Calculations
moles of NaOH 0.01 rnol x mol =[NaOH] = 1000mL 17.2mL
x = 1.72 X 10-~mol
moles of H+ a t equivalence, rnol H' = rnol OH= 1.72 X
rnol
moles of Ca2+,S042rnol ca2+ = rnol S042= 1X rnol H+ = 8.60 X
rnol
rnol -- x rnol - 8.60 X 0.005 L 1L = 0.0172
simply give a table of a number of acids or polyatomic anions and indicate that these names should be memorized. One text (3) even goes so far as to state that "no easily adoptable systematic way of naming these has been suggested. Consequently, the composition and names of these common ions must be memorized." Robson (4) has given a useful flow chart for naming a large number of inorganic compounds but even that requires the memorization of the names and formulas of the common polyatomic ions. Our students have found the following scheme for naming the oxyacids and their salts to be simplifying and useful in avoiding unnecessary memorization. We stress that the principles are not original. Indeed, different textbooks use the same principles in various forms. What seems to help students is the organization of the material. It gives them a place to start, an overall organizing scheme or a "roadmap" similar to the scheme for working stoichiometry problems (5-7) which so many instructors and students have found useful over the years. The key to this system (presented in the accompanying table) is the five representative -ic acids, one for each of the
M
[Ca2+]= [S042-] = [CaS04] = 0.0172
System for Naming Oxyacids and Their Salts
M
= [Ca2+][S02-] = (0.0172)~
Representative -ic Acids in Each Group of the Periodic Table:
Discussion
The average student should be able to complete two experiments in one 50-min laboratory period, provided he or she is familiar with titration techniques. Three-significantfigure reproducibility is common. The sample analysis above was taken directly from a student's laboratory report. The values reported are very close to those listed in the Handbook of Physics and Chemistry (CRC: Ksp= 0.00019). The column as described holds a maximum of about 150 pmol calcium ion. At least 30 pmol (about 2 mL) should be used for three-significant-figure accuracy. The column may be reused a t least 30 times without any significant change in performance, even though the repeated acid washes will change the color of the resin. This procedure is extremely rapid and precise, offering the student a high chance of success. It is far superior to other Kgpdetermination labs previously used in our school. Several computer aids have been developed by the author to facilitate this laboratory exercise, including a Visicalc template for data analysis and a pH titration program that assists students in performing and analyzing the titration. For further information on these programs, please contact the author.
Ill
IV
va
VI
VII
H3B03 boric acid
HzC03 carbonic acid
H3P04 phosphoric acid
H2S04 sulfuric acid
HCI03 chloric acid
Rules for Naming Other Oxyacids
...
(1) Addition of 1 oxygen to the acid: per -ic acid (2) Subtraction of 1 oxygen from the acid: . . -ous acid (3) Subtraction of 2 oxygens from the acid: hypo . . . -ous acid (4) All other analogous acids in the same group of the periodic table are named similarly.
.
Rules for Naming Anions of Oxyacids (1) (2) (3) (4)
a
Acids ending with "-ic" are associated with anions ending with "-ate". Acids ending with "-ous" are associated with anions ending with "-ite". The anion is obtained by removing all the hydrogen ions. Anions in which one or more but not all the hydrogen ions have been removed are named with the number of remaining hydrogens indicated before the name of the anion as determined using rules 1-3. If one of two hydrogen ions are removedthe anion is commonly referredto using the bi- prefix.
HNOs is an exception to the other acids in Group V and is called nitric acid.
ACID
Remove all
ANION
ÑÑÑÃ
Hydrogen ions
per- -ic
Making Sense of the Nomenclature of the Oxyacids and Their Salts Glen E. Rodgers, Harold M. State, and ~ i c h a r dL. Bivens
per-
ÑÑÑÑ
-ate
-ate
-ic ÑÑÑÑà (Starting Point)
Alegheny College Meadville, PA 16335
The nomenclature of inorganic compounds, particularly the oxyacids and their salts, is often a source of frustration for freshmen chemistry students. While some introductory textbooks (1) do present some methodology for mastering the names of these compounds, a surprising number do little or nothing to help students make sense out of what appears to them to be an "arbitrary procedure" (2). Many texts
hypo- -ous
ÑÑÑÃ
hypo- -ite
Nomenclature "roadmap". Removing less than all hydrogens results in ions covered in Rule 4 in the table.
Volume 64
Number 5
May 1987
409
