Historical Articles

A COURSE OF INSTRUCTIONS

Given by the Philadelphia Branch by Willard M. Scott, Librarian

December, 1924

The remarkable progress this branch has made in the chemical class is indeed an incentive for the other branches, and a step forward in the direction of scientific electroplating.

The large attendance throughout the elementary chemistry course, which is dry and hard to comprehend, is indicative of the fact that this attendance will continue in the future. The enthusiasm of the twenty-five students, who for the first time made an analysis of a solution, was evidence of their desire to make themselves more efficient in their science.

The instructor, Mr. Graham, who is affiliated with the University of Pennsylvania faculty, has shown the necessity of each subject and what it leads to avoiding unnecessary topics, and including volumetric analyses pertaining only to our plating solutions. I know it would be impossible to obtain at any institution such an abbreviated course in chemistry.

In our past studies we have talked about normal solutions, we defined the normality of an acid by the hydrogen factor of the solution, and you will recall that we took the molecular weight of hydrochloric acid 35.5 for chlorine 1 for hydrogen equals 36.5 and divided by the number of atoms in the hydrogen. This holds good in nearly all cases; this particular one being 36.5 grams of acid to a liter to make a normal solution, and this solution will be used in our first analyses.

Now we do know the definite strength of this standard solution, and we know that a normal solution of any acid contains 1.008 grams of ionizable hydrogen per liter, and that a normal solution of any base contains 17.008 grams of ionizable hydroxyl per liter. It is evident that a liter of one exactly neutralizes a liter of the other, or equal volumes are equivalent, so to determine the strength of an Unknown sodium hydroxide solution we use the above normal acid, and we do this by titrating one against the other.

We measure out a definite volume of Na OH, say 16 cc in a beaker, and a few drops of phenolphtalein solution are added to this which of course turns blue.

We then carefully run in drop by drop of the normal acid solution until one extra drop turned the blue to red. This showing just enough acid to react with the base, and in reading the burette we found it took 20 cc of acid to neutralize 16 cc of the unknown Na OH.

This may be expressed as follows:

Volume of acid equals Normality of base/ Volume of base equals Normality of acid = Equals Normality

We have for the first time made an analyses of a solution, finding the contents in ounces per gallon, and the above method will be applied to nearly all titrated analyses.