, but whether it is able to absorb to a large extent added H+ or OH- ions. Solutions of a strong acid or a strong base will resist changes in pH, but cannot absorb added H + or OH- ions. Naturally solutions buffered at pH approaching 7 will undergo a relatively greater pH change than those buffered at higher or lower pH because of the logarithmic definition of the pH scale.
N. K. ROBERTS
T o the Editor: There are many instances of poor pedagogical practice and even errors in textbooks. Your Textbook Errors column is handling the latter very well. However, I should like to point out an instance where we are dealing perhaps with the borderline between error and poor pedagogical practice, an area which is often more subtle and consequently more misleading for the student. For example, many textbooks quote a most misleading illustration of buffer action. The argument runs this way: Consider 1 liter of pure water (its pH is 7); on the addition of 1 ml of 0.1 N HCI the pH changes to 4, a change of 3 pH units. On the t h e hand the m e volume of acid, added to 1 liter of a 1:1 mixture of sodium acetate and acetic acid, will cause almost no 5 change in the pH of 4.8. Afairer illustration would be to consider --' the change in pH of a strong acid a t pH 4.8. The addition of 1 ml of 0.1 N strong acid to 1 liter of &3; unbuffered acid of p H 4.8 would change the pH to 3.9, a change of 21*-O;,, HCI only 0.9 pH units. or -0.1 N A s e R ~ c i d
T o the Editor: I n the November issue of THIS JOURNAL [42, A903 (1965) 1, Demonstration No. 246 of the Tested Overhead Projection Series described an experiment to achieve the triple point of the system nitrobenzene-wateracetic acid, but unfortunately failed to note the toxic hazards of nitrobenzene. This compound is quite insidious because it smells much like shoe polish and imparts a certain euphoria before doing its damage. It is possible to lessen danger from nitrobenzene by avoiding overheated laboratories (hence keeping the vapor pressure minimal) and by carrying out the operations in a well-regulated hood. One should note that the maximum allowable concentration for nitrobenzene in air is 5 ppm, while hydrocyanic acid has a maximum allowable concentration in the range of l(t-20 ppm.
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Journal of Chemical Education
